Boiler Mountings

BOILER MOUNTINGS

For the safe operation, satisfactory functioning, efficient working and easy maintenance of the boilers, Boiler Mountings are provided as per the Indian Boiler Act. These include:

1. Water Gauge (Water Level Indicator)

2. Pressure Gauge

3. Safety Valves

(b) Spring Loaded Safety Valve

(d) High Steam Low Water Safety Valve

4 . Fusible Plug

5. Feed Check Valve

6. Stop Valve

7. Blow-off Cock

1. WATER GAUGE (WATER LEVEL INDICATOR)

It indicates the water level inside the boiler and is hence called Water Level Indicator. Two water gauges are fitted in a boiler as per Indian Boiler Act.

Description (Fig. 5)

It consists of a glass tube, two gun metal tubes and three cocks. The steam cock C₁ is provided on the gun metal tube M₁ which connects the glass tube with the steam space in the boiler. The water cock C₂ is provided on the gun metal tube M₂ which connects the glass tube with the water space. The gun metal tubes M₁ and M₂ are bolted to the boiler shell.

The drain cock C₃ is used to drain the water from the glass tube at intervals to ascertain whether the gauge is in proper order or not. The glass tube is protected by means of a cover, made of specially toughened glass. The cover will prevent any accident that may happen due to the breaking of the glass tube.

Working

The water gauge shows the level of water in the boiler drum. It warns the operator if the water level goes below a fixed mark, so that corrective action may be taken in time to avoid any accident.

. For the observation of the water level in the boiler, the water and steam cocks are opened and the drain cock is closed. The steam enters from the upper metal tube Mi into the glass tube. Also, water enters from the lower metal tube M2 into the glass tube. Hence, water stands in the glass tube at the same level as in the boiler.

The junctions of the metal tubes and the glass tube are provided with two balls. In case the glass tube is broken, the balls are pushed to the top and bottom ends of the glass tube. Thus, the flow of both water and steam out of the boiler is prevented.

2. PRESSURE GAUGE (BOURDON TYPE )

A pressure gauge is used to indicate the steam pressure of the boiler. It is also called Steam Gauge. It is usually mounted in the front top of the steam drum.

Description (Fig. 6): Fig. 6 shows a commonly used pressure gauge known as Bourdon type. It consists of an elastic metallic Bourdon spring tube S. of elliptical cross section and bent in the form of circular arc. One end of the tube is fixed at the block B. It is connected to the steam space of the boiler by means of a cock C.

The other end is connected to a toothed sector T through a link L hinged at the point H. The sector is in mesh with a pinion P fixed on a spindle. An indicating pointer N is attached to the spindle to read the pressure on a dial gauge D.

Working: When steam enters the elliptical tube, the tube section tries to become circular. This causes the other end of the tube to move outward. The movement of the closed end of the tube is transmitted and magnified by link and toothed sector. Magnitude of the movement of the sector is indicated by the pointer on the dial.

Note: Spring tube is surrounded by atmospheric air. So, the pressure in the interior of the tube is above that of the atmosphere, i.e., Absolute pressure = Gauge Pressure + Atmospheric Pressure.

3. SAFETY VALVES

Safety Valves are used to maintain a constant safe pressure inside the boiler. When the pressure inside the boiler increases, the excess steam will escape to the atmosphere through the valve automatically. A boiler is provided with two safety valves as per the Indian Boiler Act.

There are four different types of safety valves, viz., (a) Dead Weight Safety Valve, (b) Lever Safety Valve, (c) Spring Loaded Safety Valve and (d) High Steam Low Water Safety Valve. Spring loaded safety valve is the most commonly used.

a.  Spring Loaded Safety Valve (Ramsbottom Safety Valve)

Description (Fig. 7)

Ramsbottom safety valve is loaded with a spring instead of weights. Hence, it is called Spring Loaded Safety Valve. It consists of a Cast Iron Body having Two Branch Pipes P₁ and P₂.

Two Separate Valves are placed over the valve seatings, which are fixed to the top of the branch pipes. A Lever is placed over the valves by means of two conical pivots.

The lever is attached to a spring at its middle. The spring pulls the lever in downward direction. The lower end of the spring is attached to the valve body by means of a shackle. Thus, the valves are held tight to their seats by the spring force.

Working

When the steam pressure exceeds the normal working pressure in the boiler, the valves rise up against the action of the spring and allow the steam to escape from the boiler till the pressure in the boiler reaches its working pressure.

The spring loaded safety valve is much lighter and compact compared with other safety valves. For locomotive or marine service, the safety valve should be such that it is unaffected by jerks and vibration likely to occur in such device. Hence, spring loaded safety valve is preferred for locomotive and marine services, in addition to stationary boilers.

4. FUSIBLE PLUG

The function of the fusible plug is to put-off the fire in the furnace of the boiler when the water level falls below the normal level. Thus, it avoids the explosion which may take place due to overheating of the tubes and the shell.

Description [Fig. 8]

It consists of a hollow gun metal body screwed into the fire box crown plate. A hollow gun metal plug is screwed into the gun metal body by tightening the hexagonal flange in it.

There is another copper plug locked with the gun metal plug by pouring a low melting point metal (lead) into the groove provided for the same.

Working

During the normal operation, the fusible plug is submerged in water which keeps the temperature of the fusible metal below its melting point.

A But, when the water level falls below the top of the fusible plug, it is uncovered by the water. The fusible plug therefore melts by the heat of the furnace. Thus, the copper plug drops down and is held within the gun metal body by the ribs. The opening so made allows the steam rush into the furnace and extinguish the fire. Thus, damage to the fire box which could burn up, is avoided.