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SAFETY VALVE
(1700 SERIES)
Pub.No 7056
Bharat Heavy Electricals Limited
Tiruchirapalli
2
CONTENTS
INTRODUCTION
SAFETY PRECAUTIONS
DESIGN FEATURES AND CONSIDERATION
HANDLING, STORAGE AND PRE -INSTALLATION
CHECK LIST FOR STORAGE, ERECTION AND COMMISSIONING
RECOMMENDED INSTALLATION PRACTICE
OUTDOOR SAFETY VALVE INSTALLATION
INDOOR SAFETY VALVE INSTALLATION
GENERAL CONSIDERATIONS
OPERATION
FIELD SETTING
POPPING POINT ADJUSTMENT
RING ADJUSTMENT REFER PAGE 9 (A)
LOWER RING ADJUSTMENT
UPPER RING ADJUSTMENT
BLOWDOWN ADJUSTMENT
SEALING VALVES AFTER TEST
DISASSEMBLY
WITH RETENTION OF SPRING SETTING
DISASSEMBLY TO COMPONENT LEVEL
MAINTENANCE
LAPPING PROCEDURE
CHECKING SPINDLE RUN-OUT
RE-ASSEMBLY
REASSEMBLY WHEN SPRING LOAD RETAINED
REASSEMBLY OF VALVE FROM COMPONENT LEVEL
LOWER ADJUSTING RING
UPPER ADJUSTING RING
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DETERMINING RING POSITION WITH VALVE UNDER PRESSURE
LIFT ADJUSTMENT
OVERLAPADJUSTMENT
HYDROSTATIC TESTING AND GAGGING
HYDROSTATIC TEST PLUG REMOVAL
FIELD SERVICE AND REPAIR
FACTORY SETTING VS. FIELD SETTING
RECOMMENDED SPARE PARTS FOR 1700 SAFETY VALVES
MAINTENANCE TOOLS AND SUPPLIES
GUIDELINES FOR THE STEAM TESTING OF BOILER SAFETY VALVES
4
INTRODUCTION
The 1700 series safety valves are manufactured in India by Bharat Heavy Electricals
Limited,Trichirappali under the licence agreement with m/s.Dresser IndustrialValveDivision,U.S.A.
These valves are intended for service in power boilers at pressures upto 213 barg(3090psig) and
temperatures upto 604.4o
C(1120o
F). Thesee valves are manufactured, tested and certified as per
Indian Boiler Regulations.
Bharat Heavy Electricals Limited
Tiruchirapalli-India
5
SAFETY PRECAUTIONS
* Do not go near discharge side of a safety valve
* Body drain and cover plate vent must be piped to a safe area.
* If left open,steam will escape and present a burn hazard to personnel near the valve.
* Always gag a safety valve before making ring adjustments.
* When pulling hand lever for inspection purposes,a rope should be attached to the handle of
sufficient length (minimum 6 to 10m long) to protect the operator from escaping steam,
dust, fly ash etc.,
* Exercise caution when examining a safety valve for audible leakage.
SUPER HEATED STEAM IS NOT VISIBLE.
* Safety valves should be mounted to provide adequate access, 3600
around the valve plus
overhead,for disassembly and maintanence.
* Use ear-muffs during the adjustment of valves.
* Use hand gloves during adjustment of valve in the hot condition.
6
DESIGN FEATURES AND CONSIDERATION
(1700 Series)
1.1 Body and Neck Materials
All pressure retaining parts, with the exception of reheat valves rated to 62.1 bar (900 psi) and
lower, are made of forged materials. Forged welded inlet neck valves have the three-piece weld
construction; flanged inlet valves and cast neck welded inlet valves have a top-inserted seal-welded
seat bushing.
1.2 Service Life
For most service conditions, pressure retaining parts and parts subject to mechanical stresses, such
as valve necks, yoke rods, etc., are designed for a service life equivalent to the boiler and well in
excess of the requirements of the Power Boiler-Code and IBR.
1.3 Thermal Compensation
The valve has been designed to provide temperature compensation. Minor adjustments may be
required in some extreme temperature variation conditions.
1.4 Thermodisc
The thermodisc design in providing for the rapid equalization of temperature around the valve seat,
provides a degree of tightness far above that offered by competitive valves. Thermodiscs are now
giving excellent results upto 379.3 bar (5500 psi) and 621°C (1150°F)
1.5 Blowdown.
The Safety Valve can be set with 3% attainable blowdown certified by the National Board of Boiler
and Pressure Vessel Inspectors.
1.6 Operating Gap
Safety Valves are tested and proven tight for operating gaps of 5%,operating gap being defined as
the difference between operating pressure and the low set pressure valve. Although tightness is a
function of design, it should be realised that with smaller operating gaps it is also necessary to
increase maintenance. Increases in incidents of valve lift, simmer, etc., can be expected because of
less allowance for system pressure transients and other unidentified variables.
2. HANDLING, STORAGE AND PRE -INSTALLATION
Safety valves should be stored in a dry environment to protect them from the weather. They should
not be removed from the skid’s or crates until immediately prior to installation. Flange protectors
end covers and sealing plugs should also be installed until just prior to installation. When Safety
Valves are uncrated and the flange protectors removed immediately prior to installation, meticulous
care should be exercised to prevent dirt and other foreign materials from entering the inlet and
outlet ports while bolting or welding in place. Ensure the disc is available. Identify the disc and
store it safely with D.U sequence required for assembly. Check for disc identification dimension
before assembly table 4.
The valve, either crated or uncrated, should always be kept with the inlet down i.e., never laid on its
side, to prevent misalignment and damage to internals. Keep valve on cradle after removing from
crate. Uncrated valves should be moved or hoisted by wrapping a chain or sling around discharge
neck, then around upper yoke structure in such a manner that will insure the valve in vertical position
during lifting i.e., not lifted in horizontal position. Never lift the full weight of the valve by the
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lifting lever. Never hook to the spring to lift. Figure shows the correct way of lifting the valves.
Crated valves should always be lifted with the inlet downwards.
Safety valves, either crated or uncrated, should never be subjected to sharp impact. This would be
most likely to occur by pumping or dropping during loading or unloading from a truck or while
moving with a power conveyor, such as a fork lift truck. While hoisting to the installation, care
should be exercised to prevent bumping the valve against steel structures and other objects.
2.1 Check list for Storage, Erection and Commissioning
i. Check for tag No.or D.U.No. as per packing slip. Non-availability or discrepancy must be
informed to the manufacturing unit. Check for test certificates for each safety valve.
ii. check whether the inlet size, orifice, material grade, set pressure etc.are as per the boiler
O&M Manual.
iii. check that the seals are intact on ring pin, spring adjuster and overlapcollar. Check for
transit damages, if any.
iv. Ensure that the end covers are kept in position and removed only just before erecting in
place. Meticulous care should be taken to ensure dirt or foreign particles do not enter into
the inlet or outlet of the valve.
v. Ensure the valves are stored in crates on sleepers in a covered area with the inlet side
downwards. Valves should never be laid on the side to avoid damage to internals.
Erection
vi. Ensure that the disc is available, identify and keep in a safe place for final assembly as per
D.U. sequence. Identify and hand over the Hyd.test plugs to the user after the Hyd.test is
completed.
a. Ensure proper preservation for exposed surfaces of valve and service tools for long storage.
b. Ensure the valves are never subjected to impact by bumping or dropping during loading
and unloading and disassembly and assembly of valve.
c. Do not lift valve with lever or spring. Sling valve as per O&M.
vii. Valves should be erected with spindle vertical within a tolerance of ± 1° from the vertical
plane.
viii. Ensure proper pre-heating and post heating,stress relieving and NDT procedures are
followed when welding to the stub.
ix. Ensure that the vent pipe is separately supported and does not touch the drip pan unit and
that there is sufficient allowance for expansion in horizontal and vertical directions.
x. Ensure the cover plate vent and drain are connected with pipe of adequate size to safe
locations.
xi. Extend insulation of vent pipe over roof to avoid rain water collection into drip pan. Insulate
the inlet and body upto the cover plate.
xii. After hydrostatic test of boiler, remove hydro test plug and ensure dice is replaced and
valve reassembled without affecting setting as per O&M.
Commissioning
xiii. Use calibrated pressure gauges for safety valve floating. Float the lowest set safety valve
first, gag the valve after setting is over and float the next higher set valve and so on till all
valves are floated and checked for the set pressure within ± 1% tolerance level.
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xiv. Try to achieve the setting within a minimum no. of pops (about 3 pops).
xv. Check that blowdown is within 5%.
xvi. Apply gag load finger tight in hot condition to avoid spindle bending.
xvii. Remove gags after floating of safety valves.
xviii. Check and ensure sufficient approach and maintenance space all around the valve.
xix. Proper structures for mounting the slings or pulley blocks are necessary for maintenance
purposes. Same may be checked during installation itself.
xx. After the valves are set in the field, release collar should be taken up and locked with
cotter pin such that min.gap of 3.2 mm (1/8”) is retained between the collar and top lever.
3. RECOMMENDED INSTALLATION PRACTICE
i. The safety valve or valves shall be connected be valve or valves shall be connnected to the
boiler independent 0f any other connection, and attached as close as possible to the boiler,
without any unnecessary intervening valve or fitting. Such intervening pipe or fitting shall
not be longer than the face-to-face dimension of the corresponding tee fitting of same
diameter and pressure. Every safety valve shall be connected so as to stand in an upright
position with spindle vertical.
ii. The opening or connection between the boiler and the safety valve shall have atleast the
area of the valve inlet. No valve of any description shall be placed between the required
safety valve and the boiler nor on the discharge pipe between the safety valve and the
atmosphere. When a discharge pipe is used, the cross-sectional area shall not be less than
the full area of the valve outlet of the total of the areas of the valve outlets discharging
there into.It shall be as short and straight as posssible and so arranged as to avoid undue
stresses on the valve or valves.
All safety valve discharges shall be so located or piped as to be carried clear from running
boards or platforms. Ample provision for gravity drain shall be made in the discharge pipe
or near each safety valve or safety relief valve, and where water or condensation may
collect. Each valve shall have an open gravity drain through the casing below the level of
the valve seat. For iron and steel-bodied valves exceeding 63.5 mm (2-1/2") size, the drain
hole shall be tapped not less than 9.5 mm (3/8") pipe size.
iii. If a muffler is used on a safety valve or safety relief valve, it shall have sufficient outlet
area to prevent back pressure from interfering with the proper operation and discharge
capacity of the valve. The muffler plates or other devices shall be so constructed as to
avoid a possibility of restriction of the steam passages due to deposits.
When a safety valve is exposed to outdoor elements which may affect operation of the
valve, it is permissible to shield the valve with a satisfactory cover. The shield or cover, shall
be properly vented and arranged to permit servicing and normal operation of the valve.
iv. Safety valves may be attached to drums or headers by welding provided the welding is
done in accordance with Code requirements.
3.1 Outdoor Safety Valve Installation
Safety Valves operating under the best possible conditions of favourable operating gap, relatively
stable ambient temperatures, absence of dirt and in relatively still air, will provide the maximum
degree of safety, tightness and dependability.
When a safetyvalve is installed in a location such as out of doors, it is exposed to wind, rain, snow,
ice, dirt and varying temperatures.
9
The following recommendations are made for proper protection to insure that operational
dependability can be restored to a level near that of the valve installed under ideal conditions.
The inlet neck of the safety valve and safety valve body, upto the bottom of the cover plate. should
be insulated. The exterior surface of any such insulation should be weather proofed by any suitable
means. In addition to maintaining a more even temperature with in the valve body, during widely
fluctuating ambient temperatures, this insulation will effectively reduce thermal stresses due to
high temperature gradients through the walls of the safety valve nozzles. Even in tropical latitudes,
insulation should be applied since safety valves installed in outdoor locations in these areas are
subject to hurricane conditions.
Spring covers should be used to stabilize as nearly as possible the temperature of the spring and
also to prevent the accumulation of dirt, ash, and ice between coils of the spring..
Lifting gear covers should be installed to prevent ice, dirt and fly ash from accumulating in areas
inside the safety valve cap.
3.2 Indoor Safety Valve Installation
In-door-valve installations should have inlet necks insulated only upto the underside of the valve
body Considerations should be given to ambient temperatures of greater than 38.8°C (100°F;)
because of possible set point change which may occur due to higher ambient temperatures.
3.3 General Considerations
i . Excessive pressure loss at the inlet of the safety valve will cause extremely rapid opening
and closing of the valve, which is known as “chattering” .Chattering may result in lowered
capacity as well as damage to the seating surface of the valve. Severe Chattering can also
cause damage to other parts of the valve.
The following recommendations will assist in eliminating the factors that produce chatter.
a. The area of the inlet nozzel should he atleast equivalent to the inlet area of the safety
valve and that nozzle should be short as possible.
b. Inlet nozzle corners must be rounded to a radius of not less than 1/4 of the diameter
opening.
c. Pressure drop to the inlet of the valve should not be greater than 50% of the expected
blow down of the safety valve.
d. To eliminate the effects of a phenomena known as sonic vibrations, the following
recommendations are made.
Safety valves should be installed atleast eight to ten pipe diameters down stream from any
bend in a streamline. This distance should be increased if the direction of the change of the
steam flow is from vertical upwards to horizontal in such a manner as to increase density
of the flow in the area directly beneath the safety valve nozzles.
Safety valves Should not be installed closerthan eight to ten pipe diameters either upstream
or downstream from diverging or converging “Y” fittings In cases where piping
configuration renders thc two above recommendation impractical or impossible, the
downstream corners of the nozzle inlets should be rounded, leaving the upstream corners
square. The nozzle entrance should be rounded so that the radius at the downstream corner
will be equal to one-fourth of the nozzle diameter. The radius should be reduced gradually
leaving only a small portion of the upstream corner sharp.
The safety valve nozzle should never be installed in a steam line in a position directly
opposite a branch line of equvalent size.
10
ii. Excessive steam line vibrations are known to produce shifts in safety valve set pressures.
Results of sizable vibrations will be to introduce possible chatter with ultimate damage to
the valve in addition to reduced capacity Such line vibration should be examined for
optimum valve performance.
iii Exhaust, drain and cover plate vent piping must be installed so that they will not impose
under stresses on the safety valve .These stresses can produce distortion and Ieakage at
pressures below the set point.The following recommendations should be noted:
a. Discharge piping should not be supported by the valve. The maximum weight on
the outlet of the valve should not exceed the weight of a discharge flange, elbow
and drip pan unit.
b. Clearances between the valve exhaust piping and the discharge stack should be
sufficient to prevent contact when considering thermal expansion of the boiler ,
valve , discharge stack and increased stack movement due to vibration and
temperature when the valve is relieving.
c. Flexible metal hoses if used to connect safety valve outlets to discharge slacks, must
have sufficient length and must be designed and installed in such a manner that they
will not become “solid” in any position of the valve. Better results are obtained if the
hoses are installed so that they will permit movement by bending, rather than by stretching
and compressing along their length.
iv. Steam flowing vertically out of the discharge elbow produces a downward reaction on the
elbow, in proportion on the quantity of steam flowing and its velocity. In large, high capacity
valves this force can equal several thousand kilograms and can produce severe stresses in
the valve necks. The bending stresses are determined by the amount of the reactive forces,
combined with the moment arm, or horizontal distance between the vertical centreline of
the valve and the vertical center line of the outlet elbow.
v. In no case should discharge piping be of a smaller size than the valve outlet .The length of
the discharge stack will govern its size and with increased lengths, stack diameters will
increase. This will prevent blow back from the discharge stack. Excessive water being
pulled through the valve will also produce a blow back under certain conditions and should
be investigated prior to faulting the discharge stack.
vi. For optimum performance, safety valves must be serviced regularly and maintained. So
that servicing can be properly handled safety valve should be located for easy access.
