Lecture on Boiler mountings and accessories delivered at SNIST Hyderabad

1. BOILER
MOUNTINGS AND ACCESSORIES
Dr. Mohammad Shaukat Ali, SNIST, Hyderabad, India

2. BOILER MOUNTINGS AND ACCESSORIES
2
MOUNTINGS
Boiler Mountings are the components generally mounted on the
surface of the boiler for its safe and secured operation. These are the
essential parts of the boiler, without which the boiler operation is not
possible.
ACCESSORIES
These are the devices which are installed with a boiler and its
neighboring area to increase the efficiency of the boiler. These are not the
essential part of the boiler and thus without installing these devices, the
boiler operation can be accomplished though at a lower efficiency.

3. 3
BOILER MOUNTINGS

4. 4
Indian boiler regulation recommends the following mountings to be
fitted with the boiler –
 Two safety valves
 Two water level indicators
 A pressure gauge
 A steam stop valve
 A feed check valve
 A blow-off cock
 An attachment for inspector’s test gauge
 A man hole
 Mud holes or sight holes.
Note: Apart from the above all land boilers should have fusible plug in
each furnace
BOILER MOUNTINGS

5. 5
Blow-off cock
BOILER MOUNTINGS
FUNCTION
• The function of blow-off cock is to
discharge mud and other sediments
deposited in the bottom most part of
the water space in the boiler, while
boiler is in operation.
• It can also be used to drain-off boiler
water for cleaning and maintenance
purpose. Hence it is mounted at the
lowest part of the boiler. When it is
opened, water under the pressure
rushes out along with the sediments
and mud.

6. 6
Blow-off cock
BOILER MOUNTINGS
CONSTRUCTION
• It is fitted on the boiler shell directly or
through the short branch of pipe at lowest
part of the water space.
• It consists of gun metal conical plug
having a rectangular hole, spindle with
yoke.
• The plug meshes accurately into the
similar casing.
• The plug spindle is generally rotated by
means of spanner on the top of the yoke.
• Two vertical slots are provided for fixing
spanner.

7. 7
Blow-off cock
BOILER MOUNTINGS
WORKING
• When rectangular hole of plug is brought
in line with casing hole by rotating
spindle, the water flow out.
• When the solid portion of the plug is in
front of casing hole the water cannot flow
out of boiler.

8. 8
Fusible plug
BOILER MOUNTINGS
FUNCTION
• It is used to protect the boiler from
damage due to overheating caused
by low water level in the boiler.
CONSTRUCTION
• It is fitted on the fire box crown
plate that separates the boiler shell
and combustion chamber.
• The fusible plug consist of two
hollow gun metal body and one
conical plug as shown in the figure.
• First hollow gun metal body is screwed to the fire box crown plate of
boiler. Second hollow gun metal is screwed on the first body. Third plug is
normally made from copper is locked with second plug by pouring low
melting point metal in to the grooves provided on both of the plugs.

9. 9
Fusible plug
BOILER MOUNTINGS
WORKING
• In normal working condition, the upper surface of
fusible plug is covered with water which keeps the
temperature of the plug below its melting point while
other end of plug is exposed to fire or hot gases.
• The low melting point metal joining the second and
third plug does not melt till the upper surface of plug
is submerged in water.
• But in case of water level in boiler falls below the
danger levels, the fusible plug become uncovered by
the water and get exposed to steam. This overheats the
plug and the fusible metal having low melting point
melts quickly. Thus the third plug drops down and
second hollow gun became open, the steam rushes into
the furnace and puts out the fire.

10. 10
Feed check valve
BOILER MOUNTINGS
FUNCTION
• It controls the supply of water to the boiler
and to prevent escaping of water from the
boiler when the feed pump pressure is less
than boiler pressure or pump is stopped.
CONSTRUCTION
• The feed check valve is fitted in water
space of the boiler just below the normal
level of the water.
• It consists of non-return valve, water inlet
pipe, outlet pipe, spindle, gland and wheel.
• The inlet of the valve is connected with the
feed pump where as the outlet is connected
with the boiler.

