Safety Valves

1. Safety Valves

2. • Describe the different types of Safety valves.
• Describe the parts and operation of a typical
huddling safety valve.
• Describe the method for making safety valve
adjustments.
• Describe ASME code requirements as they
relate to Safety Valves.
• Describe testing procedures for safety valves.
Objectives

3. Safety Valve Setting
• Safety valve or Relief valve capacity shall be
such that they will discharge all the steam
generated by the boiler without allowing the
pressure to rise more than 6% above the
highest pressure at which any valve is set
and in no case more than 6% above the
maximum allowable working pressure.

4. Safety Valve Setting
• One or more safety valves on the boiler proper
shall be set at or below the maximum
allowable working pressure.
• If additional valves are used the highest setting
shall not exceed the maximum allowable
working pressure by more than 3%.

5. Safety Valve Setting
• The complete range of pressure settings of all
the saturated steam safety valves shall not
exceed 10% of the highest pressure to which
any valve is set.
• Pressure setting of Safety Relief Valves on high
temperature water boilers may exceed this
range.

6. • Code
– Each boiler shall have at least 1 safety valve.
– Above 500 square feet, 2 or more safety valves are
required.

7. • Twin Valves:
– Valves will be the same size when attached on a
common (Y Base).
– When separately installed, they may be different
sizes. The smaller valve will have a capacity of 50%
of the larger one.
• Spring Limit:
– Up to 250 PSI 10%
– Above 250 PSI 5%

8. • Safety Valve:
– An automatic pressure-relieving device actuated by
the static pressure upstream of the valve and
characterized by full opening pop action.
– It is used for gas or vapor service.

9. • Relief Valve:
– An automatic pressure-relieving device actuated by
the static pressure upstream of the valve, which
opens further with the increase in pressure over the
opening pressure.
– It is used primarily for liquid service.
– Has no huddling chamber.
– A safety valve may be used as a relief valve.

10. • Safety Relief Valve:
– An automatic pressure actuated relieving device
suitable for use either as a safety valve or relief valve,
depending on application.
– Frequently used on the auxiliary systems such as
heaters, condensate returns boiler feed pump
turbines, evaporators, economizers, compressors,
pumps, etc.
– Safety relief and Relief valve testing frequency can be
as short as 6 months or as long as 2 years.

12. • Lifting:
– The kinetic energy produced in the huddling chamber
causes the safety valve to open.
– The name plate capacity lift (in inches) is a
measurement of the spindle travel or "lift". The spindle
should travel a distance equal to or greater than the
nameplate identified "lift" value.

13. • Lifting
– The initial lift is produced when the steam pressure
under the disc exceeds the spring pressure. To assist
in starting the popping, the small jet of steam that
escapes at low lift is deflected by a small angle on the
nozzle ring. The escaping steam begins to react
against the upper guide (adjusting ring) and push the
disc up to a high lift.

14. • Lifting
– The reaction of the deflected steam pushes against
the under side of the disc and lifts it still higher on an
accumulation of pressure. In this way the valve
reaches a lift equal to or greater than "full bore" lift
within an accumulation of 3 percent above the set
pressure.
– Lifting arm can swivel through a 225 degree arc on
the valve body.

15. • Lifting Pressure:
– Determined by spring tension.

16. • Blowback (Blowdown):
– Determined by escape area between adjusting ring
and nozzle ring.
– Adjustments of over 10 notches on rings requires re-
testing of safety valve.
– The difference between opening and closing
pressures.

17. • Blowback (Blowdown):
– 4% but not less than 2 PSI, except on:
1.Boilers of Once Through or Forced Circulation with no fixed
water level; Blowback will be 10%.
2.Safety valves open and remain open below set pressure

18. • Adjusting Ring:
– Moving towards safety valve seat (Left) increases
blowback.
– Used for major adjustments, controls the amount of
blowdown/blowback.
– DO NOT move more than 10 notches without
retesting. Always record number of notches valve
was adjusted.