Sufficient working space should be provided around the safety valve to permit access to
adjusting rings. If two or more safety valves are located close together, the outlets should
be parallel, to offer as much protection as possible to personnel repairing or working close
to the safety valve. Cross beams may be provide above valve centre line for easy disassembly
of safety valves.
vii. For valves being installed that are tested for set pressure with the use of a hydroset, it
should be realised that only the set pressure is being verified. Other factors such asblow
down, lift, reaction force, proper inlet welding, proper discharge stack sizes and effects
of thermal expansion cannot be determined.
viii. Because foreign material passing into and through a safety valve may damage it, the system
on which the valve is tested and finally installed must also be inspected and cleaned. New
systems, especially, are prone to contain welding beads, pipe scale, and other foreign material
which are inadvertently trapped during construction and destroy the sealing surfaces the
first few times the valve opens. Wherever possible, the system should be purged thoroughly
before the safety valve is installed.
11
It is recommended that the safety valve be isolated during hydrostatic testing of the boiler
either by blanking off the valve, gagging the valve, or installation of hydrostatic test plugs.
ix. For weld-end inlet valves, completely assembled valves may be installed with out necessity
for disassembly. Vertical alignment should be within ± 1° from a vertical plane. During
welding, where possible, the valve neck should be insulated to reduce thermal effects.
When stress relieving, the same will apply. In all cases the valve neck should be insulated
atleast upto the inlet neck-valve body bowl juncture.
x. It is of outmost importance that the gasketing used be dimensionally correct for the specific
flange and that if fully clears the valve inlet and outlet openings. Gasket, flange facings,
and bolting should meet the service requirements for the pressure and temperature involved.
When installing flanged inlet valve, the flange bolts must be pulled down evenly in order
to prevent body distortion and consequent misalignment and leakage.
xi. On new installations, during initial setting of safety valves there is a possibility of damaging
the superheater valve seat due to foreign matter, such as mill scale, weld spatter and beads,
etc., being drawn into the steam flow.
This foreign matter batters and cuts the seats of the valve although damage to the bushing
seat is usually considerably less than to the disc seat. This type of damage causes the valve
to leak quite badly and generally requires that the disc be replaced and the bushing seat
relapped.
Before bringing the boiler down, the leaking valve should be hand-blown atleast ten times
and held open for a period of one minute each time. This should clean any remaining
foreign material out of the superheater and minimise the possibility of damage to the seats
after overhaul, although this particular trouble sometime persists until the boiler has been
operating for a considerable period of time.
Drum safety valves do not, generally, draw foreign matter into the steam flow, and no
difficulty of this type to be expected
3.4 Cover Plate Vent Piping
The vent piping of the cover plate can be installed in one of the three ways.
First, the cover plate can be piped upto the drip pan as shown in Figure 1. Second, the cover can be
vented to atmosphere as in Figure 2. Third, the vent can be directed toward the discharge stack as
shown in Fig.2a. Precautions should be taken to vent cover plate in such a manner that it will
exhaust into a safe area to prevent injury to personnel near the valve.
CAUTION: Do not plug cover plate vent hole or reduce vent hole pipe size.
Precautions should be taken to prevent accumulations Foreign material or water in the vent
pipe. This vent is a critical part Or the valve system for controlling valve blowdown and lift.
4. OPERATION
The safety valves operate during closing with a back pressure principle, that is, the force of trapped
steam on the upper side of the disc holder is utilized to assist the spring in forcing the disc back
down on its seat.
Reference to Fig.3 for illustration and Fig.20 for nomenclature, it will be seen that when the valve
is blowing, a small amount of steam is bled from the huddle chamber (A) through holes (B) into
chamber (C) and escapes to the atmosphere between floating washer (D) and overlap shoulder (E).
The steam also flows through an internal orifice and out through (F).
As the inlet steam pressure drops,the overlap shoulder (E) upon reaching the top of the floating
12
washer (D) traps steam in chamber (C), builds up pressure on top of the disc holder, and assists the
spring in closing the valve.
The distance from the top of the floating washer (D) to overlap shoulder (E) is therefore. ,an important
function in the operation of the valve and must be correct in dimension.
Table 2 gives the correct initial overlap dimension corresponding to bore size.
4.1 Field Setting
All Safety valves are steam tested at the factory. Every valve is set to have a clean popping action
and to reseat tightly. However, because the boiler used In setting the valves has a small capacity
compared to the capacities of the valve. Slight adjustments on the actual installation are necessary
to maintain proper action and blowdown.
Two methods exist for field testing of valves ;use of the 1566 or 1566-2, Hydroset Unit,and full
system pressure.
As previously noted, the use of a hydroset unit will serve to establish Set pressure only and should
not be used for establish blowdown, lift, etc., Gagging of other valve not being set generally will
not be necessary; however, for setting of high set pressure valves, depending on system pressure
being used, it may be required to gag the lower set valves.
Boiler safety valves tests can be conducted with the unit either on or off the line.However, with the
unit on the line at full load a sudden load drop could be dangerous as most of the safety valves will
be gagged. Therefore, it is recommended that the safety will be tested and adjusted with unit off the
line or with light load. Boiler control can then be maintained with little or no outside influence due
to load change.
The valves should be set within ±1% of the set pressure. Set pressure should not be changed without
the permission of the manufacturing unit.Lab standard or test Gauges should be used with a minimum
graduation of 0.5% of the full scale reading and accuracy of ± 0.25%.Gauges should be of sufficient
range so that reading is in the middle third of the scale.
Factors Which Can affect Safety valve operation are:
i. Ambient temperature
ii. Discharge Stack Binding against drip pan elbow.
iii. Vibration of the header from upstream bends, etc.,
4.2 Popping Point Adjustment
To change the popping pressure of the valve remove the cap and lever assembly, loosen the locknut
and turn the spring adjuster clockwise to increase pressure. After each adjustment of the spring
adjuster the locknut should be tightened. The arm on top of spring washer should always be free
from bearing against the yoke rod. This can be accomplished by holdingAscrewdriver between the
arm and the rod to prevent any movement of the top spring washer while adjusting the spring
adjuster.
4.3 Ring Adjustment Refer page 9 (a)
Always gag the Safety Valve for protection, in case boiler pressure rises while making ring
adjustments (See instructions for gagging).
The positions of the upper adjusting ring and the lower adjusting ring are locked by means of the
upper adjusting ring pin and the lower ring pin respectively. These pins are threaded into the valve
body and engage notches which are cut into the rings. To adjust either ring the corresponding ring
pin must be removed. A screw driver can be used to turn the rings.
13
Spare ring pins when supplied will be of excess length and have to be individually ground to match
each valve. The tip of the pin should not touch the bottom of the ring notches.
Lower Ring Adjustment
Using Figure 17 and Table 3, a reference plane is established where the adjusting ring is level with
the bushing seat. From this setting, factory adjustments are made by adjusting one notch downward
for each 42.2 kg/sq..cm (600psi) of set pressure. Ring position should be checked prior to testing.
Slight deviations from these settings are possible because of tests conducted in the plant.
NOTE (THIS PROVIDES A STARTING POINT ONLY). The lower ring is used to obtain a
clean popping action and to cushion the closing action of the valve.
DO NOT ATTEMPT TO ADJUST BLOWDOWN WITH THE LOWER RING.
The ideal position must then be found for the set of operating conditions present. If simmer is
present or valve fails to lift, the lower ring should be moved upward slowly, one notch at a time to
remove the simmer. The most ideal position for the lower ring is the lowest position that does not
introduce simmer or a buzzing sound.
In this connection, it is imperative that extreme care be used in conditioning the seat surfaces,
14
15
ensuring correct alignment, and establishing the proper clearance, so that mechanical causes of
simmer will be reduced to a minimum.
Upper Ring Adjustment
When shipped from the factory, upper adjusting rings are set level with the bushing seat in accordance
with Figure 17 and Table 3. This should be checked prior to field setting and should be regarded as
a starting position only. It is possible that this position is not strictly in accordance with Figure 17
and Table 3 on some valves because of testing at the plant. The ring may be set lower than the seat
level, but never before, until field tests are conducted.
Starting position for blowdown check should place bottom surface of upper ring level with bushing
seat. Since the bushing seat is not visible through the service ports. It is necessary to use a
cross-reference relationship. Raise the upper ring until its bottom surface in level with the disc
holder, which is visible through the ports. Then, referring to Table 3, Column B, lower the upper
ring the required number of notches. This will place the upper ring on a plane with the bushing seat.
This is the starting point for blowdown tests. Further adjustments may be necessary depending on
test results.
When further adjustments are required to obtain final blowdown setting, the upper adjusting ring
should be moved 5-10 notches at a time as follows:
Guidelines for setting and locking adjusting rings
Gag the safety valve for protection while making ring adjustments.
The lower and upper adjusting ring pins of any particular valve is not interchangeable.
Spare ring pins when supplied will be of excess length. These pins are to be ground at site so as to
match the valve under maintenance.
The tip of pin should NOT touch the bottom of the ring notch (refer sketch enclosed) Also the pins
should not bear against the rings.
DO NOT attempt to adjust blow down with the lower ring.
The upper adjusting ring should not be set below the seat level and the lower adjusting ring should
not be set above the seat level.
Lock both the ring pin settings using a seal wire to avoid disturbance during system/valve operation
and line vibrations.
FIG 3: ` SECTION ILLUSTRATING OVERLAPAND BACK PRESSURE SYSTEM
16
Ensure that the above settings are properly locked: Periodically check whether the pins are in their
appropriate place and are effective. This can be checked through the service port ,provided in the
valve body.
A sketch showing acceptable ring pin positions is enclosed.
Excessive line vibrations, presence of foreign particles, discharge piping stress, back pressure, reaction
force etc., can lead to pin failure over a prolonged period of exposure. The ring pins being the most
critical spare part, it is desirable that one pin per valve (for drum and SH SVs) and one ring per four
valves (for RH SVs) is stocked as essential spares by customer.
Adherence to the above aspects would eliminate cases of premature pin failure and lead to a
satisfactory valve performance.
To reduce blowdown -MOVE RING UP-TURN COUNTER CLOCKWISE.
To increase blowdown -MOVE RING DOWN-TURN CLOCKWISE.
It is possible to raise the upper ring too far and prohibit attainment of full lift. When this occurs,
lower to the point where full lift is attainable and finalize the blowdown setting with the overlap
collar (See Overlap Collar Position).
If valve fails to lift the lower adjusting ring requires further adjustment. (See LowerAdjusting Ring
Position)
Check the ring pins to see that the engage the ring grooves, but without touching the bottom The
pins should not bear against the rings.
17
4.4 Blowdown Adjustment
In arriving at proper blowdown adjustment of the Safety valve it is almost imperative that a lift
indicator be used (Fig4). The correct method of obtaining proper blowdown adjustment can be best
explained by reference to Fig.5
The upper ring is used to obtain full lift at the popping pressure. However, its position also determines
the point at which the valve begins to drop out of full lift and starts the closing portion of its cycle.
For example, if the upper ring is in such a position that the valve barely attains full lift at the
popping pressure and starts to drop out of full lift at a slight reduction of-boiler pressure, the first
portion of the valve cycle will be represented by the line ABF. If it were not for the lift stop, the
action of the valve would be represented by the line ABCF.If the upper ring is in a more positive
position (lower setting)the action of the valve would be represented by the line ABG and if it were
not for the lift stop, the line ABDG.If the upper ring is in a still lower position, the action of the
valve is represented by the line ABH and if it were not for the lift stop ABEH. From this it can be
seen that a lower position of the upper ring causes that valve to remain in full lift for a long period
time and over a greater period of pressure reduction.Refer Figs,6,7 and 8.
FIG 4: LIFT INDICATOR ILLUSTRATION
Fig 5: lift Diagram as explained in blowdown adjustment.
18
It will further be noted that there is a distinct
difference between the actual overlap setting on the
valve and the point at which the overlap begins to
take effect.This can be understood since the area in
the overlap vent begins to reduce considerably
ahead of the point where upper corner of the overlap
level actually enters the floating washer,Fig 7. This
has the effect of rounding off the corner of the
diagram at points J,K and L . If the Upper ring is in
a position to produce the lineABH the overlap will
have to be set considerably higher to obtain a short
blowdown than if the upper ring is set at such a
position as to produce the line ABF. Excessively
high overlap settings are liable to cause seat damage
when the valve closes. It is therefore desirable to
set the upper ring in such a position as to cause the
valve to stay in full lift for as short time as possible
most desirous complete cycle is represented by the
line ABFJM.
CAUTION: When steam safety valves are subjected
to an excessively high water level, the valve can be
expected to have a long blowdown which the upper
ring adjusting ring position will be unable to correct.It
is recommended that the cause of high water level be
corrected so valves may fuction correctly at the
intended conditions.
If a superheater valve is set with low temprature
steam, it is advisable to for increase the blowdown
to compensate the change in the density and other
thermal effects taking place when the steam is
brought up to working temperature.An approximate
rule is to add 0.5 percent of set pressure to the
blowdown for each 1000
F(55.60
C)of steam
temperature below the final temperature.
4.5 Sealing Valves after Test
After testing the valve for proper set point and
blowdown , the ring pins,and top lever pin will be
sealed for all external adjustments.Seals shall be
installed by the manufacturer at the time of inital
shipment and after field adjustment or repair of the
valves either by the manufacturer,his authorized
representative repairer,or the user.Seals shall be
installed in such a manner as to prevent changing the
adjustment without breaking the seal and,in
addition,shall serve as means of identifying the
manufacturer ,assembler,repairer,or user making the
adjustment.Unauthorized breakage of the seals should
be reported to the concerned authorities.
FIG 6: VALVE IN FULL LIFT-
OVERLAP IN FULL OPEN
POSITION
FIG7: VALVEININTERMEDIATELIFT-
OVERLAP SLIGHTLY ABOVE
FLOATING WASHER
19
5. DISASSEMBLY
Safety Valve can be easily disassembled for inspection,reconditioning seats,or replacing ternal
parts, without altering the spring load and hence the set pressure.Refer to Fig.20 for nomenclature
Before starting to disassemble the valve,be sure that the there is no steam pressure in the drum or
header then proceed as follows:
5.1 With Retention of spring setting
To retain the spring setting of the valve when and only when,a disc is to be replaced or the seating
surfaces are to be touched up the following procedures should be followed. Remove the top lever
pin and top lever. Loosen cap set screw and lift off cap and drop lever assembly.Remove the cotter
pin and turn the Release collar down until it is tight against the top of the spring adjuster,then back
off ¼ turn. Install cotter pin in lower hole of spindle. Remove the two top yoke rod nuts and the four
cover plate studnuts,and lift the spindle,spring and springwashers,cover plate,disc and disc holder
assembly out of the valve .see Fig 9.
FIG 9: PARTS REMOVED
WHEN RETAINING SETTING
5.2 Disassembly to Component Level
Remove theTop Lever Pin and Top Lever. Loosen Cap, set screw and lift off Cap and drop lever
assembly. Remove Cotter Pin and release Collar. Remove the two Top Yoke Nuts, the Yoke and
Spring adjuster with locknut as an assembly. Then lift the spring and spring washers from the
spindle.
Unscrew the four cover plate Stud Nuts then lift the Spindle, Cover plate, Disc and Disc Holder out
of the valve.
Remove the disc by unscrewing it from the coarse right hand thread on the spindle and remove the
disc holder.
The Guide and adjusting RingAssembly can now be removed from the Base by lifting it straight up.
In order that the blowdown of the valve will be unchanged, the position of the Upper Adjusting
Ring should be marked for reassembly. Make punch marks in an axial line on a tooth of the Upper
Adjusting ring and the outside barrel of the Guide. Then measure over all height of the guide and
Upper adjusting ring assembly and record this information.
FIG8: VALVE IN CLOSED POSITION OVER-
LAPFULLYENGAGED IN FLOATING
20
Measure and record,the height from the valvebushing seat to the recess in the base where the guide
would normally rest. This is important so that the amount of metal removed from the seat can be
determined.