11. 11
Feed check valve
BOILER MOUNTINGS
WORKING
• Inlet and outlet pipe of the valve are exposed to
different pressure when pump is in operation.
At inlet of valve the feed pump pressure acts
where as at outlet pipe of the valve the boiler
pressure acts.
• When the feed pump is in operation the
pressure on the feed pump side (inlet) is more
than pressure on the boiler side (outlet). This
pressure difference lifts the non return valve,
and allows water flow into boiler.
• When the pump stops working, the pressure on
the pump side is less than the boiler pressure
causing the valve to close automatically.

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Water Level Indicator
BOILER MOUNTINGS
FUNCTION
• The function of the water level
indicator is to indicate the level of
water in the boiler constantly.

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Water Level Indicator
BOILER MOUNTINGS
CONSTRUCTION
• Normally two water level indicator are fitted in the front of every boiler.
• Water level indicator consists of three cock - steam cock, water cock,
drain cock and glass tube.
• The steam cock connect or disconnects the glass tube with steam space.
while water cock connect or disconnect the glass tube with water in the
boiler.
• The drain cock is used to drain out the water from glass tube at intervals
to prevent the accumulation of sediments.
• The glass tube protected by means of a guard glass. It is tough and does
not give splinters on breaking.

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Water Level Indicator
BOILER MOUNTINGS
WORKING
• When steam cock and water cock opened, steam rushes from upper
passage and water rushed from lower from passage to the glass tube.
This will indicate the level of water in the boiler.
• Two ball are places at the junction of metal tube. Under normal
operating condition the ball are kept as it is.
• In case the glass tube is broken, steam will rushes from upper passage
and water from lower passage due to pressure difference between boiler
pressure at atmospheric pressure. the ball are carrier along the passage
up to the ends of glass tube and then close the passages. This position of
ball sown in fig by dotted circle. Thus flow of water and steam out of
boiler is prevented.

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BOILER MOUNTINGS
Steam Stop Valve
FUNCTION
• The function of the Steam Stop
Valve to regulate the flow of steam
from boiler to the steam pipe or
from one steam pipe to the other
steam pipe.

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BOILER MOUNTINGS
Steam Stop Valve
CONSTRUCTION
• Commonly the flange of valve body is
bolted to the boiler at the highest part of
steam space.
• It consist of valve and valve seat. The
main body of valve is made of cast iron
and valve seat made from gun metal.
• When steam stop valve is placed directly
over the boiler and connected to the
steam pipe line is called the junction
valve. If it is placed near to prime mover
than normally called steam stop valve.
• The lower ends of spindle is connected to the valve and pass through
gland and yoke, and connected with hand wheel. The gland is used to
prevent the leakage of steam.

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BOILER MOUNTINGS
Steam Stop Valve
WORKING
• When the spindle is rotated by help of hand
wheel the valve can be moved up or down.
• When the valve sits over the valve seat, the
passage of steam is completely closed.
• The steam passage may be partially or fully
opened by rotating the hand wheel.
• The clearance between valve and valve seat
regulates the flow of steam out of boilers.
• In locomotive boilers, the supply of the
steam is regulated by means of a regulator
which is placed inside boiler cell and
operated by a handle from driver’s cabin.

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BOILER MOUNTINGS
Pressure Gauge
FUNCTION
• Pressure gauge is used to measure the pressure of steam inside the
boiler vessel.

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BOILER MOUNTINGS
Pressure Gauge
CONSTRUCTION
• The gauge is usually mounted on the front
top of the shell.
• It is having dial which graduated to read
gauge pressure in bar.
• The circular bent bourdon tube of oval-
cross section is close at one end and
connected at the other end to steam space
of boiler through siphon (U-tube).
• The siphon is filled with water which
prevents hot steam from entering the
pressure gauge and keeps the gauge cool.
• Closed end of bourdon tube is attached to a toothed rack with help of link and
pin. This quadrant meshes with a small pinion on the central spindle.
• A needle is attached to the spindle which can rotate along with the pinion.

20. 20
BOILER MOUNTINGS
Pressure Gauge
WORKING
When pressure is applied to inside of
oval bourdon tube. It cross section
tends to becomes circular, and free end
of bourdon tube try to becomes
straight, so turning the spindle by the
links and gearing. This causes the
needle to move and indicate pressure
on graduated dial.