19. • Nozzle Ring:
– Moving towards safety valve seat (( Right) increases
blowback.
– Used for minor adjustments, such as when warn (also
called simmer) must be eliminated.
–
– DO NOT move more than 1 notch without
retesting. Always record number of notches valve
was adjusted.
– On high-pressure valves the nozzle ring can be very
effective in reducing the blow down

20. • Discharge Line:
– At least 1 pipe size larger than valve outlet.
– Direct as possible to atmosphere.
– Adequately supported for expansion.
– Open blow drain at base.

21. • Valve Drain:
– Adequate drain below seat level.
• Full Bore Opening:
– Maximum effective lift will be equal to diameter of disk
divided by 4. ( D / 4).
– Full Bore" is that point where the area of the nozzle,
rather than the lift, limits the discharge capacity of the
valve.

22. • Set Pressure
– Maximum allowable pressure

23. • Blowback Adjustment
– Major Adjustments, Adjusting Ring.
– Fine Tuning, Nozzle Ring.
– If you are adjusting the ring and you move it 10
notches to get proper adjustment, then the safety
valve requires an overhaul.
– Both rings have right-handed threads.

24. • Blowback Adjustment
– Moving rings to the right (or anti-clockwise)
RAISES rings.
– Moving rings to the left (or clockwise) LOWERS
rings.
– To increase blowback move rings CLOSER
together.
– To decrease blowback move rings APART from
each other.
– Gag safety valve while adjusting.

25. • Opening Pressure or Popping Pressure
– When the popping pressure is changed, a slight
adjustment of the blow down may be required.
– Raising the popping pressure lengthens the blow
down, lowering the popping pressure shortens it.
– A change of less than 5 pounds usually does not
call for any adjustment

26. • Over-pressure Situation
– When the safety valve fails to open, reduce
pressure, try lifting by hand, then raise
pressure to popping point.
– If the safety valve will not open, DO NOT try
to lift the valve manually while at popping
pressure. Take the boiler down and overhaul
the valve.

27. • Over-pressure Situation
– If the valve does not operate at its set
pressure and does not respond to
readjustment, do not attempt to free it by
striking the body or other parts of the valve.
That valve should be repaired while the boiler
is out of service.
– Do not attempt to stop valve leakage by
compressing the spring or using excessive
gagging force.

28. • Safety Valve Failures:
– The most common cause of safety valve
failing to open at the set pressure is the
accumulation of corrosion deposits between
the valve disk and seat.
– This usually happens when the safety valve
"weeps" or leaks slightly

29. • Manual Operation:
– At 75% of boiler pressure a safety valve can
be manually lifted.
• Material:
– The disc and seat are made of a non-
corrosive material.
– Carbon steel will not be used because carbon
makes the steel corrode.

30. • Discs:
– Seat and discs may be either flat or 45o.
– Seat can be inclined at any angle between
45o and 90o inclusive, to the centerline of the
spindle.

31. • Saturated Valves:
– Highest set valves 3% above maximum
allowable pressure.
– Range 10% from lowest to highest set valve.
– If one valve is set at or below maximum
allowable pressure then under no condition
will pressure exceed maximum allowable
pressure by more than 6%.

32. • Superheater Valves:
– Integral superheater safety valve is set
approximately 5% below lowest saturated
valve.
– Capacity of superheater safety valves equals
25% of total capacity of boiler.
• Reheater Safety Valves:
– They are NOT INCLUDED in the relieving
capacity of the boiler

33. • Enclosed Spring Safety Valves:
– The maximum temperature limit is 450oF.
– A cooling spool is used to dissipate heat from
the spring.

34. • Relieving Capacity:
– Can be determined by three different
methods.
– Accumulation Test.
– By calculation using the evaporative capacity
of a boiler.
– And by the fuel burning capacity of a boiler.

35. • The minimum required relieving capacity
of the safety valves or safety relief valves
shall not be less than the maximum
designed steaming capacity as determined
by the manufacture.
• An economizer, which may be shut off
from the boiler to become a fired pressure
vessel, shall have one or more safety
valves.

36. • Accumulation Test:
– Can not be done with an attached
superheater or reheater.
– If superheater is separately fired and a stop
valve is located between the boiler drum and
superheater then the accumulation test can
be done.