Mark the lower Ring in line with the Lower Ring Pin. Now place a straight edge or a Ring Lap
across the top of the seat and count the number of notches that the ring is below the seat. Record this
information for reassembly.
6. MAINTENANCE
6.1 General
lt. is not necessary to remove flanged or welded valves from the boiler for any maintenance The
actual maintenance required is generally confined to touching of seats and occassionally replacing
the disc
The following are recommended for this
i. Flat lapping plate.
ii. Grinding compounds
iii. High temperature lubricant. Molykote G.
iv. Three ring-laps per valve.
*Refer Maintenance tools and supplies section also.
It may not be necessary to use all of the ring-laps at any one time, but having a sufficient supply on
hand will save the time of reconditioning them during a boiler outage. After the boiler is back on
the line, the ring-laps should be reconditioned on the net lapping plate or on a special lapping
machine. A lap should not be used on more than one valve without being reconditioned.
Valves that have been leaking should be disassembled in accordance with prior instructions. Since
the position of the adjusting rings has been recorded, the rings can be disassembled for cleaning if
necessary. Parts for each valve should be kept together or marked, to make sure that they are replaced
in the same valve.
Reconditioning of the seat surfaces of the disc and seat bushing is accomplished by lapping with a
flat cast iron-ring-lap coated with Grade No.1000 silicon-carbide compound, or equivalent.
6.2 Lapping Procedure
The following precautions and hints will enable anyone to do a professional Job of Lapping. seats
i. Keep work clean.
ii A lap should not used on more than one valve without being reconditioned.
iii Apply a very thin layer of compound to the lap.This will prevent rounding off the edges of
the seat.
FIG.10: RINGOR SEAT LAP
21
iv. Lap, using a figure eight motion in all directions,at the same time applying uniform pressure
and rotating the Lap slowly. Care should be used not to run off the seating surface with the
lap as this will cause the seat to become uneven. When lapping the disc seat, the Lap
should be held stationary and the disc moved as above with care taken not to strike the
cone of the disc as this would cause the seat to be high on the inside.
vi. To check the seat, remove all compound from the seat and lap.
vi. To check the seat,remove all compound from seat and lap.Then using a dry lap and the
same lapping motion as above, the low section of the seating surface will show up as
shadow in contrast to the shiny portion. If shadows are present, further lapping is necessary.
Only laps known to be net should be used, as only a few minutes will be required to
remove the shadows.
vii. When the lapping is completed, any lines appearing as cross scratches can be removed by
rotating the Lap which has been wiped clean from compound on the seat about its own
axis.
viii. To check ring laps for flatness,wipe all compound off the lapping plate and ring lap. Then
use a figure of 8 motion of the ring lap on the lap ping plate. If the lap is flat there will be n o
shadow; if there is a shadow coat the lapping plate with compound and lap the ring lap with a
figure of 8 motion covering thc lapping plate to remove the shadowFigure 11.
ix. The seat now shall be throughly cleaned, using a lint free cloth or tissue paper.
If extensive lapping of the bushing seat is required, a great deal of time will be saved if a Roto-Lap is used. See
instructions for assembling and operating the rotoLap Machine.
Referring to Fig.12 it will be noted that the seat step is 0.635mm (0.025 in.) If this step is reduced to 0.4
mm(0.010in)duetolapping,itshouldberemachinedtotheproperdimensions.Forthispurposethereis
availableforusea“ReseatingMachine”whicheliminatestheneedtoremovethevalvefromtheunit.This
machine is mounted in place of the coverplate and cuts the top face,inside diameter and outside diametre
ofthebushingtoestablishthecorrectheightrelationshipsandangles.
FIG12: BUSHING SEAT STEP
DIMENSION
FIG11: RECONDITIONING OF LAP
22
In re-machining the bushing seat, the length of the disc holder extending above the disc guide will
decrease.
Referring to the Figure 13 the top of the disc guide should be kept to a distance of atleast 1.587
mm(1/16mm) below the top of the disc holder in case a deposit of dirt forms in the pocket between
the two parts. This dimension is obtained by machining the top of the disc guide.
6.3 Checking Spindle Run-out
It is important that the spindle be kept very spindle in order to transmit the spring force to the disc
without latteral binding. Overgaging and cold gagging is one of common causes of bent spindles.A
method to check the essential working surfaces of the spindle disc is illustrated in Figure 14.
Clamp a V block (A) made of wood, fibre or other suitable material onto the platform railing .Imbed
the ball end of the spindle in a piece of soft wood (B) and place top, of spindle below the threads, in
V block (A). Clamp a dial indicator on to the railing and locate at point (C). The total indicator
reading should not exceed 0.177 mm (0.007 in.) when the spindle is rotated.
Other parts of the spindle not used as working surfaces may run out cosiderably more than0.177mm
(0.007 in.) but this should not be regarded as an indication of crookedness or faulty manufacture.
To replace the disc, disassemble the valve in accordance with the prior instructions. Then proceed
as follows:
NOTE: The bushing seat can be reconditioned by hand lapping as explained under ‘Lapping
Procedure’.
FIG 14: CHECKING SPINDLE
CONCENTRICITY.
FIG 13: HEIGHT OF HOLDER ABOVE GUIDE
23
The replacement disc has been lapped on a special lapping machine and requires only that the seat
be touched up. However, the spindle tip bearing should be re-established by grinding the spindle tip
into Ihe disc. This can be done with the removable assembly propped upon the spring adjuster end.
Then remove the old disc by unscrewing the coarse right hand thread on the spindle. Remove the
disc holder, apply a layer of grinding compound to the ball end of the spindle and screw the new
disc on. Grind the bearing using a rotary motion.
The spindle nose should be lapped into the disc spindle pocket unil the bearing band is clearly
marked. The band position is shown in Figure 15.
If the band extends too high on the radius disc may lock up under pressure. If the band is too
narrow,the spindle may indent the disc and again the rock will be lost.
The table 4 also shows the finished machined size of thespindle nose radius for each orifice size
and the flat diametre.If the required bearing band can not be obtained by hand grinding then this
radius should be checked and remachined if necessary.
When the bearing is re-established,clean both surfaces with kerosene or light oil. Then apply some
Molykote to the spherical surface of the spindle tip and work it into the pores by rotating the disc on
the spindle.
First place this holder on the spindle,allowing it to rest on the face of the disc collar. Then assemble
the disc holder and new disc. The disc should be free enough to rock on the spindle tip.If there is no
freedom ,lower the collar until the disc is free to rock slightly. Disc collar should then be lowered
two notches and secured with stainless steel cotter pin.Disc and disc holder should then be assembled.
Clearance between disc and discholder should be 0.381mm (0.015 in) to 0.508mm (0.020 in) see
Fig 16.
FIG 15 FIG.16: DISCAND DISC HOLDER CLEARANCE
24
7. RE-ASSEMBLY
7.1 Reassembly when spring load Retained
After restoring both the bushing seat and the disc seat by using the Lapping procedure. as given in
this manual the valve shall be assembled as follows: See Fig. 9 & 20.
Apply Molykote G lubricant on all threads. Hold disc holder against disc collar and thread disc onto
spindlethreads.
Turn disc clockwise until drop out threads in disc pass and disengage from spindle threads.
Clean seats thoroughly and lower complete upper assembly into valve body.
Install and tighten yoke rod nuts and cover plate nuts till the release collar is free.
Backoffreleasecollarandpositionitsothat3.175mm(1/8in.)ofclearenceisvisiblebetweenliftingfork
andreleasecollarwhenliftinggearisinstalled.
Afterpositioningreleasecollarremoveliftinggearandinstallcotterpin.Installliftinggear.
7.2 Reassembly of valve from component level
Settheadjustingringsinthepositionsnotedduringdisassembly.Ifsufficientmetalhasbeenremovedfrom
bushing remeasure distance from bushing seat to guide recess in base. Compare this with that measured
prior to machining and determine difference. The upper adjusting ring should then be lowered to this
additionalamountfromitsoriginalpositioninthevalve.
Whenstartingreassemblyifthevalvewhenoriginalringpositionsarenotknownthefollowinginformation
is to be used as a guideline.
The starting position of the rings can be determined by the following method.
i. Lower adjusting ring
Place a straight edge on the seat bring the ring up to the straight edge then backing off one notch for
each 41.4Bar (600 lbs) of set pressure, Example a valve at 165.6 Bar of set pressure shall be 4
notches below the seat. This applies upto 206.9 Bar(3000 psi) 5 notches downward is considered a
maximum lower position.
ii. Upper adjusting ring
Measure from the top of the guide to the seat,then set the the ring using the measurement as the
overall length from the top of the guide to the bottom of the ring.This will place the ring exactly at
seat level when guide and ring assembly is placed into valve body.
TABLE 4 DISC,SPINDLE CHECK DIMENSION
Orifice Nose Radius “R”
mm
Flat Dia
mm
Dia ‘d’ mm
(inch)
1 7.036+.000-.102 3.175 39.8 (1.567)
2 9.423+.000-.102 4.763 47.8 (1.881)
3 12.573+.000-.127 6.350 63.7 (2.507)
4 12.573+.000-.127 6.350 73.0 (2.874)
5 12.573+.000-.127 6.350 79.6 (3.134)
6 12.573+.000-.127 6.350 106.1 (4.179)
7 17.323+.000-.127 6.350 132.7 (5.224)
Q 17.323+.000-.127 6.350 132.7 (5.224)
8 18.110+.000-.127 7.938 150.4 (5.920)
R 18.110+.000-.127 7.938 150.8 (6.290)
25
iii. Determining ring position with valve under pressure
when valve is under pressure and the position of the rings is not known, their location can be
determined by the following method.
a. Lower adjusting ring
Raise lower ring until contact is established with disc holder.Refer to fig 17 and table 3. Column
“A” for number of notches from disc holder to seat . Example : In the case of a 1739 valve (#3
orifice) raise lower ring until it touches disc holder. Referring to Fig 17 and table 3 it will be noted
that for a # 3 orifice valve the lower ring must be moved clockwise 12 notches to place ring on a
plane with seat. Lower ring can now be positioned by lowering it 1notch for every 41.4 bar (600 psi)
of set pressure upto 5 notches maximum.
26
TABLE 3
ADJUSTING RINGS
FINAL FACTORY POSITIONS
(FIELD STARTING POSITIONS)
b. Upper adjusting ring
Remove both service port plugs (located on the left side of a valve facing outlet) and with a flash
light directed into one service port hole, the upper ring can be raised until the lower face of the ring
is on a plane with the disc holder .Referring to Table 3 Column “B” a #3 orifice upper ring will be 16
notches above the seat. Ring should be brought to seat level as a starting point of adjustment When
testing the valve refer to “Blowdown Adjustment” for effect of upper ring position.
iv. Lift adjustment
ln the event that extensive machining has been done on the bushing seat of the valve, it will be
necessary to limit the travel of the disc and spindle to the required lift of the valve which is shown in
table-1 Refer to Figure 18.
The lift of the valve is shown asA. This is the distance from B which is lift stop in the cover plate and
C which is the lift stop collar.
Before assembling the valve check the dimension from the face of the cover plate to the cover plate
lift stop B.Also check the dimension from the top of the valve body to the face lift stop collar C.
By adding these two dimensions the lift will be determined.
To decrease lift remove the cotter pin D and rotate the lift stop collar counter clockwise. To increase
lift, rotate lift stop collar clockwise.(replace cotter pin after each adjustment)
Rotating the lift stop collar one notch moves the collar approximately 0.254 mm (0.010 in). One full
turn of lift stop collar is l.587 mm (1/6 in.).
The lift stopmust be adjusted to the rated lift marked on the name plate plus an additional amount as
per table 1.
-ifirO
ec
gnirrewoL
otredloH
nitaes
sehcton
)AnmuloC(
gnirreppU
otredloH
nitaes
sehcton
)BnmuloC(
1 7 01
2 8 21
3 21 61
4 21 61
5 21 61
6 03 54
7 03 54
Q 03 54
8 73 54
R 83 74
27
The additional lift is to compensate for heated condition of the lower spindle when valve is in
operation.The following Table indicates bore diameter and-lift:
TABLE: 1LIFT SETTING DIMENSIONS
To complete the assembly of the valve, place lower spring washer (016) over spindle (046) and
lower into position on lower spindle bearing. Place spring (011) over spindle and gently lower until
firmly seated on lower washer (016). Place upper spring washer (012) over spindle and seat into
spring making sure arm of upper washer engages yoke rod (009). Place yoke and spring adjuster
with locknut as an assembly (008,101,102) over spindle (006) and both yoke rods (009) and lower
until Spring adjuster (101) contact upperwasher (012).
Install two yoke nuts (231) and pulldown evenly until made up tightly on yoke (008), with yoke in
full contact with yoke rod shoulders.
Install release collar ( 131 ) on top of spindle (016)and thread clockwise until release collar is fully
engaged on spindle thread.
Install cap (126) with drop Iever (127) over release collar (131) and seat firmly into place on yoke
(008). Install top lever (128) in cap (126) and insert pin (130) through top lever and cap holes.
Adjust release,collar downward until it clears top lever by 1.587 mm (1/16 in.) to 3.175 mm (1/8
in). Remove Iever pin (130)) top lever (128) with cap (126). Insert cotter pin (185) through release
collar slots ad spindle and spread cotter pin ends.
Reassemble cap (126) with drop lever(127),top lever (128),top lever pin (130) and then install
cotter pin to lock top lever pin in place.
v. Overlap adjustment
The overlap collar is a secondary adjustment point for blowdown control. It is utilized in conjuction
with upper adjusting ring , in no case should the overlap collar be used exclusively for blowdown
setting without first giving due adjustment attention to the upper adjusting ring.
The overlap collar is moved downward to shorten blowdown and upward to lenghten blowdown.
Orifice
Bore
Diameter
Mm(in.)
Rated lift
Mm (in.)
Additional lift
Recommended
Mm(in.)
1 28.6(1.125) 7.16(0.282) 0.254(0.010)
2 34.3(1.350) 8.59(0.338) 0.508(0.020)
3 45.7(1.800) 11.43(0.450) 0.762(0.030)
4 57.2(2.250) 14.30(0.563) 1.270(0.050)
5 52.4(2.062) 13.13(0.517) 1.016(0.040)
6 76.2(3.000) 19.05(0.750) 1.524(0.060)
7,6”-Q 95.3(3.750) 23.83(0.938) 1.778(0.070)
4”-Q 100.3(3.948) 25.02(0.985) 1.778(0.070)
8 108.0(4.250) 27.00(1.063) 2.032(0.080)
R 114.7(4.515) 28.68(1.129) 2.286(0.090)
28
dada
29
After final setting , be sure to lock the overlap collar in position by installing the cotter pin, and
sealing wire.
The overlap collar is marked with four scribe lines placed in such a position that when the lower
scribe line is even, or on the same plane with the top floating washer, the angle on the lower end of
the overlap collar is on the same plane with the lower floating washer. See Fig.19
From this position, the overlap is to be set according to Table 2. (This is a starting position only).
As reference each notch advances the overlap 0.254 mm (0.010 in.) and each scribe line is one
complete turn of the overlap collar or 1.587 mm (1/16 in.)
As a starting position of the overlap use Table-2 for bore diameter and overlap dimension. After
setting overlap, lock overlap collar (054) in place with cotter pin (184).
On some smaller valves it may be required that a mirror be used for locating the overlap scribe
lines.Should this prove not possible, disassembly of thre top works and spring washers will be
required.
An approximate guide to further adjustment positioning of the overlap collar in making final
blowdown adjustrment would be as follows:
Orifice Movement of Overlap Collar
1,2 & 3 May not need further adjustment. If needed , move I notechat at time.
4 & 5 First adjustment 5 notches subsequent adjustments 2-3 notches each time.
6 First and Subsequent adjustment ,5 notches each time.
7,Q,8&R First and subsequent adjustment, 50-60 notches each time.