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BOILER MOUNTINGS
Safety Valve
FUNCTION
• Safety valves are located on the top of the boiler.
• They guard the boiler against the excessive high pressure of steam
inside the drum.
• If the steam pressure inside the boiler drum exceeds the working
pressure limit then the safety valve allows to blow-off the excess
quantity of steam to atmosphere thereby decreasing the pressure.
• The escape of steam makes a audio noise to warm the boiler
attendant.

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BOILER MOUNTINGS
Safety Valve
Types of safety valve:
1. Dead weight safety valve
2. Spring loaded safety valve
3. Lever loaded safety valve
4. High steam and low water safety valve

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BOILER MOUNTINGS
Dead weight safety valve
CONSTRUCTION
• It consists of valve V is placed upon a valve
seat VS which is fix upon a long vertical cast
iron pipe A having a flange B at the bottom
for fixing at the top of the boiler.
• The weight carrier WC suspended from the
top of the valve which carries cast iron
weights W.
• The cover plate C covers the weight.
• The pressure applied by the total weight
(weights+valve+weight carrier+cover plate)
on the valve must be slightly less than or
equal to the maximum allowable pressure in
the boiler.

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BOILER MOUNTINGS
Dead weight safety valve
WORKING
• When the steam pressure exceeds the
normal limits, this high pressure stream
creates upward force on valve, thus valve
V lift with its weights and the excess
steam escapes through the pipe to the
outside.
• The construction of this valve is simple
and gives satisfactory operation for low
pressure and stationary boilers.
• It is not suitable for moving boilers as the
force of the weights should always work
vertically downward.
• It is also not suitable for high pressure
boiler as the weight becomes to large.

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BOILER MOUNTINGS
Lever safety valve
CONSTRUCTION
• It consist of a lever and weight W.
• The valve (made of gun metal) rests on the valve seat (made of gun metal) which is
screwed into the valve body.
• The valve body is fitted on the boiler shell. One end of the lever is hinged while at
the other end a weight W is suspended.

26. 26
WORKING
• The steam presses against the valve on the valve seat.
• The slotted lever guide allows vertical movement to the lever.
• When the steam pressure becomes greater than the normal working pressure, the
valve is lifted with the lever and the weight. Consequently, the steam escapes
through the passages between the valve and seat and the steam pressure decreases.
• The disadvantages of this valve is that it can easily be tampered with and the effect
of a small addition to the weight is magnified considerably in its action on the valve.
BOILER MOUNTINGS
Lever safety valve

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BOILER MOUNTINGS
Spring loaded safety valve
CONSTRUCTION AND WORKING
• For locomotives and marine engines
both the lever and dead weight type
valves are unsuitable for obvious
reasons and the valve must be spring
loaded, as such valve is unaffected by
vibration or deviations from the
vertical.
• The figure shows a Ramsbottom
spring loaded safety valve.
• It consist of two separate va1ves and
valve seats having one lever, bearing
on the two valves, and loaded by a
spring, the spring being placed
between the valves.

28. 28
BOILER MOUNTINGS
Spring loaded safety valve
CONSTRUCTION AND WORKING …
• By pulling or raising the lever the
operator/driver can relieve the pressure
from either valve separately and
ascertain it is not sticking on the
seating.
• One disadvantage of the spring loaded
safety valve is that the load on the
valve increases as the valve lifts due to
increased spring stiffness, so that
pressure required just to lift the valve is
less than that required to open it fully.
• From this reason in some cases it is
arranged that the area acted on by the
steam is greater when the valve is open
than that when the valve is closed.