37. • Accumulation Test:
– An accumulation test is done with all steam
outlets closed and fires at maximum. When all
safety valves have lifted, the pressure will not
exceed maximum allowable by more the 6%.
– Use a test gage when doing accumulation
test.
– Over 6% you need more safety valves or
increased relieving capacity of existing safety
valves.

38. • Water Level:
– When testing safety valves with steam, the
drum level should be normal.
– Feed only sufficient water to maintain the
level.
– The temperature in the drum can also effect
the valve operation.

39. • Police Pop Valve:
– It is used in heating systems.
– It is a pressure-relieving valve.

40. • Foaming, Priming, Carry over, Oil:
– When condition has been rectified, lift the
safety valve by hand.
• Hydrostatic Test:
– Remove safety valves and blank off flanged
connections rather than installing gags.

41. • Gags:
– Finger Tight only.
– Adjusted at 80% of hydrostatic test pressure.

42. ASME Code Excerpts regarding Safety Valves
Code 67-1: Each boiler shall have at least one safety valve or safety relief valve. If it has more
than 500 square feet of bare tube water heating surface, it shall have at least two valves.
For a boiler with a combined bare tube and extended water heating surface exceeding 500
square feet, two or more valve are required only if the designed steam generated capacity
of the boiler exceeds 4,000 lbs./hr.
Safety Valve: An automatic pressure-relieving device actuated by static pressure up stream of
the valve and characterized by full bore pop action. It is used for compressive fluid service
(gases).
Safety Relief Valve: An automatic pressure actuated relieving device suitable for use either as a
safety valve or a relief valve depending on application.
Relief Valve: An automatic pressure-relieving device actuated by static pressure upstream of
the valve and keeps opening further as pressure increases (no pop action). It is used
primarily for non-compressible fluid service (liquids).
Code 67-2: The safety valve capacity for each boiler shall be such that the safety valve or
valves will discharge all the steam that can be generated by the boiler without allowing the
pressure to rise more than 6% above the highest pressure at which any valve is set and in
no case more than 6% above the maximum allowable pressure.
Code 67-2.1 : The minimum required relieving capacity of the safety valves on any boiler shall
not be less than the maximum steaming capacity determined by the manufacturer.

43. Code 67-3: One or more safety valves on the boiler proper will be set at or below the maximum
allowable pressure. If additional valves are used, the highest set pressure shall not exceed
maximum allowable pressure by more than 3%. The range of all safety valves on the boiler shall
not exceed 10% of the highest pressure to which any valve is set.
Code 67-4: On a universal boiler with no fixed water level equipped with automatic controls and
protective interlocks responsive to steam pressure, safety valves may be provided as above, or
the following overpressure protection shall be provided.
One or more power actuated pressure relief shall be provided in direct communication with the boiler
when the boiler is under pressure and shall receive a control signal to open when the maximum
allowable pressure at the superheater outlet is exceeded.
The combined relieving capacity of all such valves shall not be less than 10% of the maximum
designed steaming capacity under any load condition.
Code 67-:4.1 An O.S.&Y isolating valve may be installed between the relief valve and the pressure
source to allow maintenance.
Power actuated pressure relief valves discharging to intermediate pressure stages or incorporated into
bypass and/or startup circuits need not be capacity certified.
Code 67-4.1: Power actuated pressure relief valves that discharge directly to the atmosphere will be
capacity certified.
Spring loaded safety valves shall be provided having a combined total relieving capacity, including that
of the power actuated pressure relieving capacity of not less than 100% of the designed steaming
capacity of the boiler. In this total, no credit in excess of 30% of the total required relieving
capacity shall be allowed for the power actuated pressure-relieving valves.
Code 67-4.2: The set pressure of the safety valves shall be such, that when they (together with the
power actuated relief valves) are in operation the pressure will not rise more than 20% above the
maximum allowable pressure of any part of the boiler.
All safety valves shall be so constructed that the failure of any part cannot obstruct the free and full
discharge of steam from the valve. Safety valves shall be direct spring loaded with seats inclined
at any angle between 45 degree and 90 degree inclusive to the centerline of the spindle.