THE OVERLAPCOLLAR POSITIONS SHOWNARE FINALFACTORYSETTINGS BUTONLY
STARTING POSITIONS FOR FIELD SETTING OF BLOWDOWN, FURTHERADJUSTMENTS
MAY BE NECESSARY.
TABLE 2
OVERLAP SETTING DIMENSION
o rific e B o re d ia m e te r
M m (in .)
O v e rla p
M m (in .)
1 2 8 .6 (1 .1 2 5 ) 1 .5 2 4 (0 .0 6 0 )
2 3 4 .3 (1 .3 5 0 ) 1 .7 7 8 (0 .0 7 0 )
3 4 5 .7 (1 .8 0 0 ) 2 .0 3 2 (0 .0 8 0 )
4 5 7 .2 (2 .2 5 0 ) 2 .5 4 0 (0 .1 0 0 )
5 5 2 .4 (2 .0 6 2 ) 2 .2 8 6 (0 .0 9 0 )
6 7 6 .2 (3 .0 0 0 ) 3 .3 0 2 (0 .1 3 0 )
7 ,6 ”-Q 9 5 .3 (3 .7 5 0 ) 4 .0 6 4 (0 .1 6 0 )
4 ”-Q 1 0 0 .3 (3 .9 4 8 ) 4 .0 6 4 (0 .1 6 0 )
8 1 0 8 .0 (4 .2 5 0 ) 4 .5 7 2 (0 .1 8 0 )
R 1 1 4 .7 (4 .5 1 5 ) 5 .0 8 0 (0 .2 0 0 )
30
8. HYDROSTATIC TESTING AND GAGGING
8.1 During any hydrostatic test all safety valves on the unit must be gagged. This gagging
procedure prevents the possibility of damage of the safety valve internals in the event that the test
procedure exceeds the safety valve set pressure.
When valves are subjected to working hydrostatic tests not exceeding the set pressure of the low set
valve, valves may be gagged rather than using hydrostatic test plugs. For higher pressures hydrostatic
plugs should be used and valves should be gagged.
ProbablythemostcommonsourceofSafetyValvetroubleisovergagging.During Hydrostatic
Testing and Safety Valve Setting Gags should be applied only hand tight. During setting,over
gagging will also cause damage to the seating surface and the resultant Ieakage. In applying gags
remember that the valve spring will hold the valve closed against its set pressure. The additional
gag load applied should be only enough to insure that the valves do not lift at the expected over-
pressure.
Gags should never be applied when the boiler is cold. The spindle of the safety valve expands
considerably with the temperature increase as pressure is raised. If it is not free to expand with this
temperature change it may become seriously bent.
Boiler pressure should be brought up to within 80% of the pressure of the low set valve before applying
thegags.
Tightenthegagsofdrumandsuperheatervalveswithonlyalightforceappliedtothegagstem.
Reheater valvesrequireagreaterforceappliedtothegagstemtoholdthevalveclosedduringhydrostatic
test.
Application of Test Gags (All Pressures)
i. Refer to Fig. 20. Remove top lever pin (130), top lever (128) then loosen cap screw (238)
remove cap (126) and Drop lever (127) as an assembly. The release collar (131) is fixed to
spindle (046) by means of a cotter pin(185). Note that the release collar(131) does notquite
engage top of spring adjuster (101). See fig for details or release collar position.
ii. Center the test gag stem on the exposed end of the spindle (046) and hook the legs of gag under
the sides of the yoke as shown in Fig.23
DO NOTAPPLY THE GAG LAOD UNTILTHE BOILER HYDROSTATIC PRESSURE IS
EQUALTO 80%OFTHE PRESSURETO WHICH THE LOWSETVALVE ISADJUSTED.
iii. Apply the gag load by turning the gag stem clockwise.
Any attempt to pinch off the leakage through the valve without first lowering the hydrostatic pressure
is liable to result in damage to the valve seats.
If the gag on the valve has not been tightened sufficiently, the valve will leak and sometimes the
leakage is accompanied by “Sizzling” sound.
If this occurs the hydrostatic test pressure should be reduced until the valve becomes tight and then
gag should be tightened further.
This procedure must be followed exactly since it is very difficult to stop the leak by additional
gagging once it has started.
iv. After the hydrostatic test is completed,the gags should be removed when the hydrostatic
pressure has been reduced to 85% to 90% of the pressure of the low set valve.
31
UNDER NO CIRCUMSTANCE SHOULD THE GAGS BE LEFT ON VALVES WITH NO
HYDROSTATIC PRESSURE ON THE SYSTEM NEVER TRY TO ARREST LEAKAGE
BY FURTHER TIGHTENING THE GAG.
Nomenclature List: Fig. 20
002 Base
003 Seat Bushing
004 Inlet Neck
008 Yoke
009 Yoke rod
011 spring
012 Upper Spring Washer
016 Lower Spring Washer
026 Disc
028 Disc Holder
029 Disc Collar
031 Guide
036 Upper Adj.Ring
037 Upper Ring Pin
038 Lower Adj.Pin
FIG 20(A)
FIG 20
32
039 Lower Ring Pin
046 Spindle
052 Lift Stop
054 Overlap Collar
056 Cover plate
057 Lower Washer Retainer
058 Lower Floating Washer
059 Lower washer Retaining Pin
061 Top Plate
062 Upper Washer retainer
063 Upper Floating Washer
064 Upper Washer Retaining Pin
101 Spring Adjuster
102 spring Adjuster Lock Nut
105 Service Port Plug
126 Cap
127 Drop Lever
128 Top Lever
129 Drop Lever Pin
130 Top Lever Pin
131 Release Collar
182 Disc Collar Cotter Pin
183 Lift Stop Cotter Pin
184 Overlap Collar Cotter Pin
185 Release Collar Cotter Pin
226 cover plate stud
229 cover plate nut
231 Yoke Rod Nuts
232 Lower Yoke Rod Nuts
237 Retainer screw (Top Plate)
238 Cap Set Screw
8.2 Hydrostatic test plug removal
FLANGED INLET SAFETY VALVES SHOULD BE REMOVED FROM THE BOILIER
DURING THE HYDROSTATIC TESTS AND BOILER NOZZLES BLANKED OFF.
Welded inlet valves are fitted with hydrostatic test plugs.
These valves are identified by a White Caution tag with red Ietters attached to the internal plug by
wires extending through the drain hole in the valve body See Fig.21.
33
8.2 Hydrostatic test plug removal
FLANGED INLET SAFETY VALVES SHOULD BE REMOVED FROM THE BOILIER
DURING THE HYDROSTATIC TESTS AND BOILER NOZZLES BLANKED OFF.
Welded inlet valves are fitted with hydrostatic test plugs.
These valves are identified by a White Caution tag with red Ietters attached to the internal plug by
wires extending through the drain hole in the valve body See Fig.21.
The hydrostatic plugs are placed in the bore of the valve, inside the sealing surface. Their purpose is
two-fold. First they effect closure at a point differing from the seating surface of the valve so that if
the valve is lifted on hydrostatic test, the seating surface will not be as liable to become damaged.
Second, by raising the spindle of the valve and increasing spring compression, the set pressure of
the valve is increased to a point where the valve will not leak at one and one-half times design
boiler pressure. It is not necessary to gag safety valves tightly when hydrostatic plugs are used.
These plugs must, of course, be removed from the valves prior to placing the boiler in service.
However, they should be stored carefully and reinstalled whenever a hydrostatic test exceeding the
low set valve pressure is conducted.
Hydrostatic plugs can be Ieft in the valve until steam blowing is over.
When hydrostatic plugs are installed in the Valves, the disc is removed and clipped in
preservative, then packed in a box. The package is then inserted into the valve outlet and taped to
the floor of the valve body.
FIG.21: CAUTION TAG
FIG.22: HYDROSTATIC TEST PLUGINASSY
34
iv. Then lift the spindle, springs, spring washers, cover plate ,disc and disc holder as an
assembly out of the valve.
v. Remove ‘seal peel’ preservative from disc thoroughly clean disc seat with a clean cloth.
vi. Lubricate spindle tip with “Molykote G” and assemble disc and disc holder to spindle by
turning disc clockwise until dropout thread disengages.
vii. Place complete upper assembly in valve body
viii. Install and tighten Yoke Rod Nuts and Cover plate nuts.
ix. Remove cotter pin from release collar and position release collar so that 3.175 mm(1/8in.)
of clearance is visible between Lifting fork and release collar then install cotter pin through
the spindle at the upper hole.
x. Install lifting gear.
FIG3: APPLICATION OF TEST TAG
9. FIELD SERVICE AND REPAIR
9.1 Factory Setting Vs. Field Setting
Every Safely Valve is set and adjusted on steam before shipment from the factory. Blowdown
adjustments are made is carefully and accurately as possible on the factory test boiler. However
it must be recognized that actual field operating conditions may vary considerably from factory test
conditions.
Conditions beyond the manufacture’s control that affect safety valve operation are:
i. Quantity of steam being discharged through the valve, i.e. the actual installation capacity
exceeding that of the test boiler, thus permitting the valve to flow its full rated capacity.
ii. Quality of steam being discharged.
iii. Discharge piping stresses and back pressure.
iv. Ambient temperature.
v. Shipping or storage damage.
vi. Improper gagging.
vii. Improper bolting of flanges
viii. Damage due to foreign material in the steam.
xi. Damage, during disassembly and assembly in the field
35
Final Safety Valve adjustments made on the actual installation is the best means of ensuring that the
valves perform in compliance with the applicable code requirements.
9.2 Recommended Spare parts for 1700 Safety Valves
TABLE 5
Class I & II parts are most frequently replaced due to wear and tear in normal service. Parts covered
in Class III and IV are seldom replaced and may be stocked, based on customers experience or
requirements.
Refer to Fig. 20 for part name. All others required information will be found stamped on the name
plate attached to the body of the valve.
In addition, the serial number is stamped on the top edge of the outlet flange. Be sure to include the
one or two letters preceding the figures in the serial number
ssalc emaNtraP
relioBlacitirC-buS
)raB7.022-isp0023rednU(
noitceStaeheRretaehrepuSmurD deeN
ytilbaborP.pmeTdna.rPteSepyT/emaS/trap/ytQ
egarevocfossalCezis
ecivreSnievlav
I csiD.1 4/11/11/1
gniR.jdA.2
)reppU(niP
%074/11/11/1
niPgniR.jdA.3
)rewoL(
4/11/11/1
gniR.jdA.4
)reppU(niP
4/14/14/1
niPgniR.jdA.5
)rewoL(
4/14/14/1
II redloH.6 %584/14/14/1
eldnipS.7 6/12/12/1
ediuG.8 4/14/14/1
ralloCpalrevO.9 6/14/14/1
ralloccsiD.01 6/14/14/1
potStfiL.11 6/14/14/1
III gnirpS.21 6/16/16/1
gnirpS.31
)2(rehsaW
%596/tes/16/tes/16/tes/1
noisserpmoC.41
wercS
6/14/14/1
palrevO.51
niPralloc
6/14/14/1
ralloCcsiD.61
niP
6/14/14/1
niPpotStfiL.71 %996/14/14/1
noisserpmoC.81
tuNwercS
6/14/14/1
etalPpoT.91
swercS
4/tes14/tes14/tes1
36
The table 5 gives the recommended spares quantity required based on valve location. Spares may
be ordered by giving:
1. Part Name
2. Quantity along with the valve details.
3. Size
4. Type
5. Temp. Class
6. Serial No.
Eg.3" 1759 WB: Sl.No. Disc-2 Nos.
9.3 Maintenance TOOLs and Supplies
LAPPING TOOLS:
Thc following tools are required for proper maintenance of Safety Valve seats:
Ring Lap-The ring lap is used for lapping the nozzle and disc seats.
Lapping Plate-The lapping plate is used for reconditioning the ring laps. Only one 275mm (11”)
diameter plate is required for all sizes of ring laps.
Lapping Compound -Lapping compound is used as a cutting medium for lapping and polishing the
seats and bearing surfaces in Safety Valves.
i. *RING LAPS (See Note 1).
**Valve Orifice Lap Tool No.
(See Note 2) Part No.
1 1672806 44.54151.00
2 1672807 44:54152.00
3 1672808 44.54153.00
4 1672810 44.54155.00
5 1672809 44.54154.00
6 1672811 44.54156.00
7 & Q 1672812 44.54157.00
8 & R 1672814 44.54159.00
NOTE 1: One set of (3) Ring Laps is recommended for each orifice valve in service to assure ample
flat laps are available at all times.
NOTE 2: Valve Orifice number is third digit of the valve type number,eg a 1737WA valve has a
orifice no. of 3.
ii. Resurfacing Plate 275mm( 11 “) Diametre
37
iii. Lapping Compounds
Grift Lapping Function
320 General
500 Finishing
1000 Polishing
iv Lubricant
Location Lubricant
Bearing Points
a. Spindle/Disc
b. Spring adjuster top
Spring Washer Molykote “G”
c. Spindle/Bottom
All Threads Molykote “G”
All Nut Contacts
Faces Molykote “G”
v. Roto-Lap Machines
vi. Reseating Machine
10. GUIDELINES FOR THE STEAM TESTING OF BOILER SAFETY VALVES
Please take five minutes to read this short guideline. Implementing the following procedures will
benefit your company in good valve performance, reduced labor time and fuel savings.
Mechanical
1. We highly recommend a preliminary test at reduced pressures of the boiler valves with our
1566 hydroset prior to steam.
Savings in fuel and time will easily justify this step.
2. Only calibrated test gauges should be used for testing safety valves.
Gauges not calibrated can cause problems with operating pressure later or even necessitate
the retesting of all the safety valves.
3. Gage for each valve should be available and in good condition.
4. Discharge piping has to be inspected for binding on the valves,supports and welds on
piping.
Binding of the discharge could make the valve hang up on closing. Insufficient welds and
supports could cause the dicharge piping to fly off during valve activation.
5. A rope approximately 5 to 7 metres with a hook one end should be attached to the valve
lifting lever before activation.Should the valve chatter or not lift at set pressures, the rope
can pulled, Eliminating chatter and stop over pressure of the vessel.
6. Have the correct tooling available.
Looking for tools means lost lime. Having incorrect tools can cause damage to compression
screws and other valve parts.
7. Establish a good communication system between the boiler and control room.
38
This eliminates mistakes that could be dangerous and time consuming.
Operational
1. If the unit has an electric pilot operated relief valve “Electromatic”, place this valve in
operation first.
Since safety valves are tested one at a time and the other valves are gagged, the pilot actuated
relief valve will increase the safety factor of the unit while testing. Pilot operated valves can
be actuated from the control room if some emergency should develop during the controlled
burner firing associated when tests are being conducted. The electromatic will help clean
contamination from system.
2. The Drum valve should be tested first
Possiblities of valve part damage because of “girl blasting” are greater on superheated valves
in contrast to the drum valves. If a super heated valve is gagged after seat damage while
testing of other valves continues, the total valve damage will most likely be increased.
Tempratures of the boiler increase during the testing cycle of the Drum Valves. Consequently
higher temperature steam will be available for testing the Superheater valves and produce
more accurate results.
Keep water level down as low as possible while testing drum valves.
If drum valves level is high the SafetyValve may be stugged with water causing a long
blowdown and possibly damage the valves
4. Pressure should be brought up evely and fairly rapid rate
A slow raise in pressure will increase the simmer of the valve possibly causing the valve to
life erractically. We recommended 2 to 3 kg/cm2 per minute increase in pressure during
testing to be optimum.
Should a burner or other systems fail when pressure is near the set pressure of the valve,
drop boiler pressure al Ieast 10 percent below set pressure before raising boiler pressure
again.
Holding boiler pressure near the set pressure of the valve will induce simmer, possibly causing
the valve to lift erratically.
6. Drop pressure after a valve has lifted to a safe level before taking the gag off the next valve
or making-valve adjustments.
20 percent of the valve set pressure will assure the nongagged valve will not lift prematurely.