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BOILER MOUNTINGS
High steam &
low water safety valve
W1 = Main weight
W2 = Counter weight
L1, L2 = Levers
V = Valve
U = Hemispherical valve
VS = Valve seat
F1 = Fulcrum (upper lever L1)
F2 = Fulcrum (upper lever L2)
E = Float
K = Knife edge
C = Spindle
w = Dead weight
W = Balanced weight
Hopkinson’s high steam
& low water safety valve

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BOILER MOUNTINGS
High steam & low water safety valve
CONSTRUCTION AND WORKING
• This is a single device in which two valves are combined in one to serve the
following purposes:
(1) The steam automatically escapes out when the level of water falls below a
certain level.
(2) It automatically discharges the excess steam when the pressure of the steam
rises above a certain pressure.
• It is generally used on 1ancashire or Cornish boilers. It cannot be used on mobile
boilers.
• It consists of valve V resting on the valve seat VS and the valve U loaded with the
weights w rests on the valve V.
• Now, when the steam pressure rises above the rated pressure of the boiler, the valve
V is uplifted along with the valve U and the steam escapes out.
• Therefore, in case when the steam pressure exceeds the rated pressure, top valve
acts as a lever safety valve.

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BOILER MOUNTINGS
High steam & low water safety valve
CONSTRUCTION AND WORKING …
• The most important arrangement is lever L2 with the fulcrum F2. On one end it is
attached to a float E, usually made of tile and on the other end it attached to a fixed
balance weight W.
• When the float E is submersed in water, the lever L2 is balanced about fulcrum F2.
• When the water level falls below a certain level, the weight of the float E increases
and it produces a swing towards the right so that the knife edge K lifts the spindle C
which opens the valve U and thus the steam rushes out.

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BOILER ACCESSORIES

33. 33
BOILER ACCESSORIES
Commonly used boiler accessories are -
 Feed pump
 Injector
 Economiser
 Air preheater
 Superheater
 Steam separator
 Steam trap

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BOILER ACCESSORIES
Feed Pumps
FUNCTION
• The feed pump is a pump which is used to deliver feed water to the
boiler.
• It is desirable that the quantity of water supplied should be at least
equal to the evaporated steam supplied to the engines.

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BOILER ACCESSORIES
Feed Pumps
CLASSIFICATION
• Two types of pumps which are commonly used as feed pumps are
(i) reciprocating pump, and (ii) rotary pump.
• The reciprocating pump consists of a cylinder and a piston. The piston
reciprocates inside the cylinder displacing water.
Reciprocating pump
• The reciprocating pump may be of two types:
a. Single acting pump b. Double acting pump .
• In a single acting pump the water is displaced by one side of the piston only
and so the water is discharged in alternate strokes.
• In a double acting pump, the water is discharged in each stroke of the piston
since the water is displaced by both the sides of the piston.
• The reciprocating feed pumps are continuously run by steam from the same
boiler to which water is to be fed.

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BOILER ACCESSORIES
Feed Pumps
CLASSIFICATION ...
Rotary pump
• Rotary feed pumps are of centrifugal type and are commonly run either by a
small steam turbine or by an electric motor.
• A rotary pump consists of a casing and a rotating element known as impeller
which is fitted over a shaft. It utilizes the centrifugal force of the rotating
impeller for pumping the liquid from one place to the other.

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BOILER ACCESSORIES
Feed Pumps
• The figure shows a duplex direct acting steam pump in which two single steam
cylinders are placed side by side. Slide valves distribute the steam in each cylinder.
The slide valve in each cylinder steam chest is operated by the crosshead on the
piston rod of the opposite cylinder through an arrangement of rods and rocker arms.
• The feed pump is generally double acting. On each side of the pump plunger there
are suction and discharge valves. The pumps work alternately and consequently
continuous flow of water is maintained. Double feed pump is commonly employed for
medium size boilers.

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BOILER ACCESSORIES
Feed Pumps

39. 39
BOILER ACCESSORIES
Steam Injector
FUNCTION
• The function of an injector is to feed water into the
boiler.
• In an injector the water is delivered to the boiler by
steam pressure; the kinetic energy of steam is used
to increase the pressure and velocity of the feed
water.
• It is commonly employed for vertical and
locomotive boilers
• It is also used where the space is not available for
the installation of a feed pump.
• It is not suitable for large capacity high pressure
boilers.

