Water tube boilers have water flowing inside tubes and gases circulating outside. They are used for high steam demands and pressures between 4,000-120,000 kg/hour. Water tube boilers have higher efficiency and steam generation capacity than fire tube boilers due to their design with water inside tubes and gases outside providing better heat transfer. They require pure feed water and more maintenance than fire tube boilers.

1. Water Tube Boilers
 In this type of boiler water passes through the tubes while the
gases remain in the shell side, passing over the tube surfaces
• Used for high steam demand and pressure requirements
• Capacity range of 4,000 – 120,000 kg/hour

2. Water
tube
boilers

3. Difference bw water tube & fire
tube boiler
 Water tube.
 Water circulate inside the tubes.
 Steam generation capacity is high.
 Higher efficiency.
 It has greater heating surface.
 Its cleaning is easy.
 Its shape is drum type.
 Each type of fuel is burned in it.
 Transportation is easy from one place to other.

4. Fire tube boiler
 Fire circulate inside the tubes.
 Steam generation capacity is lower then water tube.
 Lower efficiency.
 Shell type.
 Complicated in design.
 Heating surface is less.
 Cleaning is difficult.
 Specific fuel is used.

5. Parts of water tube boiler

6. BOILER MAIN COMPONENTS
 BOILER SHELL- The outer
cylindrical portion of a pressure vessel.
 BURNER - A device for the
introduction of fuel and air into a
furnace at the desired velocitie.The
burner is the principal device for the
firing of oil and/or gas.

7. BOILER MAIN COMPONENTS
 Mud Ring or Mud Drum
 A typically cylindrical shaped
space at the bottom of the water
space. Sediment, mud, and other
impurities gather there.
 FURNACE - An enclosed space
provided for the combustion of
fuel.

8. BOILER MAIN COMPONENTS
 SAFETY VALVE - A spring loaded
valve that automatically opens when
pressure attains the valve setting.
Used to prevent excessive pressure
from building up in a boiler.

9. BOILER MAIN
COMPONENTS
 STRAINER - A device, such as
a filter, to retain solid particles
allowing a liquid to pass.
 SIGHT GLASS- A glass tube
used on steam boilers to give a
visible indication of the boiler's
water level

10. BOILER MAIN COMPONENTS
 Feed Check Valve. The
high pressure feed water is
supplied to the boiler
through this valve. This
valve opens towards the
boiler only and feeds the
water to the boiler.
 Steam Stop Valve.
 It regulates the flow of
steam supply outside.

11. Type of water tube boiler
 Simple vertical boiler
 A vertical boiler is a type of water-
tube boiler where the boiler barrel
is oriented vertically instead of the
more common horizontal
orientation. Vertical boilers were
used for a variety of steam-
powered vehicles and other mobile
machines, including early steam
locomotives.

12. Type of water tube boiler
 Stirling boiler
 The Stirling boiler is an early
form of water-tube boiler, used to
generate steam in large land-
based stationary plants.
 Stirling boilers are one of the
larger arrangements for a water-
tube boiler. They consist of a
large brick-built chamber with a
sinuous gas path through it,
passing over near-vertical water-
tubes that zigzag between
multiple steam drums and mud
drums.

13. Type of water tube boiler
 Babcock and Wilcox boiler
 The longitudinal drum boiler
is the generally accepted
standard of Babcock &
Wilcox construction. The
cross drum boiler, though
originally designed to meet
certain conditions of
headroom, has become
popular for numerous classes
of work where low headroom
is not a requirement which
must be met.

14. MERITS OF WATER TUBE BOILERS
OVERFIRE TUBE BOILERS
 1. Generation of steam is much quicker due to small
ratio of water content to steam content. This also helps
in reaching the steaming temperature in short time.
 2. Its evaporative capacity is larger and the steam
pressure range is also high-200 bar.
 3. Heating surfaces are more effective as the hot gases
travel at right angles to the direction of water flow.

15. MERITS OF WATER TUBE BOILERS
OVERFIRE TUBE BOILERS
 4. The combustion efficiency is higher because complete
combustion of fuel is possible as the combustion space is
much larger.
 5. The thermal stresses in the boiler parts are less as
different parts of the boiler remain at uniform temperature
due to quick circulation of water.
 6. The boiler can be easily transported and easily its
different parts can be separated.

16. MERITS OF WATER TUBE BOILERS
OVERFIRE TUBE BOILERS
 7. All parts of the water tube boilers are easily accessible
for cleaning, inspecting and repairing.

17. Demerits :
 1. It is less suitable for impure and sedimentary water, as a
small deposit of scale may cause the overheating and
bursting of tube. Therefore, use of pure feed water is
essential.
 2. They require careful attention. The maintenance costs
are higher.
 3. Failure in feed water supply even for short period is
liable to make the boiler over-heated.