7. If a valve has to be lifted several times, a cooling off period will be necessary.
For outside or inside valve installalion, 25-30 minutes is sufficient: If this cooling period is
not maintained, erratic operation of the valves can be expected.
8. If the valves have not been tested with the hydroset prior to the steam actuation, it is
recommended to hand lift the valves before the actual steam pop.
Hand lifting the valves will show that the valves are functional Furthermore, it will help to
warm up the valves.
39
Safety
For the protection of persons in testing be valves, a few simple steps can, prevent accidents
and injury.
1. Have only people on the boiler absolutely necessary for the testing of the valves.
2. Rope off the area where valves are going to be tested.
3. When working on the valves, wear glooves
4. All personnel on the boiler are to wear eye and ear protection.
5. Warn people on the plant site that valve testing is being performed.
The recommendations we have made represent many years of field experience. We hope you can
implement some or all of them. Hopefully, you will have a good start up.
INDEX

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Bhel STEAM safety valve_1700_series

  • 1. SAFETY VALVE (1700 SERIES) Pub.No 7056 Bharat Heavy Electricals Limited Tiruchirapalli
  • 2. 2 CONTENTS INTRODUCTION SAFETY PRECAUTIONS DESIGN FEATURES AND CONSIDERATION HANDLING, STORAGE AND PRE -INSTALLATION CHECK LIST FOR STORAGE, ERECTION AND COMMISSIONING RECOMMENDED INSTALLATION PRACTICE OUTDOOR SAFETY VALVE INSTALLATION INDOOR SAFETY VALVE INSTALLATION GENERAL CONSIDERATIONS OPERATION FIELD SETTING POPPING POINT ADJUSTMENT RING ADJUSTMENT REFER PAGE 9 (A) LOWER RING ADJUSTMENT UPPER RING ADJUSTMENT BLOWDOWN ADJUSTMENT SEALING VALVES AFTER TEST DISASSEMBLY WITH RETENTION OF SPRING SETTING DISASSEMBLY TO COMPONENT LEVEL MAINTENANCE LAPPING PROCEDURE CHECKING SPINDLE RUN-OUT RE-ASSEMBLY REASSEMBLY WHEN SPRING LOAD RETAINED REASSEMBLY OF VALVE FROM COMPONENT LEVEL LOWER ADJUSTING RING UPPER ADJUSTING RING
  • 3. 3 DETERMINING RING POSITION WITH VALVE UNDER PRESSURE LIFT ADJUSTMENT OVERLAPADJUSTMENT HYDROSTATIC TESTING AND GAGGING HYDROSTATIC TEST PLUG REMOVAL FIELD SERVICE AND REPAIR FACTORY SETTING VS. FIELD SETTING RECOMMENDED SPARE PARTS FOR 1700 SAFETY VALVES MAINTENANCE TOOLS AND SUPPLIES GUIDELINES FOR THE STEAM TESTING OF BOILER SAFETY VALVES
  • 4. 4 INTRODUCTION The 1700 series safety valves are manufactured in India by Bharat Heavy Electricals Limited,Trichirappali under the licence agreement with m/s.Dresser IndustrialValveDivision,U.S.A. These valves are intended for service in power boilers at pressures upto 213 barg(3090psig) and temperatures upto 604.4o C(1120o F). Thesee valves are manufactured, tested and certified as per Indian Boiler Regulations. Bharat Heavy Electricals Limited Tiruchirapalli-India
  • 5. 5 SAFETY PRECAUTIONS * Do not go near discharge side of a safety valve * Body drain and cover plate vent must be piped to a safe area. * If left open,steam will escape and present a burn hazard to personnel near the valve. * Always gag a safety valve before making ring adjustments. * When pulling hand lever for inspection purposes,a rope should be attached to the handle of sufficient length (minimum 6 to 10m long) to protect the operator from escaping steam, dust, fly ash etc., * Exercise caution when examining a safety valve for audible leakage. SUPER HEATED STEAM IS NOT VISIBLE. * Safety valves should be mounted to provide adequate access, 3600 around the valve plus overhead,for disassembly and maintanence. * Use ear-muffs during the adjustment of valves. * Use hand gloves during adjustment of valve in the hot condition.
  • 6. 6 DESIGN FEATURES AND CONSIDERATION (1700 Series) 1.1 Body and Neck Materials All pressure retaining parts, with the exception of reheat valves rated to 62.1 bar (900 psi) and lower, are made of forged materials. Forged welded inlet neck valves have the three-piece weld construction; flanged inlet valves and cast neck welded inlet valves have a top-inserted seal-welded seat bushing. 1.2 Service Life For most service conditions, pressure retaining parts and parts subject to mechanical stresses, such as valve necks, yoke rods, etc., are designed for a service life equivalent to the boiler and well in excess of the requirements of the Power Boiler-Code and IBR. 1.3 Thermal Compensation The valve has been designed to provide temperature compensation. Minor adjustments may be required in some extreme temperature variation conditions. 1.4 Thermodisc The thermodisc design in providing for the rapid equalization of temperature around the valve seat, provides a degree of tightness far above that offered by competitive valves. Thermodiscs are now giving excellent results upto 379.3 bar (5500 psi) and 621°C (1150°F) 1.5 Blowdown. The Safety Valve can be set with 3% attainable blowdown certified by the National Board of Boiler and Pressure Vessel Inspectors. 1.6 Operating Gap Safety Valves are tested and proven tight for operating gaps of 5%,operating gap being defined as the difference between operating pressure and the low set pressure valve. Although tightness is a function of design, it should be realised that with smaller operating gaps it is also necessary to increase maintenance. Increases in incidents of valve lift, simmer, etc., can be expected because of less allowance for system pressure transients and other unidentified variables. 2. HANDLING, STORAGE AND PRE -INSTALLATION Safety valves should be stored in a dry environment to protect them from the weather. They should not be removed from the skid’s or crates until immediately prior to installation. Flange protectors end covers and sealing plugs should also be installed until just prior to installation. When Safety Valves are uncrated and the flange protectors removed immediately prior to installation, meticulous care should be exercised to prevent dirt and other foreign materials from entering the inlet and outlet ports while bolting or welding in place. Ensure the disc is available. Identify the disc and store it safely with D.U sequence required for assembly. Check for disc identification dimension before assembly table 4. The valve, either crated or uncrated, should always be kept with the inlet down i.e., never laid on its side, to prevent misalignment and damage to internals. Keep valve on cradle after removing from crate. Uncrated valves should be moved or hoisted by wrapping a chain or sling around discharge neck, then around upper yoke structure in such a manner that will insure the valve in vertical position during lifting i.e., not lifted in horizontal position. Never lift the full weight of the valve by the
  • 7. 7 lifting lever. Never hook to the spring to lift. Figure shows the correct way of lifting the valves. Crated valves should always be lifted with the inlet downwards. Safety valves, either crated or uncrated, should never be subjected to sharp impact. This would be most likely to occur by pumping or dropping during loading or unloading from a truck or while moving with a power conveyor, such as a fork lift truck. While hoisting to the installation, care should be exercised to prevent bumping the valve against steel structures and other objects. 2.1 Check list for Storage, Erection and Commissioning i. Check for tag No.or D.U.No. as per packing slip. Non-availability or discrepancy must be informed to the manufacturing unit. Check for test certificates for each safety valve. ii. check whether the inlet size, orifice, material grade, set pressure etc.are as per the boiler O&M Manual. iii. check that the seals are intact on ring pin, spring adjuster and overlapcollar. Check for transit damages, if any. iv. Ensure that the end covers are kept in position and removed only just before erecting in place. Meticulous care should be taken to ensure dirt or foreign particles do not enter into the inlet or outlet of the valve. v. Ensure the valves are stored in crates on sleepers in a covered area with the inlet side downwards. Valves should never be laid on the side to avoid damage to internals. Erection vi. Ensure that the disc is available, identify and keep in a safe place for final assembly as per D.U. sequence. Identify and hand over the Hyd.test plugs to the user after the Hyd.test is completed. a. Ensure proper preservation for exposed surfaces of valve and service tools for long storage. b. Ensure the valves are never subjected to impact by bumping or dropping during loading and unloading and disassembly and assembly of valve. c. Do not lift valve with lever or spring. Sling valve as per O&M. vii. Valves should be erected with spindle vertical within a tolerance of ± 1° from the vertical plane. viii. Ensure proper pre-heating and post heating,stress relieving and NDT procedures are followed when welding to the stub. ix. Ensure that the vent pipe is separately supported and does not touch the drip pan unit and that there is sufficient allowance for expansion in horizontal and vertical directions. x. Ensure the cover plate vent and drain are connected with pipe of adequate size to safe locations. xi. Extend insulation of vent pipe over roof to avoid rain water collection into drip pan. Insulate the inlet and body upto the cover plate. xii. After hydrostatic test of boiler, remove hydro test plug and ensure dice is replaced and valve reassembled without affecting setting as per O&M. Commissioning xiii. Use calibrated pressure gauges for safety valve floating. Float the lowest set safety valve first, gag the valve after setting is over and float the next higher set valve and so on till all valves are floated and checked for the set pressure within ± 1% tolerance level.
  • 8. 8 xiv. Try to achieve the setting within a minimum no. of pops (about 3 pops). xv. Check that blowdown is within 5%. xvi. Apply gag load finger tight in hot condition to avoid spindle bending. xvii. Remove gags after floating of safety valves. xviii. Check and ensure sufficient approach and maintenance space all around the valve. xix. Proper structures for mounting the slings or pulley blocks are necessary for maintenance purposes. Same may be checked during installation itself. xx. After the valves are set in the field, release collar should be taken up and locked with cotter pin such that min.gap of 3.2 mm (1/8”) is retained between the collar and top lever. 3. RECOMMENDED INSTALLATION PRACTICE i. The safety valve or valves shall be connected be valve or valves shall be connnected to the boiler independent 0f any other connection, and attached as close as possible to the boiler, without any unnecessary intervening valve or fitting. Such intervening pipe or fitting shall not be longer than the face-to-face dimension of the corresponding tee fitting of same diameter and pressure. Every safety valve shall be connected so as to stand in an upright position with spindle vertical. ii. The opening or connection between the boiler and the safety valve shall have atleast the area of the valve inlet. No valve of any description shall be placed between the required safety valve and the boiler nor on the discharge pipe between the safety valve and the atmosphere. When a discharge pipe is used, the cross-sectional area shall not be less than the full area of the valve outlet of the total of the areas of the valve outlets discharging there into.It shall be as short and straight as posssible and so arranged as to avoid undue stresses on the valve or valves. All safety valve discharges shall be so located or piped as to be carried clear from running boards or platforms. Ample provision for gravity drain shall be made in the discharge pipe or near each safety valve or safety relief valve, and where water or condensation may collect. Each valve shall have an open gravity drain through the casing below the level of the valve seat. For iron and steel-bodied valves exceeding 63.5 mm (2-1/2") size, the drain hole shall be tapped not less than 9.5 mm (3/8") pipe size. iii. If a muffler is used on a safety valve or safety relief valve, it shall have sufficient outlet area to prevent back pressure from interfering with the proper operation and discharge capacity of the valve. The muffler plates or other devices shall be so constructed as to avoid a possibility of restriction of the steam passages due to deposits. When a safety valve is exposed to outdoor elements which may affect operation of the valve, it is permissible to shield the valve with a satisfactory cover. The shield or cover, shall be properly vented and arranged to permit servicing and normal operation of the valve. iv. Safety valves may be attached to drums or headers by welding provided the welding is done in accordance with Code requirements. 3.1 Outdoor Safety Valve Installation Safety Valves operating under the best possible conditions of favourable operating gap, relatively stable ambient temperatures, absence of dirt and in relatively still air, will provide the maximum degree of safety, tightness and dependability. When a safetyvalve is installed in a location such as out of doors, it is exposed to wind, rain, snow, ice, dirt and varying temperatures.
  • 9. 9 The following recommendations are made for proper protection to insure that operational dependability can be restored to a level near that of the valve installed under ideal conditions. The inlet neck of the safety valve and safety valve body, upto the bottom of the cover plate. should be insulated. The exterior surface of any such insulation should be weather proofed by any suitable means. In addition to maintaining a more even temperature with in the valve body, during widely fluctuating ambient temperatures, this insulation will effectively reduce thermal stresses due to high temperature gradients through the walls of the safety valve nozzles. Even in tropical latitudes, insulation should be applied since safety valves installed in outdoor locations in these areas are subject to hurricane conditions. Spring covers should be used to stabilize as nearly as possible the temperature of the spring and also to prevent the accumulation of dirt, ash, and ice between coils of the spring.. Lifting gear covers should be installed to prevent ice, dirt and fly ash from accumulating in areas inside the safety valve cap. 3.2 Indoor Safety Valve Installation In-door-valve installations should have inlet necks insulated only upto the underside of the valve body Considerations should be given to ambient temperatures of greater than 38.8°C (100°F;) because of possible set point change which may occur due to higher ambient temperatures. 3.3 General Considerations i . Excessive pressure loss at the inlet of the safety valve will cause extremely rapid opening and closing of the valve, which is known as “chattering” .Chattering may result in lowered capacity as well as damage to the seating surface of the valve. Severe Chattering can also cause damage to other parts of the valve. The following recommendations will assist in eliminating the factors that produce chatter. a. The area of the inlet nozzel should he atleast equivalent to the inlet area of the safety valve and that nozzle should be short as possible. b. Inlet nozzle corners must be rounded to a radius of not less than 1/4 of the diameter opening. c. Pressure drop to the inlet of the valve should not be greater than 50% of the expected blow down of the safety valve. d. To eliminate the effects of a phenomena known as sonic vibrations, the following recommendations are made. Safety valves should be installed atleast eight to ten pipe diameters down stream from any bend in a streamline. This distance should be increased if the direction of the change of the steam flow is from vertical upwards to horizontal in such a manner as to increase density of the flow in the area directly beneath the safety valve nozzles. Safety valves Should not be installed closerthan eight to ten pipe diameters either upstream or downstream from diverging or converging “Y” fittings In cases where piping configuration renders thc two above recommendation impractical or impossible, the downstream corners of the nozzle inlets should be rounded, leaving the upstream corners square. The nozzle entrance should be rounded so that the radius at the downstream corner will be equal to one-fourth of the nozzle diameter. The radius should be reduced gradually leaving only a small portion of the upstream corner sharp. The safety valve nozzle should never be installed in a steam line in a position directly opposite a branch line of equvalent size.
  • 10. 10 ii. Excessive steam line vibrations are known to produce shifts in safety valve set pressures. Results of sizable vibrations will be to introduce possible chatter with ultimate damage to the valve in addition to reduced capacity Such line vibration should be examined for optimum valve performance. iii Exhaust, drain and cover plate vent piping must be installed so that they will not impose under stresses on the safety valve .These stresses can produce distortion and Ieakage at pressures below the set point.The following recommendations should be noted: a. Discharge piping should not be supported by the valve. The maximum weight on the outlet of the valve should not exceed the weight of a discharge flange, elbow and drip pan unit. b. Clearances between the valve exhaust piping and the discharge stack should be sufficient to prevent contact when considering thermal expansion of the boiler , valve , discharge stack and increased stack movement due to vibration and temperature when the valve is relieving. c. Flexible metal hoses if used to connect safety valve outlets to discharge slacks, must have sufficient length and must be designed and installed in such a manner that they will not become “solid” in any position of the valve. Better results are obtained if the hoses are installed so that they will permit movement by bending, rather than by stretching and compressing along their length. iv. Steam flowing vertically out of the discharge elbow produces a downward reaction on the elbow, in proportion on the quantity of steam flowing and its velocity. In large, high capacity valves this force can equal several thousand kilograms and can produce severe stresses in the valve necks. The bending stresses are determined by the amount of the reactive forces, combined with the moment arm, or horizontal distance between the vertical centreline of the valve and the vertical center line of the outlet elbow. v. In no case should discharge piping be of a smaller size than the valve outlet .The length of the discharge stack will govern its size and with increased lengths, stack diameters will increase. This will prevent blow back from the discharge stack. Excessive water being pulled through the valve will also produce a blow back under certain conditions and should be investigated prior to faulting the discharge stack. vi. For optimum performance, safety valves must be serviced regularly and maintained. So that servicing can be properly handled safety valve should be located for easy access. Sufficient working space should be provided around the safety valve to permit access to adjusting rings. If two or more safety valves are located close together, the outlets should be parallel, to offer as much protection as possible to personnel repairing or working close to the safety valve. Cross beams may be provide above valve centre line for easy disassembly of safety valves. vii. For valves being installed that are tested for set pressure with the use of a hydroset, it should be realised that only the set pressure is being verified. Other factors such asblow down, lift, reaction force, proper inlet welding, proper discharge stack sizes and effects of thermal expansion cannot be determined. viii. Because foreign material passing into and through a safety valve may damage it, the system on which the valve is tested and finally installed must also be inspected and cleaned. New systems, especially, are prone to contain welding beads, pipe scale, and other foreign material which are inadvertently trapped during construction and destroy the sealing surfaces the first few times the valve opens. Wherever possible, the system should be purged thoroughly before the safety valve is installed.
