Boiler mountings are necessary for operation and safety of the boiler. These devices are required for complete control of the process of steam generation. The various boiler mountings are
- Water level Indicator: It indicates the level of water in boiler. It consists of a vertical glass tube. Two more horizontal brass tubes are fitted at its upper and lower ends. Upper brass tube is connected to the steam space of the boiler and lower brass tube is connected to the water space of boiler. The upper tube has a steam cock and lower tube has a water cock. A drain cock is provided at the bottom of glass tube for drainage of water and condensed steam from time to time. Under normal working condition, the drain cock remains closed. The water cock and steam cock remain open. The water level with in the boiler is same as that of a glass tube.
Figure: Water level indicator
2. Fusible plug: It protects the boiler from being damaged by overheating due to very low level of water in the boiler. It is fitted in the head plate of the boiler. It consists of a bronze plug with threads at outer surface and a tapered hole in the centre. The hole is filled with a fusible metal. The upper part of the plug remains dipped in water and lower part remains exposed to gases or fire of the furnace. The fusible metal does not melt as it remains in contact with water. When the water level in the boiler falls the upper part of plug is uncovered then the fusible metal melts due to high temperature of steam. The steam from the boiler rushes out from the central hole.
Figure: Fusible Plug
3. Steam stop valve: The stop valve regulates the flow of steam from the boiler to the steam pipe. It is known as junction valve when it mounted on the boiler to control the flow of steam. It acts as a stop valve when it is placed near the engine or between steam pipes. The hand operated steam stop valve consists of a valve spindle which is rotated by a hand wheel. The spindle passes through a screwed portion and then through a gland. The valve rests on valve seat. On rotating the hand wheel if the spindle moves upward the valve is open and it allows the steam to pass. If the lower portion (valve) of the spindle is resting on seat then the valve is closed and it will not allow the passage of steam.
Figure: Steam stop valve
4. Feed check valve: It regulates the flow of water from feed pump to the boiler and prevents the back flow to the feed pump if the pump pressure is less than the boiler pressure. It allows the flow of water in only one direction. It is placed in between the boiler and the feed pump. A typical feed check valve is shown in the figure. At normal condition, the valve may be lifted up as the water is fed into boiler from feed pump. When the feed pump stops working, the valve may be closed (on its seat).
Figure: Feed check valve
5. Blow off cock: It is fitted directly or to a pipe to the lowest part of the boiler. It is necessary to empty the boiler and clean it periodically. The sediments settled at the bottom of the boiler shell can be taken out by discharging a portion of water. A common type of blow off cock is shown in the figure. It consists of a plug having rectangular opening. When we want to discharge the water, the hand wheel is rotated to bring the opening in line with the passage of water. This results in discharging of water. The hand wheel may be rotated again to stop the flow of water.
Figure: Blow off cock
6. Safety Valve: The function of safety valve is to maintain the pressure in the boiler within the working limit. It automatically discharges extra steam if the pressure inside the boiler exceeds the working pressure. There are four types of safety valves.
(i) Dead weight safety valve: A heavy weight is used to keep the valve on its seat.
(ii) Lever safety valve: A weight is attached to the end of lever to keep the valve on its seat.
(iii) Spring loaded safety valve: Spring force is used to keep the valve on valve seat.
(iv) High steam and low water safety valve: A hinged lever having weights and a float to lift the valves is used.