This document discusses different types of boilers, including fire tube boilers where hot gases pass through tubes surrounded by water, and water tube boilers where water passes through tubes and hot gases flow outside. It also describes internally and externally fired boilers, high and low pressure boilers, natural and forced circulation methods, boiler mountings for safety and control, and boiler accessories to improve performance like the air preheater, economizer, injector, superheater, and feed pumps.

4. a) Fire tube boiler:
The hot gases passes through the tubes that are surrounded
by water. Fire tube boilers are also known by certain
common names-
 1) Cochran
 2) Locomotive
 3) Lancashire

5. b) Water tube Boiler:
The water passes through the tubes and the hot gases
produced by combustion of fuel, flow outside.
 1) Babcock and Wilcox Boiler

6. a) Internally fired Boilers:
The furnace is provided inside the boiler shell and is completely
surrounded by water cooled surfaces. This method of firing is used
in:
• Lancashire Boilers
• Cochran Boilers
b) Externally fired Boilers:
The furnace is provided outside/ under the boiler. It has an
advantage that its furnace is simple to construct and can easily
be enlarged, as and when required. This method of firing is
used in
• Babcock and Wilcox Boiler.

7. i) High pressure Boilers:
Boilers producing steam 80 bar and above are called High pressure
boilers. E.g.
 Babcock and Wilcox Boiler
ii) Low pressure Boilers:
Boilers producing steam Lower than 80 bar are called Low
pressure boilers. E.g.
• Cochran Boilers
• Cornish Boiler

8. a) Natural circulation method
 Circulation set up by convection current or by gravity.
b) Forced circulation method
 Circulation set up for high pressure steam through
pumps.

16. The necessary devices installed or mounted for the safety of
boiler and its control are called boiler mountings.
The devices which are installed in the boiler for their efficient
operation and smooth working are called Boiler Accessories.

18. 1. WATER LEVEL INDICATOR

19. a) Records gauge pressure
b) Elliptical spring tube is also called
Bourdon tube and is made up of
special quality Bronze.
c) Plug (P) is provided for cleaning
the siphon tube.
d) Siphon is filled with cold water to
prevent the hot steam entering
into the bourdon tube and spring
tube remains comparatively cool.
2. Pressure Gauge

20. 3. SAFETY VALVES
LEVER SAFETY VALVE Dead Weight safety valve

21. High steam & low water safety
valve
Spring loaded safety valve

22. 4. FEED CHECK VALVE
1. It controls the supply of water
to the boiler and prevents the
back flow of water from the
boiler when the feed pump
pressure is less than boiler
pressure of pump is
stopped.

23. 5.BLOW-OFF COCK

24. 6. MANHOLE
 This is provided at suitable position on the boiler shell so that the man can
enter into boiler shell for inspection, maintenance and repairs. This hole is
usually made in elliptical shape of the size convenient for a man to enter
through this hole. The opening is closed by steam tight cover.

25. The devices used to improve the performance
and operation of the boilers are called boiler
accessories. Main accessories used are:

26.  Function:
The function of the air pre-heater
is to increase the temperature of
air before it enters the furnace. It
is generally placed after the
economiser.

27.  Function:
An economiser is a device in
which the waste heat of the flue
gases is utilized for heating the
feed water.

28.  Function:
The function of an injector is to feed water into the boiler. It is also
used where the space is not available for the installation of a feed
pump

29.  Function:
Super heater increases the temperature of the steam above its saturation point. The
steam generated above surface of water is always wet. The main negative effect of
supplying wet steam to turbine or steam engine are erosion of turbine blades,
pipes etc., and condensation losses occurs. Therefore steam must be superheated
before supplying to steam turbine or steam engine.

30.  Function:
Its is a pump which is used to deliver
feed water to the boiler.
 The appliances in common use for
delivering the feed-water into the
steam boilers are:
a) Reciprocating pump
b) Rotary pump