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CONSTRUCTION
• It consists of a spindle P, a steam cone S, a
combining cone K, a delivery cone D, and a
handle H with a pointer T.
• The spindle’s upper end is provided with a
handle H while the lower end serves the purpose
of a valve.
• The pointer on the handle indicates the ‘shut’
and ‘open’ position of the valve.
• The lower part of the spindle has a screw which
works in a nut which is integral part of the steam
cone. The key E checks the rotation of steam
cone.
BOILER ACCESSORIES
Steam Injector

41. 41
WORKING
• With the rotation of the handle steam cone moves
up or down and consequently the valve controls the
steam flow through the steam cone. The steam
enters through the steam pipe A, while the feed
water enters through the water pipe B.
• The flow of water is also regulated due to sliding
motion of the steam cone by its lower end. The
water mixes with the steam at the combining cone K
where it is condensed.
• The mixture then passes through the delivery cone
D and there its kinetic energy is converted into
pressure energy.
• The final pressure must be greater than the steam
pressure of boiler otherwise water will not enter
into the boiler.
• The excess water finds its way through the overflow
pipe C.
BOILER ACCESSORIES
Steam Injector

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ADVANTAGES
1. Low Initial cost
2. Simplicity
3. Compactness
4. Absence of dynamic parts
5. High thermal efficiency (about 99%)
6. Ease of operation.
DISADVANTAGES
1. Pumping efficiency is low
2. It cannot force very hot water
3. Irregularity of operation under extreme variation in steam pressure
BOILER ACCESSORIES
Steam Injector

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BOILER ACCESSORIES
Economiser
FUNCTION
Economiser increases the
temperature of feed water
using waste of heat to flue
gases that leaves the boiler.

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BOILER ACCESSORIES
Economiser
CONSTRUCTION AND WORKING
• The figure shows an independent type vertical tube Economiser (called Green’s
Economiser).
• It is employed for boiler of medium pressure range of up to about 25 bar.
• It consists of a large number of vertical cast iron pipes P through which feed
water is made to pass with the help of top and bottom main pipes A and B.
• The flue gases move around the pipes resulting in heat transfer to the feed water
through the surfaces of the pipes.
• The soot of the flue gases which gets deposited on the pipes over time reduces
the efficiency of the Economiser.
• To prevent the soot deposit, the scrapers S can be moved up and down to keep
the external surfaces of the pipes clean.

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BOILER ACCESSORIES
Economiser
ADVANTAGES
• The temperature range between various part of the boiler is reduced which results
in reduction of tresses duo to unequal expansion
• If the boiler is fed with cold water it may result in chilling the boiler metal.
• Hot feed water reduces the thermal stresses that may be otherwise be caused due
to feeding of cold water.
• Evaporative capacity of the boiler is increased.
• Overall efficiency of the plant is increased.

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BOILER ACCESSORIES
Superheater
FUNCTION
• The function of a Superheater is to increase the temperature of the steam above its
saturation point.
• The superheater is very important accessory of a boiler and can be used both on
fire tube and water-tube boilers.
• Superheaters are located in the path of the furnace gases so that heat is recovered
by the superheater from the hot gases.
• Superheaters are not of much use for the small boilers.
ADVANTAGES
(1) Steam consumption of the engine or turbine is reduced.
(2) Losses due to condensation in the cylinders and the steam pipes are reduced.
(3) Erosion of turbine blade is eliminated.
(4) Efficiency of the steam plant is increased.

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BOILER ACCESSORIES
Superheater
CONSTRUCTION & WORKING
• Above figure shows Sugden’s superheater for Lancashire boiler.
• It consists of two steel headers to which around forty steel ‘U’ tubes are attached.
• The steam from the boiler enters and leaves the headers via large number of small
diameter steel U tubes exposed to hot flue gases.

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BOILER ACCESSORIES
Air Preheater
FUNCTION
• The function of the air preheater is to
increase the temperature of air before it is
supplied to the furnace.
• Objective is to assist the combustion and
increase the thermal efficiency of the
process.

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BOILER ACCESSORIES
Air Preheater
CONSTRUCTION AND WORKING
• Air Preheater is generally placed after the
Economiser in the path of the flue gasses.
• It consists of large number of tubes
through which the flue gases are made to
pass.
• The inlet air at room temperature is
admitted into the shell and passes around
the tubes before leaving the shell as
heated air.

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BOILER ACCESSORIES
Further study: Steam Separator, Steam Trap
End