16819_chapter 12 _ boiler mountings _ machine drawing

Machine Drawing

Recommend 6.1k

Press Ctrl & '+' To enlarge text and pics!

Chapters

Home

Topics

Chapter 1 : Basics of Machine

Drawing

Chapter 2 : Theory of Projections

Chapter 3 : Free Hand Sketching

Chapter 4 : Fits and Tolerances

Chapter 5 : Screw Fasteners

Chapter 6 : Riveted and Welded

Joints

Chapter 7 : Assembly Drawings

Chapter 8 : Couplings and

Clutches

Chapter 9 : Cotter and Knuckle

Joints

Chapter 10 : Pipe and Pipe

Fittings

Chapter 11 : I.C. Engine Parts

Chapter 12 : Boiler Mountings

Chapter 13 : Bearings

Chapter 14 : Miscellaneous

Components

Chapter 15 : Computer Drafting

Home

Chapter 12 : Boiler Mountings

12.1 BOILER MOUNTINGS

Different fittings and devices necessary for the operation and

safety of a boiler are called boiler mountings. The various

boiler mountings are:

1. Water level indicator

2. Pressure gauge

3. Steam stop valve

4. Feed check valve

5. Blow-down cock

6. Fusible plug

7. Safety valve : spring loaded, dead weight, lever type.

1. Water Level Indicator

The function of the water level indicator is to indicate the level

of water in the boiler constantly. Every boiler is normally

fitted with two water level indicators at its

front end. Fig. 12.1 shows a water level indicator used in low

pressure boilers. It consists of three cocks and a glass tube.

The steam cock I keeps the glass tube in connection with the

steam space and cock 2 puts the glass tube in convection with

the water space in the boiler. The drain cock 3 is used to

drain out the water from the glass tube at intervals to

ascertain that the steam and water cocks are clear in

operation. The glass tube is generally protected with a shield.

Loremate.com

Like 6,133

Chapter 12 : Boiler Mountings | Machine Drawing http://ptumech.loremate.com/mdr/node/12

1 of 12 1/28/2013 10:44 AM

For the observation of water level in the boiler, the steam and

water cocks are opened and drain cock is closed. The

rectangular passage at the ends of the glass tube

contains two balls. In case, the glass tube is broken, the balls

are carried along its passage to the ends of the glass tube

and flow of water and steam out of the boiler is prevented.

2. Pressure Gauge

The pressure gauge is used to indicate the steam pressure of

the boiler. The gauge is normally mounted in the front top of

the steam drum. The commonly used pressure gauge is the

Bourdon type pressure gauge shown m Fig 12 2 It consists of

an elastic metallic tube of elliptical cross-section bent in the

form of circular arc. One end of the tube is fixed and

connected to the steam of the boiler and other end is

convected to a sector wheel through a link. The section

remains in mesh with a pinion fixed on a spindle. A pointer is

attached to the spindle to read the pressure on a dial gauge.

When high pressure steam enters the elliptical tube, the tube

section tends to become circular which causes the other end

of the tube to move outward. The movement of the closed

end of the tube is transmitted and magnified by the link and

sector. The sector is hinged at a point on the link. The

magnitude of the movement is indicated by the pointer on the

dial.


2 of 12 1/28/2013 10:44 AM

3. Steam Stop Valve

The function of the stop valve is to regulate the flow of steam

from the boiler to the prime mover as per requirement and

shut off the steam flow when not required.

A commonly used steam stop valve is shown in Fig. 12.3. It

consists of main body, valve, valve seat, but and spindle,

which passes through a gland to prevent leakage of steam.

The spindle is rotated by means of a hand wheel to close or

open.

4. Feed Check Valve

The function of the feed check valve is to allow the supply of

water to the boiler at high pressure continuously and to

prevent the hack flow of water from the boiler when the

pump pressure is less than boiler pressure A commonly used

feed check valve is shown in Fig. 12.4. It is fitted to the shell

slightly below the normal water level of the boiler. The lift of

the non-return valve is regulated by the end position of the

spindle which is attached with the hand wheel. The spinfle can

be moved up or down with the help of hand wheel which is

screwed to the spindle by a nut. Under normal conditions, the

non-return valve is lifted due to the water pressure from the

pump and water is fed to the boiler. In case pump pressure

falls below boiler pressure, valve is closed automatically. or

when pump tails.


3 of 12 1/28/2013 10:44 AM

5 Blow-Down Cock

The function of blow-down cock is to remove sludge or

sediments collected at the bottom-most point in the water

space in a boiler, while the boiler is steaming. It is also

used for complete draining of the boiler A commonly used

type of blow- down cock is shown in Fig. 12.5. it consists of a

conical plug fitted accurately into a similar casing. The plug

has a rectangular opening which may he

brought with the line of the passage of the casing by rotating

the plug. This

causes the water to be discharged from the boiler: [he

discharging of water may

be stopped by rotating the plug again.

the blow-down c’k should be opened when the boiler is in

operation br quick

forcing out or sediments for maintenance.

6. Fusible Plug

The main function of the fusible plug is to put off the fire in

the furnace of the boiler when the water level in the boiler

falls below an unsafe level and thus avoid the explosion which

may occur due to overheating of the tubes and shell. The plug


4 of 12 1/28/2013 10:44 AM

is generally fitted over the crown of the furnace or over the

combustion chamber.

A commonly used fusible plug is shown in Fig. 12.6. It

consists of a hollow gun metal body screwed into the fire box

crown. The body has hexagonal flange to lighten it into the

shell. A gun metal plug is screwed into the gun metal body by

tightening the hexagonal flange formed into it. There is yet

another solid plug made of copper with conical top and

rounded bottom. Fusible metal holds this conical copper plug

and the gun metal plug together due to depressions provided

at the mating surfaces.