44. Code 67-5: Deadweight or weighted lever type safety valves shall not be used.
Code 67-7: Safety valve may have bronze parts provided temperature and pressure limitations are not
exceeded. They shall not be used on superheaters delivering steam at a temperature above
450°F and 306°F respectively.
Every attached superheater shall have one or more safety valves located between the superheat
outlet and the first stop valve. The exact location of each valve shall be such that uniform steam
flow through the superheater is maintained regardless.
Code 68-1: The pressure upstream of each valve shall be considered in the determination of set
pressure and relieving capacity.
Code 68-2: When there are no intervening valves between the boiler and the superheater, the
discharge capacity of the superheat safety valves will be included in the total relieving capacity of
the boiler provided the discharge capacity of the boiler safety valves is at least 75% of the total
required.
Code 67-4: Every reheater will be protected from overpressure by one or more safety valves but they
are not included in the required relieving capacity for the boiler and superheater.
Code 68-5: A soot blower connection may be attached to the same outlet from the superheater or
reheater that is used for the safety valve connection.
Every safety valve discharging superheated steam above 450 degrees F shall have a casing, including
the body, base, spindle, and bonnet of steel, steel alloy or equivalent heat resisting material. The
seat and disk shall be of heat erosive and corrosive material.
Code 68-6: The spring fully exposed will be protected from direct contact with escaping steam by a
cooling spool and deflector.
Capacity certificate tests shall be conducted at a pressure, which does not exceed the set pressure by
3% or 2 psi, whichever is greatest.
Safety valves will be adjusted so that the blowdown does not exceed 4% of the set pressure for valves
set below 100 psi, the blowdown shall not exceed 4 psi.

45. Code 69-1.4: On universal boilers with no fixed water level, safety valve blowdown will not exceed
10% of the set pressure.
Code P 67-1: When two safety valves are independently installed on a boiler, the smaller valve will
have a relieving capacity not less than 50% of the larger valve. Multiple valves installed on a
common "Y" base or common body will be of equal size and capacity.
Safety valves shall be installed independent of any other connection and as close as possible to the
boiler or pressure source, without any unnecessary intervening pipe or fitting. Any such
intervening fitting cannot be longer than the face-to-face dimension of the original fitting.
Every safety valve will be installed so that the spindle is vertical.
The opening or connection between the boiler and the safety valve shall be equal to at least the area
of the valve inlet.
No valve of any description shall be placed between the boiler and the safety valve or, the safety valve
and the atmosphere. The cross sectional area of the waste pipe shall be not less than the area of
the valve outlet or of the total of the areas of the valves discharging thereto.
It shall be as straight and direct as possible to the atmosphere and properly supported to avoid undue
stress on the valve or valves.
Provision for gravity drain shall be made in the waste pipe at or near each valve.
If a muffler is used on a safety valve, it shall have sufficient outlet area to prevent backpressure
interfering with the proper operation of the valve. The muffler plate will be arranged so as to
prevent restriction of steam flow due to deposits.

46. Code 71-4: Safety valves exposed to outdoor elements that could affect operation may be shielded by
a cover properly installed to permit servicing and normal operation.
Safety valves are designed and constructed to operate without chattering and attain full bore opening
at a pressure no greater than 3% above their set pressure. After blowing down all valves will close
at a pressure not less than 96% of the set pressure of the lowest set drum value.
The minimum blowdown shall be 2% of the set pressure except when the maximum allowable
pressure is less than 100 psi, in which case blowdown will be between 2 and 4 psi.
Code 72-1: Safety valves for universal boilers with no fixed water level shall be adjusted for a
blowdown not more than 10% of the set pressure and marked accordingly.
Code 72-3: The spring in a safety valve shall not be reset for any pressure more than 5% above or
below that for which the valve is marked.
Popping point tolerance plus or minus shall not exceed:
Pressure Tolerance Range
Up to 70 psi 2 psi
70 to 300 psi 3%
300 to 1,000 psi 100 psi
Above 1,000 psi 1%
To verify that a safety valve is free to lift, a substantial lifting device shall be installed which allows
manual lifting of the valve when boiler pressure reaches 75% of the set pressure