  • 11. 11 It is recommended that the safety valve be isolated during hydrostatic testing of the boiler either by blanking off the valve, gagging the valve, or installation of hydrostatic test plugs. ix. For weld-end inlet valves, completely assembled valves may be installed with out necessity for disassembly. Vertical alignment should be within ± 1° from a vertical plane. During welding, where possible, the valve neck should be insulated to reduce thermal effects. When stress relieving, the same will apply. In all cases the valve neck should be insulated atleast upto the inlet neck-valve body bowl juncture. x. It is of outmost importance that the gasketing used be dimensionally correct for the specific flange and that if fully clears the valve inlet and outlet openings. Gasket, flange facings, and bolting should meet the service requirements for the pressure and temperature involved. When installing flanged inlet valve, the flange bolts must be pulled down evenly in order to prevent body distortion and consequent misalignment and leakage. xi. On new installations, during initial setting of safety valves there is a possibility of damaging the superheater valve seat due to foreign matter, such as mill scale, weld spatter and beads, etc., being drawn into the steam flow. This foreign matter batters and cuts the seats of the valve although damage to the bushing seat is usually considerably less than to the disc seat. This type of damage causes the valve to leak quite badly and generally requires that the disc be replaced and the bushing seat relapped. Before bringing the boiler down, the leaking valve should be hand-blown atleast ten times and held open for a period of one minute each time. This should clean any remaining foreign material out of the superheater and minimise the possibility of damage to the seats after overhaul, although this particular trouble sometime persists until the boiler has been operating for a considerable period of time. Drum safety valves do not, generally, draw foreign matter into the steam flow, and no difficulty of this type to be expected 3.4 Cover Plate Vent Piping The vent piping of the cover plate can be installed in one of the three ways. First, the cover plate can be piped upto the drip pan as shown in Figure 1. Second, the cover can be vented to atmosphere as in Figure 2. Third, the vent can be directed toward the discharge stack as shown in Fig.2a. Precautions should be taken to vent cover plate in such a manner that it will exhaust into a safe area to prevent injury to personnel near the valve. CAUTION: Do not plug cover plate vent hole or reduce vent hole pipe size. Precautions should be taken to prevent accumulations Foreign material or water in the vent pipe. This vent is a critical part Or the valve system for controlling valve blowdown and lift. 4. OPERATION The safety valves operate during closing with a back pressure principle, that is, the force of trapped steam on the upper side of the disc holder is utilized to assist the spring in forcing the disc back down on its seat. Reference to Fig.3 for illustration and Fig.20 for nomenclature, it will be seen that when the valve is blowing, a small amount of steam is bled from the huddle chamber (A) through holes (B) into chamber (C) and escapes to the atmosphere between floating washer (D) and overlap shoulder (E). The steam also flows through an internal orifice and out through (F). As the inlet steam pressure drops,the overlap shoulder (E) upon reaching the top of the floating
  • 12. 12 washer (D) traps steam in chamber (C), builds up pressure on top of the disc holder, and assists the spring in closing the valve. The distance from the top of the floating washer (D) to overlap shoulder (E) is therefore. ,an important function in the operation of the valve and must be correct in dimension. Table 2 gives the correct initial overlap dimension corresponding to bore size. 4.1 Field Setting All Safety valves are steam tested at the factory. Every valve is set to have a clean popping action and to reseat tightly. However, because the boiler used In setting the valves has a small capacity compared to the capacities of the valve. Slight adjustments on the actual installation are necessary to maintain proper action and blowdown. Two methods exist for field testing of valves ;use of the 1566 or 1566-2, Hydroset Unit,and full system pressure. As previously noted, the use of a hydroset unit will serve to establish Set pressure only and should not be used for establish blowdown, lift, etc., Gagging of other valve not being set generally will not be necessary; however, for setting of high set pressure valves, depending on system pressure being used, it may be required to gag the lower set valves. Boiler safety valves tests can be conducted with the unit either on or off the line.However, with the unit on the line at full load a sudden load drop could be dangerous as most of the safety valves will be gagged. Therefore, it is recommended that the safety will be tested and adjusted with unit off the line or with light load. Boiler control can then be maintained with little or no outside influence due to load change. The valves should be set within ±1% of the set pressure. Set pressure should not be changed without the permission of the manufacturing unit.Lab standard or test Gauges should be used with a minimum graduation of 0.5% of the full scale reading and accuracy of ± 0.25%.Gauges should be of sufficient range so that reading is in the middle third of the scale. Factors Which Can affect Safety valve operation are: i. Ambient temperature ii. Discharge Stack Binding against drip pan elbow. iii. Vibration of the header from upstream bends, etc., 4.2 Popping Point Adjustment To change the popping pressure of the valve remove the cap and lever assembly, loosen the locknut and turn the spring adjuster clockwise to increase pressure. After each adjustment of the spring adjuster the locknut should be tightened. The arm on top of spring washer should always be free from bearing against the yoke rod. This can be accomplished by holdingAscrewdriver between the arm and the rod to prevent any movement of the top spring washer while adjusting the spring adjuster. 4.3 Ring Adjustment Refer page 9 (a) Always gag the Safety Valve for protection, in case boiler pressure rises while making ring adjustments (See instructions for gagging). The positions of the upper adjusting ring and the lower adjusting ring are locked by means of the upper adjusting ring pin and the lower ring pin respectively. These pins are threaded into the valve body and engage notches which are cut into the rings. To adjust either ring the corresponding ring pin must be removed. A screw driver can be used to turn the rings.
  • 13. 13 Spare ring pins when supplied will be of excess length and have to be individually ground to match each valve. The tip of the pin should not touch the bottom of the ring notches. Lower Ring Adjustment Using Figure 17 and Table 3, a reference plane is established where the adjusting ring is level with the bushing seat. From this setting, factory adjustments are made by adjusting one notch downward for each 42.2 kg/sq..cm (600psi) of set pressure. Ring position should be checked prior to testing. Slight deviations from these settings are possible because of tests conducted in the plant. NOTE (THIS PROVIDES A STARTING POINT ONLY). The lower ring is used to obtain a clean popping action and to cushion the closing action of the valve. DO NOT ATTEMPT TO ADJUST BLOWDOWN WITH THE LOWER RING. The ideal position must then be found for the set of operating conditions present. If simmer is present or valve fails to lift, the lower ring should be moved upward slowly, one notch at a time to remove the simmer. The most ideal position for the lower ring is the lowest position that does not introduce simmer or a buzzing sound. In this connection, it is imperative that extreme care be used in conditioning the seat surfaces,
  • 14. 14
  • 15. 15 ensuring correct alignment, and establishing the proper clearance, so that mechanical causes of simmer will be reduced to a minimum. Upper Ring Adjustment When shipped from the factory, upper adjusting rings are set level with the bushing seat in accordance with Figure 17 and Table 3. This should be checked prior to field setting and should be regarded as a starting position only. It is possible that this position is not strictly in accordance with Figure 17 and Table 3 on some valves because of testing at the plant. The ring may be set lower than the seat level, but never before, until field tests are conducted. Starting position for blowdown check should place bottom surface of upper ring level with bushing seat. Since the bushing seat is not visible through the service ports. It is necessary to use a cross-reference relationship. Raise the upper ring until its bottom surface in level with the disc holder, which is visible through the ports. Then, referring to Table 3, Column B, lower the upper ring the required number of notches. This will place the upper ring on a plane with the bushing seat. This is the starting point for blowdown tests. Further adjustments may be necessary depending on test results. When further adjustments are required to obtain final blowdown setting, the upper adjusting ring should be moved 5-10 notches at a time as follows: Guidelines for setting and locking adjusting rings Gag the safety valve for protection while making ring adjustments. The lower and upper adjusting ring pins of any particular valve is not interchangeable. Spare ring pins when supplied will be of excess length. These pins are to be ground at site so as to match the valve under maintenance. The tip of pin should NOT touch the bottom of the ring notch (refer sketch enclosed) Also the pins should not bear against the rings. DO NOT attempt to adjust blow down with the lower ring. The upper adjusting ring should not be set below the seat level and the lower adjusting ring should not be set above the seat level. Lock both the ring pin settings using a seal wire to avoid disturbance during system/valve operation and line vibrations. FIG 3: ` SECTION ILLUSTRATING OVERLAPAND BACK PRESSURE SYSTEM
  • 16. 16 Ensure that the above settings are properly locked: Periodically check whether the pins are in their appropriate place and are effective. This can be checked through the service port ,provided in the valve body. A sketch showing acceptable ring pin positions is enclosed. Excessive line vibrations, presence of foreign particles, discharge piping stress, back pressure, reaction force etc., can lead to pin failure over a prolonged period of exposure. The ring pins being the most critical spare part, it is desirable that one pin per valve (for drum and SH SVs) and one ring per four valves (for RH SVs) is stocked as essential spares by customer. Adherence to the above aspects would eliminate cases of premature pin failure and lead to a satisfactory valve performance. To reduce blowdown -MOVE RING UP-TURN COUNTER CLOCKWISE. To increase blowdown -MOVE RING DOWN-TURN CLOCKWISE. It is possible to raise the upper ring too far and prohibit attainment of full lift. When this occurs, lower to the point where full lift is attainable and finalize the blowdown setting with the overlap collar (See Overlap Collar Position). If valve fails to lift the lower adjusting ring requires further adjustment. (See LowerAdjusting Ring Position) Check the ring pins to see that the engage the ring grooves, but without touching the bottom The pins should not bear against the rings.
  • 17. 17 4.4 Blowdown Adjustment In arriving at proper blowdown adjustment of the Safety valve it is almost imperative that a lift indicator be used (Fig4). The correct method of obtaining proper blowdown adjustment can be best explained by reference to Fig.5 The upper ring is used to obtain full lift at the popping pressure. However, its position also determines the point at which the valve begins to drop out of full lift and starts the closing portion of its cycle. For example, if the upper ring is in such a position that the valve barely attains full lift at the popping pressure and starts to drop out of full lift at a slight reduction of-boiler pressure, the first portion of the valve cycle will be represented by the line ABF. If it were not for the lift stop, the action of the valve would be represented by the line ABCF.If the upper ring is in a more positive position (lower setting)the action of the valve would be represented by the line ABG and if it were not for the lift stop, the line ABDG.If the upper ring is in a still lower position, the action of the valve is represented by the line ABH and if it were not for the lift stop ABEH. From this it can be seen that a lower position of the upper ring causes that valve to remain in full lift for a long period time and over a greater period of pressure reduction.Refer Figs,6,7 and 8. FIG 4: LIFT INDICATOR ILLUSTRATION Fig 5: lift Diagram as explained in blowdown adjustment.
