BOILER MOUNTINGS

1.         Blow-Off Cock

 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.

Hence it is mounted at the lowest part of the boiler. When it is open, water under the pressure rushes out,

thus carrying sediments and mud.

2.         Fusible plug

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 mean of spanner on the top of the yoke,

 two vertical slots are provided for fixing spanner.

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.

 It is use to protect the boil against damage due to overheating caused by low water level in the boiler.

It is fitted on the fire box crown plate or over the combustion chamber. The fusible plug consist of two hollow guns

 and one conical plug. A hollow gun metal body is screwed to the fire box crown plate of boiler. Another hollow

gun metal is screwed to the first body. Third plug is made from copper is locked with second plug by pouring metal

 in to the grooves provided on the both plugs.

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

 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 uncovered by the water and get exposed to steam. This overheats the plug and

the fusible metal having low melting point which 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.

3.         Feed check valve:

Function: It controls the supply of water from the boiler when the feed pump pressure is less than boiler pressure or pump

 is stopped. The feed check valve is fitted in water space of the boiler just below the normal level of the water.

 It consist of non-return valve, water inlet pipe, out let pipe, spindle, gland and wheel. The outlet pipe of valve connected

 with and of delivery pipe of feed pump.

Inlet and outlet pipe of valve expose different pressure. At inlet of valve, the feed pump pressure acts and outlet pipe of the

 valve the boiler pressure act . When 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.

4.       Water level gauge:

It indicates the water level inside the boiler vessel. It shows the level in the boiler drum. Normally two water level indicator

 are fitted to the boiler. These are fitted at the front end of every boiler. Water level indicator consist three cocks as steam cock,

water cock, drain cock and glass tube. The steam cock connects or disconnects the glass tube with steam space. While water cock

 connects or disconnects the glass tube with water in the boiler. The drain cock is used to drain out the water in from glass tube at

interval to ensure that the steam and water cock are clear in operation. The glass tube protected by means of a cover, and made

of specially.

       When steam cock and water cock opened, steam rushes from upper passage and water rushed from lower passage to the glass tube.

This will indicate the level of water in the boiler. Two balls are places at the junction of metal tube. Under normal operating

Conditions the balls are kept full line circle. 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 balls are carrier along the passage to

 and of glass tube and then closed passages. Thus flow of water and steam out of boiler is prevented.

5.         Steam Stop Valve:

 It regulates the flow of steam from boiler to the steam pipe or from one steam pipe to the other.

 The flange of valve body bolted to the boiler at the highest part of steam space. It consists of valve seat and nut.

 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 connected to valve upper and pass through gland and yoke,

 and connected with hand wheel. The gland is used to prevent the leakage of steam.

The spindle it rotated by help of hand wheel due to rotation of spindle the valve move up and 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 moving

the valve up, help of rotating the hand wheel the clearance (passage) between valve and valve seat regulates the flow of steam

 out of boilers.

6.         Pressure Gauge:

 It indicates the pressure of steam in boiler.

 The gauge is usually mounted on the front top of the shell or on the drum. It is having dial which graduated to read pressure

in bar, above atmosphere. A bourdon tube gauge with its interior mechanism is provided commonly. 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 quadrant with help of link and pin. This quadrant meshes with a small

 pinion on the central spindle.

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.

7.         Safety Valves:

 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 pressure of steam in the boiler drum exceeds the working pressure then the safety valve allows blow-off

the excess quantity of steam to atmosphere. Thus the pressure of steam in the drum falls. The escape of steam makes

a audio noise to warm the boiler attendant.

There are four 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