47. Code 73-1.3: The lifting device shall be such that it cannot hold the disk in the lifted position when the
external force is removed.
Means shall be provided so that all external adjustments can be properly sealed by the manufacturer
or his authorized agent or assembler.
Code 73-1.4: The seat of a safety valve shall be attached to the body of the valve so that there is no
possibility of the seat rising.
A body drain below seat level shall be minimum 3/8" n.p.s. when the valve exceeds 2 1/2" n.p.s. below
2 1/2" n.p.s. The drain shall be minimum 1/4" diameter.
Code 73-2.1: Cast iron seats and disks are not allowed.
Code 73-2.2: Adjacent sliding surfaces such as guides and disks or guide holders shall be corrosion
resistant material.
Safety valves must be gagged or have hydrostatic test plugs installed prior to hydrostatically testing
the boiler.
Test plugs are recommended especially for pressures above 2,000 psi where misapplication of gags
could result in safety valve seat or spindle damage.
Code 2.272: Gags will not be fully tightened until hydrostatic pressure is 80% of operating pressure.
Code 4.110: Inspection and testing of safety valves should be performed on an annual cycle.

48. GENERAL INFORMATION
• Kinetic energy produced in the huddling chamber causes the valve to pop open.
• Popping pressure is determined by the tension of the spring.
• A safety valve pops to full bore opening which is equal to one quarter of the disk diameter.
(Diameter / 4)
Blowback is determined by altering the distance between the adjusting and nozzle rings.
1. Moving them closer increases blowback moving them apart decreases blow back.
2. The rings are attached by a right hand thread.
3. Move them to the right or anti/clock raises them.
4. Move them to the left or clock lowers them.
5. Major adjustments are made with the adjusting ring; fine tuning with the nozzle ring.
6. If adjustment requires ten notches, valve needs to be overhauled.
• Manual operation of safety to relieve pressure in case of low water is not allowed.
• Waste pipe supports should be examined semiannually.
• Independent economizers (steaming) superheaters and reheaters will be protected by safety
valves but will not be included in the relieving capacity of the boiler.
Safety valve capacity can be formulated by one of three ways:
1. Accumulation test.
2. Measuring the max fuel burn, and computing the evaporating capacity on basis of calorific
value
3. Determining the evaporative capacity on the basis of feedwater flow.

49. • The sum of the relieving capacities of all valves shall be equal or greater than the maximum
evaporative capacity of the boiler.
• Safety valves tests are mandatory at time of boiler inspection. This may be done prior to removing
from service by pinching down on non-return valve until lowest set valve lifts, then open non-return
valve, gag the lowest set valve, then do same for each valve.
• When live testing safety valves, the drum level should be lower than normal, but in safe level.
Safety Valve - Stamping: Each safety valve shall be plainly marked as follows:
1. Manufacturer's identifying mark
2. Manufacturer's design or type number
3. Size..... Seat Diameter....
4. PSI...... (Lifting)
5. Blowdown........
6. Capacity....... lbs/hr
7. Capacity lift.....(Distance valve lifts when blowing at accumulation)
8. Year built
9. ASME symbol

50. • When safety valve fails to open, reduce pressure; try lifting by hand, then raise pressure to
popping point. If it still does not operate, replace it.
• Leaking safety valves should not be gagged. Lift by hand, if it still leaks, replace it.
• Hand lifting safety valves to relieve pressure in a low water situation is not allowed.
• Blow safety valves good after a foaming priming carryover or oil in water situation has been
rectified.
• Bellows type safety valve used in industrial systems where vapor may be corrosive - bellows
protects valve spring and other components.
• Safety relief valves used on heating systems opens slowly at set point. If pressure still increase,
then it will pop.
• Pressure and temperature relief valve used on hot water systems, spring loaded valve and fusible
element.
Testing Intervals:
For Detroit Edison the fossil-fired utility boiler safety valves are to be tested at a regular frequency
determined by their maintenance history. All safety valves shall be tested within the span of two
periodic outages or a maximum of four years.
Power Plant Order #8 – Boiler Safety Valve Testing
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