During normal operation, the fusible plug remains submerged

in water and on no account its temperature can be more than

the saturation temperature of water. Fusible metal is

protected from direct contact with water of furnace gases.

When the water level in the boiler shell falls below the top of

the plug the fusible metal melts due to overheating. Thus the

copper plug drops down and is held within the gun-metal

body by the ribs. Thus the steam space gets communicated to

the fire box and extinguishes the fire. The fusible plug can be

put into position again by interposing the fusible metal.

7. Safety Valves

The function of a safety valve is to prevent the steam

pressure in the boiler exceeding the 4esired rated pressure by

automatically opening and discharging steam to atmosphere

all .Le pressure falls back to normal rated value. There are

three types of safety valves spring loaded (Rams bottom)

type, dead weight type, and lever type.

(a) Spring Loaded Safety Valve


5 of 12 1/28/2013 10:44 AM

The spring loaded safety valve of the Rams Bottom type is

shown in Fig. 12.7. The spring holds the two valves on their

seats by pulling the lever down. The lever is provided with

two conical pivots, one integrally forged with the level and the

other pin connected to one end. The upper end of the spring

is looked to the lever midway between the two pivots. The

lower end is hooked to the shackle fixed to the valve chest by

studs and nuts. The shackle and the lever are also

connected.by two links, one end of which is pin- jointed and

the other end has a slot cut into it to allow for the pin to slide

in it vertically thus allowing the lever to be lifted and retaining

the link connection. These links are provided as a safety

measure in case the spring breaks, the lever should not fly

off. The lever projects on one side for manual operation to

check the satisfactory working of the device.

(b) Dead Weight Safety Valve

In this type of device, shown in Fig. 12.8, the steam pressure in the upward direction is

balanced by the downward force of dead weights acting on the valve. It is generally used

on low capacity boilers like the Lancashire boiler. Bottom flange is directly connected to

seating block on the boiler shell.


6 of 12 1/28/2013 10:44 AM

(c) Lever Safety Valve

A typical lever safety valve is shown in Fig. 12.9. The lever is the second kind with effort

in the middle of fulcrum and load. It is suitable for stationary boilers.

12.2 VALVES

Valves are used to regulate or stop the flow of fluids in a pipe line. The operation of a

valve may be either automatic by fluid pressure or manual by hand. The valves may be

broadly classified as follows


7 of 12 1/28/2013 10:44 AM

1. Flap or Hinged Valve— A flap valve shown in Fig. 12.10 (a) has a flap hinged at

one end. The flap is made of India rubber, leather or fabric. It is a one way valve,

generally used in pump applications as in foot valve, reflux valve, air valve, etc. The

pressure of the fluid from the bottom causes the valve to swing partially out of steam thus

opening the passage for fluid flow. The angular opening of the valve is limited to 32°—40°

by means of some form of stop.

2. Lift Valve—This valve rises vertically from its seat, generally guided. Fig. 12.10 (b)

shows a ball lift valve used in pump applications. The ball may be solid or hollow made of

rubber, bronze or any other metal. Fig. 12.10 (c) shows a disc valve made of India rubber

for pump applications. The valves used in boiler applications such as safety valve, feed

check valve, stop valve, etc. are metal disc valves. These valves are provided with three

or four wings or feathers having straight or spiral shape.

3. Slide valve—The slide valve moves parallel to the seat. In a sluice valve shown in Fig.

12.10 (d), the spring keeps the discs in close contact with the valve seat.

4. Pin, Cock and Throttle valves—These type of valves are shown in Fig. 12.10 (e) to(t).

12.3 LIFT AND MAXIMUM LIFT OF THE VALVE

The lift of the valve is the distance by which the valve moves away from its seat. The

maximum lift of the valve should provide an area of the opening equal to the area of the

passage. This is obtained if the maximum lift, L, is equal to one— fourth of the diameter

of the passage, D.


8 of 12 1/28/2013 10:44 AM

Example 12.1 : The details of a Ramsbottom safety valve are shown in Fig. 12.11.

Draw (a) Right half sectional elevation (b) Sectional side view, and (c) Outside plan

view.


9 of 12 1/28/2013 10:44 AM

Solution The views have been drawn in Fig. 12.12.


10 of 12 1/28/2013 10:44 AM

Example 12.2 Name various boiler mountings.

Solution : 1. Water level indicator

2. Pressure gauge

3. Steam stop valve

4. Feed check valve

5; Blow-down cock

6. Fusible plug

7. Safety valve.

Example 12.3 What is the function of non return valve?

Solution: It allows the supply of water to the boiler at high pressure continuously and

prevents the back flow of water from the boiler when the pump pressure is lower than

the boiler pressure or when pump fails.

Example 12.4 What is meant by the lift of the valve ? What should be the

maximum lift?

Solution: Refer to art. 12.3.

Example 12.5 What is the function of a valve ? Where a feed check valve, is fitted

and what are its functions?

Solution: A valve is used to regulate or stop the flow of fluids in a pipe line. The feed


11 of 12 1/28/2013 10:44 AM

check valve is fitted to the boiler shell slightly below the normal water level of the boiler.

Its function is to allow the supply of water to the boiler at high pressure continuously and

to prevent the back flow of water from the boiler when the pump pressure is less then

boiler pressure or when pump fails.

Example 12.6 What is the function of steam stop valve and give simple sketch.

Solution : The function of steam stop valve is to regulate the flow of steam from the

boiler to the prime moves as per requirement and shut off the steam flow when not

required.


12 of 12 1/28/2013 10:44 AM

16819_chapter 12 _ boiler mountings _ machine drawing

Documents