  • 18. 18 It will further be noted that there is a distinct difference between the actual overlap setting on the valve and the point at which the overlap begins to take effect.This can be understood since the area in the overlap vent begins to reduce considerably ahead of the point where upper corner of the overlap level actually enters the floating washer,Fig 7. This has the effect of rounding off the corner of the diagram at points J,K and L . If the Upper ring is in a position to produce the lineABH the overlap will have to be set considerably higher to obtain a short blowdown than if the upper ring is set at such a position as to produce the line ABF. Excessively high overlap settings are liable to cause seat damage when the valve closes. It is therefore desirable to set the upper ring in such a position as to cause the valve to stay in full lift for as short time as possible most desirous complete cycle is represented by the line ABFJM. CAUTION: When steam safety valves are subjected to an excessively high water level, the valve can be expected to have a long blowdown which the upper ring adjusting ring position will be unable to correct.It is recommended that the cause of high water level be corrected so valves may fuction correctly at the intended conditions. If a superheater valve is set with low temprature steam, it is advisable to for increase the blowdown to compensate the change in the density and other thermal effects taking place when the steam is brought up to working temperature.An approximate rule is to add 0.5 percent of set pressure to the blowdown for each 1000 F(55.60 C)of steam temperature below the final temperature. 4.5 Sealing Valves after Test After testing the valve for proper set point and blowdown , the ring pins,and top lever pin will be sealed for all external adjustments.Seals shall be installed by the manufacturer at the time of inital shipment and after field adjustment or repair of the valves either by the manufacturer,his authorized representative repairer,or the user.Seals shall be installed in such a manner as to prevent changing the adjustment without breaking the seal and,in addition,shall serve as means of identifying the manufacturer ,assembler,repairer,or user making the adjustment.Unauthorized breakage of the seals should be reported to the concerned authorities. FIG 6: VALVE IN FULL LIFT- OVERLAP IN FULL OPEN POSITION FIG7: VALVEININTERMEDIATELIFT- OVERLAP SLIGHTLY ABOVE FLOATING WASHER
  • 19. 19 5. DISASSEMBLY Safety Valve can be easily disassembled for inspection,reconditioning seats,or replacing ternal parts, without altering the spring load and hence the set pressure.Refer to Fig.20 for nomenclature Before starting to disassemble the valve,be sure that the there is no steam pressure in the drum or header then proceed as follows: 5.1 With Retention of spring setting To retain the spring setting of the valve when and only when,a disc is to be replaced or the seating surfaces are to be touched up the following procedures should be followed. Remove the top lever pin and top lever. Loosen cap set screw and lift off cap and drop lever assembly.Remove the cotter pin and turn the Release collar down until it is tight against the top of the spring adjuster,then back off ¼ turn. Install cotter pin in lower hole of spindle. Remove the two top yoke rod nuts and the four cover plate studnuts,and lift the spindle,spring and springwashers,cover plate,disc and disc holder assembly out of the valve .see Fig 9. FIG 9: PARTS REMOVED WHEN RETAINING SETTING 5.2 Disassembly to Component Level Remove theTop Lever Pin and Top Lever. Loosen Cap, set screw and lift off Cap and drop lever assembly. Remove Cotter Pin and release Collar. Remove the two Top Yoke Nuts, the Yoke and Spring adjuster with locknut as an assembly. Then lift the spring and spring washers from the spindle. Unscrew the four cover plate Stud Nuts then lift the Spindle, Cover plate, Disc and Disc Holder out of the valve. Remove the disc by unscrewing it from the coarse right hand thread on the spindle and remove the disc holder. The Guide and adjusting RingAssembly can now be removed from the Base by lifting it straight up. In order that the blowdown of the valve will be unchanged, the position of the Upper Adjusting Ring should be marked for reassembly. Make punch marks in an axial line on a tooth of the Upper Adjusting ring and the outside barrel of the Guide. Then measure over all height of the guide and Upper adjusting ring assembly and record this information. FIG8: VALVE IN CLOSED POSITION OVER- LAPFULLYENGAGED IN FLOATING
  • 20. 20 Measure and record,the height from the valvebushing seat to the recess in the base where the guide would normally rest. This is important so that the amount of metal removed from the seat can be determined. Mark the lower Ring in line with the Lower Ring Pin. Now place a straight edge or a Ring Lap across the top of the seat and count the number of notches that the ring is below the seat. Record this information for reassembly. 6. MAINTENANCE 6.1 General lt. is not necessary to remove flanged or welded valves from the boiler for any maintenance The actual maintenance required is generally confined to touching of seats and occassionally replacing the disc The following are recommended for this i. Flat lapping plate. ii. Grinding compounds iii. High temperature lubricant. Molykote G. iv. Three ring-laps per valve. *Refer Maintenance tools and supplies section also. It may not be necessary to use all of the ring-laps at any one time, but having a sufficient supply on hand will save the time of reconditioning them during a boiler outage. After the boiler is back on the line, the ring-laps should be reconditioned on the net lapping plate or on a special lapping machine. A lap should not be used on more than one valve without being reconditioned. Valves that have been leaking should be disassembled in accordance with prior instructions. Since the position of the adjusting rings has been recorded, the rings can be disassembled for cleaning if necessary. Parts for each valve should be kept together or marked, to make sure that they are replaced in the same valve. Reconditioning of the seat surfaces of the disc and seat bushing is accomplished by lapping with a flat cast iron-ring-lap coated with Grade No.1000 silicon-carbide compound, or equivalent. 6.2 Lapping Procedure The following precautions and hints will enable anyone to do a professional Job of Lapping. seats i. Keep work clean. ii A lap should not used on more than one valve without being reconditioned. iii Apply a very thin layer of compound to the lap.This will prevent rounding off the edges of the seat. FIG.10: RINGOR SEAT LAP
  • 21. 21 iv. Lap, using a figure eight motion in all directions,at the same time applying uniform pressure and rotating the Lap slowly. Care should be used not to run off the seating surface with the lap as this will cause the seat to become uneven. When lapping the disc seat, the Lap should be held stationary and the disc moved as above with care taken not to strike the cone of the disc as this would cause the seat to be high on the inside. vi. To check the seat, remove all compound from the seat and lap. vi. To check the seat,remove all compound from seat and lap.Then using a dry lap and the same lapping motion as above, the low section of the seating surface will show up as shadow in contrast to the shiny portion. If shadows are present, further lapping is necessary. Only laps known to be net should be used, as only a few minutes will be required to remove the shadows. vii. When the lapping is completed, any lines appearing as cross scratches can be removed by rotating the Lap which has been wiped clean from compound on the seat about its own axis. viii. To check ring laps for flatness,wipe all compound off the lapping plate and ring lap. Then use a figure of 8 motion of the ring lap on the lap ping plate. If the lap is flat there will be n o shadow; if there is a shadow coat the lapping plate with compound and lap the ring lap with a figure of 8 motion covering thc lapping plate to remove the shadowFigure 11. ix. The seat now shall be throughly cleaned, using a lint free cloth or tissue paper. If extensive lapping of the bushing seat is required, a great deal of time will be saved if a Roto-Lap is used. See instructions for assembling and operating the rotoLap Machine. Referring to Fig.12 it will be noted that the seat step is 0.635mm (0.025 in.) If this step is reduced to 0.4 mm(0.010in)duetolapping,itshouldberemachinedtotheproperdimensions.Forthispurposethereis availableforusea“ReseatingMachine”whicheliminatestheneedtoremovethevalvefromtheunit.This machine is mounted in place of the coverplate and cuts the top face,inside diameter and outside diametre ofthebushingtoestablishthecorrectheightrelationshipsandangles. FIG12: BUSHING SEAT STEP DIMENSION FIG11: RECONDITIONING OF LAP
  • 22. 22 In re-machining the bushing seat, the length of the disc holder extending above the disc guide will decrease. Referring to the Figure 13 the top of the disc guide should be kept to a distance of atleast 1.587 mm(1/16mm) below the top of the disc holder in case a deposit of dirt forms in the pocket between the two parts. This dimension is obtained by machining the top of the disc guide. 6.3 Checking Spindle Run-out It is important that the spindle be kept very spindle in order to transmit the spring force to the disc without latteral binding. Overgaging and cold gagging is one of common causes of bent spindles.A method to check the essential working surfaces of the spindle disc is illustrated in Figure 14. Clamp a V block (A) made of wood, fibre or other suitable material onto the platform railing .Imbed the ball end of the spindle in a piece of soft wood (B) and place top, of spindle below the threads, in V block (A). Clamp a dial indicator on to the railing and locate at point (C). The total indicator reading should not exceed 0.177 mm (0.007 in.) when the spindle is rotated. Other parts of the spindle not used as working surfaces may run out cosiderably more than0.177mm (0.007 in.) but this should not be regarded as an indication of crookedness or faulty manufacture. To replace the disc, disassemble the valve in accordance with the prior instructions. Then proceed as follows: NOTE: The bushing seat can be reconditioned by hand lapping as explained under ‘Lapping Procedure’. FIG 14: CHECKING SPINDLE CONCENTRICITY. FIG 13: HEIGHT OF HOLDER ABOVE GUIDE
  • 23. 23 The replacement disc has been lapped on a special lapping machine and requires only that the seat be touched up. However, the spindle tip bearing should be re-established by grinding the spindle tip into Ihe disc. This can be done with the removable assembly propped upon the spring adjuster end. Then remove the old disc by unscrewing the coarse right hand thread on the spindle. Remove the disc holder, apply a layer of grinding compound to the ball end of the spindle and screw the new disc on. Grind the bearing using a rotary motion. The spindle nose should be lapped into the disc spindle pocket unil the bearing band is clearly marked. The band position is shown in Figure 15. If the band extends too high on the radius disc may lock up under pressure. If the band is too narrow,the spindle may indent the disc and again the rock will be lost. The table 4 also shows the finished machined size of thespindle nose radius for each orifice size and the flat diametre.If the required bearing band can not be obtained by hand grinding then this radius should be checked and remachined if necessary. When the bearing is re-established,clean both surfaces with kerosene or light oil. Then apply some Molykote to the spherical surface of the spindle tip and work it into the pores by rotating the disc on the spindle. First place this holder on the spindle,allowing it to rest on the face of the disc collar. Then assemble the disc holder and new disc. The disc should be free enough to rock on the spindle tip.If there is no freedom ,lower the collar until the disc is free to rock slightly. Disc collar should then be lowered two notches and secured with stainless steel cotter pin.Disc and disc holder should then be assembled. Clearance between disc and discholder should be 0.381mm (0.015 in) to 0.508mm (0.020 in) see Fig 16. FIG 15 FIG.16: DISCAND DISC HOLDER CLEARANCE
  • 24. 24 7. RE-ASSEMBLY 7.1 Reassembly when spring load Retained After restoring both the bushing seat and the disc seat by using the Lapping procedure. as given in this manual the valve shall be assembled as follows: See Fig. 9 & 20. Apply Molykote G lubricant on all threads. Hold disc holder against disc collar and thread disc onto spindlethreads. Turn disc clockwise until drop out threads in disc pass and disengage from spindle threads. Clean seats thoroughly and lower complete upper assembly into valve body. Install and tighten yoke rod nuts and cover plate nuts till the release collar is free. Backoffreleasecollarandpositionitsothat3.175mm(1/8in.)ofclearenceisvisiblebetweenliftingfork andreleasecollarwhenliftinggearisinstalled. Afterpositioningreleasecollarremoveliftinggearandinstallcotterpin.Installliftinggear. 7.2 Reassembly of valve from component level Settheadjustingringsinthepositionsnotedduringdisassembly.Ifsufficientmetalhasbeenremovedfrom bushing remeasure distance from bushing seat to guide recess in base. Compare this with that measured prior to machining and determine difference. The upper adjusting ring should then be lowered to this additionalamountfromitsoriginalpositioninthevalve. Whenstartingreassemblyifthevalvewhenoriginalringpositionsarenotknownthefollowinginformation is to be used as a guideline. The starting position of the rings can be determined by the following method. i. Lower adjusting ring Place a straight edge on the seat bring the ring up to the straight edge then backing off one notch for each 41.4Bar (600 lbs) of set pressure, Example a valve at 165.6 Bar of set pressure shall be 4 notches below the seat. This applies upto 206.9 Bar(3000 psi) 5 notches downward is considered a maximum lower position. ii. Upper adjusting ring Measure from the top of the guide to the seat,then set the the ring using the measurement as the overall length from the top of the guide to the bottom of the ring.This will place the ring exactly at seat level when guide and ring assembly is placed into valve body. TABLE 4 DISC,SPINDLE CHECK DIMENSION Orifice Nose Radius “R” mm Flat Dia mm Dia ‘d’ mm (inch) 1 7.036+.000-.102 3.175 39.8 (1.567) 2 9.423+.000-.102 4.763 47.8 (1.881) 3 12.573+.000-.127 6.350 63.7 (2.507) 4 12.573+.000-.127 6.350 73.0 (2.874) 5 12.573+.000-.127 6.350 79.6 (3.134) 6 12.573+.000-.127 6.350 106.1 (4.179) 7 17.323+.000-.127 6.350 132.7 (5.224) Q 17.323+.000-.127 6.350 132.7 (5.224) 8 18.110+.000-.127 7.938 150.4 (5.920) R 18.110+.000-.127 7.938 150.8 (6.290)
  • 25. 25 iii. Determining ring position with valve under pressure when valve is under pressure and the position of the rings is not known, their location can be determined by the following method. a. Lower adjusting ring Raise lower ring until contact is established with disc holder.Refer to fig 17 and table 3. Column “A” for number of notches from disc holder to seat . Example : In the case of a 1739 valve (#3 orifice) raise lower ring until it touches disc holder. Referring to Fig 17 and table 3 it will be noted that for a # 3 orifice valve the lower ring must be moved clockwise 12 notches to place ring on a plane with seat. Lower ring can now be positioned by lowering it 1notch for every 41.4 bar (600 psi) of set pressure upto 5 notches maximum.
  • 26. 26 TABLE 3 ADJUSTING RINGS FINAL FACTORY POSITIONS (FIELD STARTING POSITIONS) b. Upper adjusting ring Remove both service port plugs (located on the left side of a valve facing outlet) and with a flash light directed into one service port hole, the upper ring can be raised until the lower face of the ring is on a plane with the disc holder .Referring to Table 3 Column “B” a #3 orifice upper ring will be 16 notches above the seat. Ring should be brought to seat level as a starting point of adjustment When testing the valve refer to “Blowdown Adjustment” for effect of upper ring position. iv. Lift adjustment ln the event that extensive machining has been done on the bushing seat of the valve, it will be necessary to limit the travel of the disc and spindle to the required lift of the valve which is shown in table-1 Refer to Figure 18. The lift of the valve is shown asA. This is the distance from B which is lift stop in the cover plate and C which is the lift stop collar. Before assembling the valve check the dimension from the face of the cover plate to the cover plate lift stop B.Also check the dimension from the top of the valve body to the face lift stop collar C. By adding these two dimensions the lift will be determined. To decrease lift remove the cotter pin D and rotate the lift stop collar counter clockwise. To increase lift, rotate lift stop collar clockwise.(replace cotter pin after each adjustment) Rotating the lift stop collar one notch moves the collar approximately 0.254 mm (0.010 in). One full turn of lift stop collar is l.587 mm (1/6 in.). The lift stopmust be adjusted to the rated lift marked on the name plate plus an additional amount as per table 1. -ifirO ec gnirrewoL otredloH nitaes sehcton )AnmuloC( gnirreppU otredloH nitaes sehcton )BnmuloC( 1 7 01 2 8 21 3 21 61 4 21 61 5 21 61 6 03 54 7 03 54 Q 03 54 8 73 54 R 83 74
  • 27. 27 The additional lift is to compensate for heated condition of the lower spindle when valve is in operation.The following Table indicates bore diameter and-lift: TABLE: 1LIFT SETTING DIMENSIONS To complete the assembly of the valve, place lower spring washer (016) over spindle (046) and lower into position on lower spindle bearing. Place spring (011) over spindle and gently lower until firmly seated on lower washer (016). Place upper spring washer (012) over spindle and seat into spring making sure arm of upper washer engages yoke rod (009). Place yoke and spring adjuster with locknut as an assembly (008,101,102) over spindle (006) and both yoke rods (009) and lower until Spring adjuster (101) contact upperwasher (012). Install two yoke nuts (231) and pulldown evenly until made up tightly on yoke (008), with yoke in full contact with yoke rod shoulders. Install release collar ( 131 ) on top of spindle (016)and thread clockwise until release collar is fully engaged on spindle thread. Install cap (126) with drop Iever (127) over release collar (131) and seat firmly into place on yoke (008). Install top lever (128) in cap (126) and insert pin (130) through top lever and cap holes. Adjust release,collar downward until it clears top lever by 1.587 mm (1/16 in.) to 3.175 mm (1/8 in). Remove Iever pin (130)) top lever (128) with cap (126). Insert cotter pin (185) through release collar slots ad spindle and spread cotter pin ends. Reassemble cap (126) with drop lever(127),top lever (128),top lever pin (130) and then install cotter pin to lock top lever pin in place. v. Overlap adjustment The overlap collar is a secondary adjustment point for blowdown control. It is utilized in conjuction with upper adjusting ring , in no case should the overlap collar be used exclusively for blowdown setting without first giving due adjustment attention to the upper adjusting ring. The overlap collar is moved downward to shorten blowdown and upward to lenghten blowdown. Orifice Bore Diameter Mm(in.) Rated lift Mm (in.) Additional lift Recommended Mm(in.) 1 28.6(1.125) 7.16(0.282) 0.254(0.010) 2 34.3(1.350) 8.59(0.338) 0.508(0.020) 3 45.7(1.800) 11.43(0.450) 0.762(0.030) 4 57.2(2.250) 14.30(0.563) 1.270(0.050) 5 52.4(2.062) 13.13(0.517) 1.016(0.040) 6 76.2(3.000) 19.05(0.750) 1.524(0.060) 7,6”-Q 95.3(3.750) 23.83(0.938) 1.778(0.070) 4”-Q 100.3(3.948) 25.02(0.985) 1.778(0.070) 8 108.0(4.250) 27.00(1.063) 2.032(0.080) R 114.7(4.515) 28.68(1.129) 2.286(0.090)
  • 29. 29 After final setting , be sure to lock the overlap collar in position by installing the cotter pin, and sealing wire. The overlap collar is marked with four scribe lines placed in such a position that when the lower scribe line is even, or on the same plane with the top floating washer, the angle on the lower end of the overlap collar is on the same plane with the lower floating washer. See Fig.19 From this position, the overlap is to be set according to Table 2. (This is a starting position only). As reference each notch advances the overlap 0.254 mm (0.010 in.) and each scribe line is one complete turn of the overlap collar or 1.587 mm (1/16 in.) As a starting position of the overlap use Table-2 for bore diameter and overlap dimension. After setting overlap, lock overlap collar (054) in place with cotter pin (184). On some smaller valves it may be required that a mirror be used for locating the overlap scribe lines.Should this prove not possible, disassembly of thre top works and spring washers will be required. An approximate guide to further adjustment positioning of the overlap collar in making final blowdown adjustrment would be as follows: Orifice Movement of Overlap Collar 1,2 & 3 May not need further adjustment. If needed , move I notechat at time. 4 & 5 First adjustment 5 notches subsequent adjustments 2-3 notches each time. 6 First and Subsequent adjustment ,5 notches each time. 7,Q,8&R First and subsequent adjustment, 50-60 notches each time. THE OVERLAPCOLLAR POSITIONS SHOWNARE FINALFACTORYSETTINGS BUTONLY STARTING POSITIONS FOR FIELD SETTING OF BLOWDOWN, FURTHERADJUSTMENTS MAY BE NECESSARY. TABLE 2 OVERLAP SETTING DIMENSION o rific e B o re d ia m e te r M m (in .) O v e rla p M m (in .) 1 2 8 .6 (1 .1 2 5 ) 1 .5 2 4 (0 .0 6 0 ) 2 3 4 .3 (1 .3 5 0 ) 1 .7 7 8 (0 .0 7 0 ) 3 4 5 .7 (1 .8 0 0 ) 2 .0 3 2 (0 .0 8 0 ) 4 5 7 .2 (2 .2 5 0 ) 2 .5 4 0 (0 .1 0 0 ) 5 5 2 .4 (2 .0 6 2 ) 2 .2 8 6 (0 .0 9 0 ) 6 7 6 .2 (3 .0 0 0 ) 3 .3 0 2 (0 .1 3 0 ) 7 ,6 ”-Q 9 5 .3 (3 .7 5 0 ) 4 .0 6 4 (0 .1 6 0 ) 4 ”-Q 1 0 0 .3 (3 .9 4 8 ) 4 .0 6 4 (0 .1 6 0 ) 8 1 0 8 .0 (4 .2 5 0 ) 4 .5 7 2 (0 .1 8 0 ) R 1 1 4 .7 (4 .5 1 5 ) 5 .0 8 0 (0 .2 0 0 )
  • 30. 30 8. HYDROSTATIC TESTING AND GAGGING 8.1 During any hydrostatic test all safety valves on the unit must be gagged. This gagging procedure prevents the possibility of damage of the safety valve internals in the event that the test procedure exceeds the safety valve set pressure. When valves are subjected to working hydrostatic tests not exceeding the set pressure of the low set valve, valves may be gagged rather than using hydrostatic test plugs. For higher pressures hydrostatic plugs should be used and valves should be gagged. ProbablythemostcommonsourceofSafetyValvetroubleisovergagging.During Hydrostatic Testing and Safety Valve Setting Gags should be applied only hand tight. During setting,over gagging will also cause damage to the seating surface and the resultant Ieakage. In applying gags remember that the valve spring will hold the valve closed against its set pressure. The additional gag load applied should be only enough to insure that the valves do not lift at the expected over- pressure. Gags should never be applied when the boiler is cold. The spindle of the safety valve expands considerably with the temperature increase as pressure is raised. If it is not free to expand with this temperature change it may become seriously bent. Boiler pressure should be brought up to within 80% of the pressure of the low set valve before applying thegags. Tightenthegagsofdrumandsuperheatervalveswithonlyalightforceappliedtothegagstem. Reheater valvesrequireagreaterforceappliedtothegagstemtoholdthevalveclosedduringhydrostatic test. Application of Test Gags (All Pressures) i. Refer to Fig. 20. Remove top lever pin (130), top lever (128) then loosen cap screw (238) remove cap (126) and Drop lever (127) as an assembly. The release collar (131) is fixed to spindle (046) by means of a cotter pin(185). Note that the release collar(131) does notquite engage top of spring adjuster (101). See fig for details or release collar position. ii. Center the test gag stem on the exposed end of the spindle (046) and hook the legs of gag under the sides of the yoke as shown in Fig.23 DO NOTAPPLY THE GAG LAOD UNTILTHE BOILER HYDROSTATIC PRESSURE IS EQUALTO 80%OFTHE PRESSURETO WHICH THE LOWSETVALVE ISADJUSTED. iii. Apply the gag load by turning the gag stem clockwise. Any attempt to pinch off the leakage through the valve without first lowering the hydrostatic pressure is liable to result in damage to the valve seats. If the gag on the valve has not been tightened sufficiently, the valve will leak and sometimes the leakage is accompanied by “Sizzling” sound. If this occurs the hydrostatic test pressure should be reduced until the valve becomes tight and then gag should be tightened further. This procedure must be followed exactly since it is very difficult to stop the leak by additional gagging once it has started. iv. After the hydrostatic test is completed,the gags should be removed when the hydrostatic pressure has been reduced to 85% to 90% of the pressure of the low set valve.
