Fire tube boiler – – flames and hot gases produced by combustion of fuel pass through the tubes which are surrounded by the water.
Water tube boiler – – water is contained inside the tubes which are surrounded by flames and hot gases from outside.
Important terms for steam boilers:
1.1. Boiler shell: it is made up of steel plates bent into cylindrical from reverted or welded together.
A boiler shell should have sufficient capacity to contain water and steam.
2.2. Combustion chamber: It is the space generally below the boiler shell, meant for burning fuel in
order to produce steam from the water contained in the shell.
3.3. Gate: It is the platform in the combustion chamber, upon which fuel is burnt. The gate, generally
consist of cast iron bars which are spaced apart so that air can pass through them. The surface
are of the gate over which the fire takes place is called gate surface.
4.4. Furnace – – It is the space above the gate and the boiler shell in which the fuel is actually burnt
the furnace is also called as firebox.
5.5. Heating surface: It is that part of boiler surface which exposed to the fire.
6.6. Mountings: There are the fittings which are mounted on the boiler for its proper functioning. A
boiler cannot function safely without mountings. Through there are many types of boiler
mountings yet the following are important from the subject point of view.
A)A) Water level indicator
B)B) Pressure gauge
C)C) Safety valve
D)D) Blow off cock
E)E) Feed check valve
F)F) Fusible plug
G)G) Blow down valve
(a)(a) Water indicator: It is an important fitting which indicate the water level inside the boiler to an
observer.
(b)(b) Pressure gauge: A pressure gauge is used to measure the pressure of the steam boiler. It is fixed
in front of the steam boiler.
(c)(c) Safety valves There are the devices attached to the steam chest for preventing explosions due to
excessive internal pressure of steam. There are 4 types of safety valves: i. Lever safety valve
ii. Dead weight safety valve
iii. High steam and low water safety valve
iv. Spring loaded safety valve
(d) Stop valve: It is the largest valve on the steam boiler. It is used to control the flow of steam from
boiler to the main steam pipe.
(e) Blow off cock: It is fitted to the bottom of a boiler drum and consists of a conical plug fitted to
the body or casting. Its function is to empty the boiler whenever required and to discharge the
mud, scale or sediments which are accumulated at the bottom of the boiler.
(f) Feed check valve: Itt is a non return valve fitted to a screwed spindle to regulate the lift. Its
function is to regulate the supply water which pumped into the boiler by the feed pump.
(g) Fusible plug: It is fitted to the crown plate of the furnace or the fire. Its objective is to put off the
fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit thus
avoids the implosion which may take plae due to overheating of the furnace plate.
(h) Blow down valve: It is fitted to the lower side of the boiler. Its function is to reduce the
impurities of the boiler.
7. Accessories: These are the devices which form an integral part of a boiler but are not mounted
on it. It may be noted that the accessories help in controlling and running the boiler efficiency.
Though there are many types of accessories yet the following are important from the subject
point of view
a. Feed pump
b. Superheater
c. Economizer
(a) Feed pump: A feed pump is needed to deliver water to the boiler. The pressure of feed water is
20% more than that in the boiler. The feed pump may be classified as simplex, duplex, triplex
pumps according
Fuel system
Fuel feed systems play a critical role in the performance of boilers. Their primary functions include transferring the fuel into the boiler and distributing the fuel within th boiler to promote uniform and complete combustion. The type of fuel influences the operational features of a fuel system. Feed system for gaseous fuels
The main components in a boiler system are boiler feedwater heters, deaerators, feed pump,