EXPERIMENT NO. 2
Aim: To study the construction and working of various boiler mountings and accessories. Theory: A boiler is defined as a closed vessel in which steam is produced from water by combustion of fuel. Also defined as “A combination of apparatus for producing, furnishing, or recovering heat together with the apparatus for transporting the heat so made available to the fluid being heated and vaporized.”
Classification of Boilers :
The boilers may be classified according to following criteria: 1.
According to relative position of water and hot gases.
(a) Water tube boiler: A boiler in which the water flows through the tubes which are surrounded by hot combustion gases i.e. Babcock and Wilcox, Stirling, Benson boilers etc.
(b) Fire tube boiler: The hot combustion gases pass through the boiler tubes, which are surrounded by water i.e. Lancashire, Cochran, Locomotive boilers etc.
According to water circulation arrangement
(a) Natural circulation: Water circulates in the boiler due to density difference of hot and cold water e.g., Babcock and Wilcox boiler, Lancashire boiler, Locomotive boiler etc.
(b) Forced circulation: A water pump forces the water along its path, therefore, the steam generation rate increases e.g.. Benson, La Mont, Velox boilers etc.
According to position of furnaces:
(a) Internally fired: The furnace is located inside the shell e.g., Cochran, Lancashire boilers etc.
(b) Externally fired: The furnace is located outside the boiler shell i.e. Babcock and Wilcox, Stirling boilers etc.
According to the use: Stationary, Portable, Locomotive or marine boiler.
According to position of the boilers: horizontal, inclined or vertical boilers.
The boiler mountings are the part of the boiler and are required for proper functioning. In accordance with the Indian Boiler regulations, of the boiler mountings is essential fitting for safe working of a boiler. Some of the important mountings are:
Water level Indicator
Water level indicator is located in front of boiler in such a position that the level of water can easily be seen by attendant. Two water level indicators are used on all boilers. Pressure Gauge
A pressure gauge is fitted in front of boiler in such a position that the operator can conveniently read it. It reads the pressure of steam in the boiler and is connected to steam space by a siphon tube.
The most commonly, the Bourdon pressure gauge is used.
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.
It is very important safety device, which protects the fire tube boiler against overheating. It is located just above the furnace in the boiler. It consists of gun metal plug fixed in a gun metal body with fusible molten metal.
During the normal boiler operation, the fusible plug is covered by water and its temperature does not rise to its melting state. But when the water level falls too low in the boiler, it uncovers the fusible plug. The furnace gases heat up the plug and fusible metal of plug melts, the inner plug falls down The water and steam then rush through the hole and extinguish the fire before any major damage occurs to the boiler due to overheating. 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...
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