  • 31. 31 UNDER NO CIRCUMSTANCE SHOULD THE GAGS BE LEFT ON VALVES WITH NO HYDROSTATIC PRESSURE ON THE SYSTEM NEVER TRY TO ARREST LEAKAGE BY FURTHER TIGHTENING THE GAG. Nomenclature List: Fig. 20 002 Base 003 Seat Bushing 004 Inlet Neck 008 Yoke 009 Yoke rod 011 spring 012 Upper Spring Washer 016 Lower Spring Washer 026 Disc 028 Disc Holder 029 Disc Collar 031 Guide 036 Upper Adj.Ring 037 Upper Ring Pin 038 Lower Adj.Pin FIG 20(A) FIG 20
  • 32. 32 039 Lower Ring Pin 046 Spindle 052 Lift Stop 054 Overlap Collar 056 Cover plate 057 Lower Washer Retainer 058 Lower Floating Washer 059 Lower washer Retaining Pin 061 Top Plate 062 Upper Washer retainer 063 Upper Floating Washer 064 Upper Washer Retaining Pin 101 Spring Adjuster 102 spring Adjuster Lock Nut 105 Service Port Plug 126 Cap 127 Drop Lever 128 Top Lever 129 Drop Lever Pin 130 Top Lever Pin 131 Release Collar 182 Disc Collar Cotter Pin 183 Lift Stop Cotter Pin 184 Overlap Collar Cotter Pin 185 Release Collar Cotter Pin 226 cover plate stud 229 cover plate nut 231 Yoke Rod Nuts 232 Lower Yoke Rod Nuts 237 Retainer screw (Top Plate) 238 Cap Set Screw 8.2 Hydrostatic test plug removal FLANGED INLET SAFETY VALVES SHOULD BE REMOVED FROM THE BOILIER DURING THE HYDROSTATIC TESTS AND BOILER NOZZLES BLANKED OFF. Welded inlet valves are fitted with hydrostatic test plugs. These valves are identified by a White Caution tag with red Ietters attached to the internal plug by wires extending through the drain hole in the valve body See Fig.21.
  • 33. 33 8.2 Hydrostatic test plug removal FLANGED INLET SAFETY VALVES SHOULD BE REMOVED FROM THE BOILIER DURING THE HYDROSTATIC TESTS AND BOILER NOZZLES BLANKED OFF. Welded inlet valves are fitted with hydrostatic test plugs. These valves are identified by a White Caution tag with red Ietters attached to the internal plug by wires extending through the drain hole in the valve body See Fig.21. The hydrostatic plugs are placed in the bore of the valve, inside the sealing surface. Their purpose is two-fold. First they effect closure at a point differing from the seating surface of the valve so that if the valve is lifted on hydrostatic test, the seating surface will not be as liable to become damaged. Second, by raising the spindle of the valve and increasing spring compression, the set pressure of the valve is increased to a point where the valve will not leak at one and one-half times design boiler pressure. It is not necessary to gag safety valves tightly when hydrostatic plugs are used. These plugs must, of course, be removed from the valves prior to placing the boiler in service. However, they should be stored carefully and reinstalled whenever a hydrostatic test exceeding the low set valve pressure is conducted. Hydrostatic plugs can be Ieft in the valve until steam blowing is over. When hydrostatic plugs are installed in the Valves, the disc is removed and clipped in preservative, then packed in a box. The package is then inserted into the valve outlet and taped to the floor of the valve body. FIG.21: CAUTION TAG FIG.22: HYDROSTATIC TEST PLUGINASSY
  • 34. 34 iv. Then lift the spindle, springs, spring washers, cover plate ,disc and disc holder as an assembly out of the valve. v. Remove ‘seal peel’ preservative from disc thoroughly clean disc seat with a clean cloth. vi. Lubricate spindle tip with “Molykote G” and assemble disc and disc holder to spindle by turning disc clockwise until dropout thread disengages. vii. Place complete upper assembly in valve body viii. Install and tighten Yoke Rod Nuts and Cover plate nuts. ix. Remove cotter pin from release collar and position release collar so that 3.175 mm(1/8in.) of clearance is visible between Lifting fork and release collar then install cotter pin through the spindle at the upper hole. x. Install lifting gear. FIG3: APPLICATION OF TEST TAG 9. FIELD SERVICE AND REPAIR 9.1 Factory Setting Vs. Field Setting Every Safely Valve is set and adjusted on steam before shipment from the factory. Blowdown adjustments are made is carefully and accurately as possible on the factory test boiler. However it must be recognized that actual field operating conditions may vary considerably from factory test conditions. Conditions beyond the manufacture’s control that affect safety valve operation are: i. Quantity of steam being discharged through the valve, i.e. the actual installation capacity exceeding that of the test boiler, thus permitting the valve to flow its full rated capacity. ii. Quality of steam being discharged. iii. Discharge piping stresses and back pressure. iv. Ambient temperature. v. Shipping or storage damage. vi. Improper gagging. vii. Improper bolting of flanges viii. Damage due to foreign material in the steam. xi. Damage, during disassembly and assembly in the field
  • 35. 35 Final Safety Valve adjustments made on the actual installation is the best means of ensuring that the valves perform in compliance with the applicable code requirements. 9.2 Recommended Spare parts for 1700 Safety Valves TABLE 5 Class I & II parts are most frequently replaced due to wear and tear in normal service. Parts covered in Class III and IV are seldom replaced and may be stocked, based on customers experience or requirements. Refer to Fig. 20 for part name. All others required information will be found stamped on the name plate attached to the body of the valve. In addition, the serial number is stamped on the top edge of the outlet flange. Be sure to include the one or two letters preceding the figures in the serial number ssalc emaNtraP relioBlacitirC-buS )raB7.022-isp0023rednU( noitceStaeheRretaehrepuSmurD deeN ytilbaborP.pmeTdna.rPteSepyT/emaS/trap/ytQ egarevocfossalCezis ecivreSnievlav I csiD.1 4/11/11/1 gniR.jdA.2 )reppU(niP %074/11/11/1 niPgniR.jdA.3 )rewoL( 4/11/11/1 gniR.jdA.4 )reppU(niP 4/14/14/1 niPgniR.jdA.5 )rewoL( 4/14/14/1 II redloH.6 %584/14/14/1 eldnipS.7 6/12/12/1 ediuG.8 4/14/14/1 ralloCpalrevO.9 6/14/14/1 ralloccsiD.01 6/14/14/1 potStfiL.11 6/14/14/1 III gnirpS.21 6/16/16/1 gnirpS.31 )2(rehsaW %596/tes/16/tes/16/tes/1 noisserpmoC.41 wercS 6/14/14/1 palrevO.51 niPralloc 6/14/14/1 ralloCcsiD.61 niP 6/14/14/1 niPpotStfiL.71 %996/14/14/1 noisserpmoC.81 tuNwercS 6/14/14/1 etalPpoT.91 swercS 4/tes14/tes14/tes1
  • 36. 36 The table 5 gives the recommended spares quantity required based on valve location. Spares may be ordered by giving: 1. Part Name 2. Quantity along with the valve details. 3. Size 4. Type 5. Temp. Class 6. Serial No. Eg.3" 1759 WB: Sl.No. Disc-2 Nos. 9.3 Maintenance TOOLs and Supplies LAPPING TOOLS: Thc following tools are required for proper maintenance of Safety Valve seats: Ring Lap-The ring lap is used for lapping the nozzle and disc seats. Lapping Plate-The lapping plate is used for reconditioning the ring laps. Only one 275mm (11”) diameter plate is required for all sizes of ring laps. Lapping Compound -Lapping compound is used as a cutting medium for lapping and polishing the seats and bearing surfaces in Safety Valves. i. *RING LAPS (See Note 1). **Valve Orifice Lap Tool No. (See Note 2) Part No. 1 1672806 44.54151.00 2 1672807 44:54152.00 3 1672808 44.54153.00 4 1672810 44.54155.00 5 1672809 44.54154.00 6 1672811 44.54156.00 7 & Q 1672812 44.54157.00 8 & R 1672814 44.54159.00 NOTE 1: One set of (3) Ring Laps is recommended for each orifice valve in service to assure ample flat laps are available at all times. NOTE 2: Valve Orifice number is third digit of the valve type number,eg a 1737WA valve has a orifice no. of 3. ii. Resurfacing Plate 275mm( 11 “) Diametre
  • 37. 37 iii. Lapping Compounds Grift Lapping Function 320 General 500 Finishing 1000 Polishing iv Lubricant Location Lubricant Bearing Points a. Spindle/Disc b. Spring adjuster top Spring Washer Molykote “G” c. Spindle/Bottom All Threads Molykote “G” All Nut Contacts Faces Molykote “G” v. Roto-Lap Machines vi. Reseating Machine 10. GUIDELINES FOR THE STEAM TESTING OF BOILER SAFETY VALVES Please take five minutes to read this short guideline. Implementing the following procedures will benefit your company in good valve performance, reduced labor time and fuel savings. Mechanical 1. We highly recommend a preliminary test at reduced pressures of the boiler valves with our 1566 hydroset prior to steam. Savings in fuel and time will easily justify this step. 2. Only calibrated test gauges should be used for testing safety valves. Gauges not calibrated can cause problems with operating pressure later or even necessitate the retesting of all the safety valves. 3. Gage for each valve should be available and in good condition. 4. Discharge piping has to be inspected for binding on the valves,supports and welds on piping. Binding of the discharge could make the valve hang up on closing. Insufficient welds and supports could cause the dicharge piping to fly off during valve activation. 5. A rope approximately 5 to 7 metres with a hook one end should be attached to the valve lifting lever before activation.Should the valve chatter or not lift at set pressures, the rope can pulled, Eliminating chatter and stop over pressure of the vessel. 6. Have the correct tooling available. Looking for tools means lost lime. Having incorrect tools can cause damage to compression screws and other valve parts. 7. Establish a good communication system between the boiler and control room.
  • 38. 38 This eliminates mistakes that could be dangerous and time consuming. Operational 1. If the unit has an electric pilot operated relief valve “Electromatic”, place this valve in operation first. Since safety valves are tested one at a time and the other valves are gagged, the pilot actuated relief valve will increase the safety factor of the unit while testing. Pilot operated valves can be actuated from the control room if some emergency should develop during the controlled burner firing associated when tests are being conducted. The electromatic will help clean contamination from system. 2. The Drum valve should be tested first Possiblities of valve part damage because of “girl blasting” are greater on superheated valves in contrast to the drum valves. If a super heated valve is gagged after seat damage while testing of other valves continues, the total valve damage will most likely be increased. Tempratures of the boiler increase during the testing cycle of the Drum Valves. Consequently higher temperature steam will be available for testing the Superheater valves and produce more accurate results. Keep water level down as low as possible while testing drum valves. If drum valves level is high the SafetyValve may be stugged with water causing a long blowdown and possibly damage the valves 4. Pressure should be brought up evely and fairly rapid rate A slow raise in pressure will increase the simmer of the valve possibly causing the valve to life erractically. We recommended 2 to 3 kg/cm2 per minute increase in pressure during testing to be optimum. Should a burner or other systems fail when pressure is near the set pressure of the valve, drop boiler pressure al Ieast 10 percent below set pressure before raising boiler pressure again. Holding boiler pressure near the set pressure of the valve will induce simmer, possibly causing the valve to lift erratically. 6. Drop pressure after a valve has lifted to a safe level before taking the gag off the next valve or making-valve adjustments. 20 percent of the valve set pressure will assure the nongagged valve will not lift prematurely. 7. If a valve has to be lifted several times, a cooling off period will be necessary. For outside or inside valve installalion, 25-30 minutes is sufficient: If this cooling period is not maintained, erratic operation of the valves can be expected. 8. If the valves have not been tested with the hydroset prior to the steam actuation, it is recommended to hand lift the valves before the actual steam pop. Hand lifting the valves will show that the valves are functional Furthermore, it will help to warm up the valves.
  • 39. 39 Safety For the protection of persons in testing be valves, a few simple steps can, prevent accidents and injury. 1. Have only people on the boiler absolutely necessary for the testing of the valves. 2. Rope off the area where valves are going to be tested. 3. When working on the valves, wear glooves 4. All personnel on the boiler are to wear eye and ear protection. 5. Warn people on the plant site that valve testing is being performed. The recommendations we have made represent many years of field experience. We hope you can implement some or all of them. Hopefully, you will have a good start up. INDEX