Murshidabad Institute of Technology
Cossimbazar, Berhampore
Dist.: Murshidabad, West Bengal
DEPARTMENT OF MECHANICAL ENGINEERING
Experiment
TO STUDY COCHRAN BOILER
NAME:
ROLL NO.:
SIGNATURE OF THE STUDENT:
DATE OF SUBMISSION:
STUDY OF BOILER
Name Of The Boiler: Cochran Boiler
SPECIFICATION OF THE BOILER
Type Of The Boiler : Fine tube Boiler
Steaming Capacity : 3500 kg/hr (max capacity 4000 kg/hr)
Pressure Limit : 6.5 ban (max pressure 15 ban)
Size :
i. Diameter of the drum :- 2.75 m.
ii. Length :-
iii. Height :- 5.79 m.
Efficiency : 70% to 75% (depending on the fuel used).
Mountings :
i. Steam Stop Valve
ii. Spring Loaded Safety Valve
iii. Pressure Gauge
iv. Water Level Indicator
v. Fusible Plug
COCHRAN BOILER
There is various design of vertical multi tubular boilers. A Cochran Boiler is considered to be one of
the most efficient types of such boilers. It is an improved type of simple vertical boilers.
This boiler consists of an external cylindrical shell and a fine box as shown in fig. The shell and fine box are
both hemispherical. The hemispherical crown of the boiler shell gives maximum space and strength to
withstand the pressure of steam inside the boiler. The hemispherical crown of the fine box and combustion
chamber is connected through a short pipe. The flue gases form the combustion chamber flow to the smoke
box through a number of smoke tubes. These tubes generally have 62.5 mm. of external diameter and are 165
in number. The gases from the smoke box pass to the atmosphere through a chimney. The combustion chamber
is lined with fine bricks on the shell side. A manhole near the top of the crown on the shell is provided for
cleaning.
At the bottom of the fine box, there is a grate and the coal is fed through the fine hole. If the boiler is used for
oil fining grate is provided, but the bottom of the fine box is lined with fine bricks. The oil burner is fitted at
the fine hole.
MOUNTING
STEAM STOP VALVE:
It is the largest valve on the steam boiler. It is usually fitted to the highest part of the shell by the means of a
flange as shown in fig. The principle function of a stop valve are :
1. To control the flow of the steam from the boiler to the main steam pipe.
2. To shut off the steam completely when required.
The body of the stop valve is made of cast iron or cast steel. The valve, valve seat and nut through which the
valve spindle works, are made of brass and gun metal.
PRESSURE GAUGE:
A pressure gauge is used to measure the pressure of the steam inside the steam boiler. It is fixed in
front of the steam boiler. The pressure gauges generally used are Bounden type.
A Bounden type pressure gauge, in its simplest form consists of an elliptical elastic tube ABC that bent into
an arc of a circle as shown in the figure. This bent up tube is called Bounden’s tube. One end of the tube gauge
is fixed and connected to the sector through a link. Since the tube is encased in a circular cumene therefore it
tends to become circular instead of straight. There is a pointer at which moves over a calibrated scale, which
directly gives the pressure gauge.
WATER LEVEL INDICATOR:
It is an important fitting, which indicates the water level inside the boiler. It is a safety device upon
which the correct working of the boiler depends. This fitting may be seen in front of the boiler and are generally
two in number.
A water level indicator is mostly employed in the steam boiler. It consists of three cocks and a glass tube in
steam cock C₁ keeps the glass in connection with the space of steam. Water cock C₂ puts the glass tube in
connection with the water in the boiler. Drain cock C₃ is used
at frequent intervals to as certain that the steam and water cocks are clear.
For the power functioning of the water-level indicator the steam and water cocks are opened and the drain
cock is closed.
SPRING LOADED SAFETY VALVE:
A spring-loaded safety valve is mainly used for locomotive and marine boilers. It is loaded with spring
instead of weights. The spring is made up of round or square spring steel rod in helical form. The spring may
be in tension or compression as the steam pressure acts along the axis of the spring. In actual practice, the
spring placed in compression.
A ram’s bottom spring loaded safety valve is shown in the above fig. It is usually fitted to locomotive. It
consists of a cast iron body connected to the top of a boiler. It has two separate valves of the same size. These
valves have their setting in the upper end of the two hollow valve chests. These valve chests are united by a
bridge and a base. The base is bolted to a mounting block on the top of a boiler over the fine box. The valves
are held down by means of a spring and a lever. By pulling or raising the lever the pressure from each valve
can be released.
FUSIBLE PLUG:
Fusible plug consists of a hollow gun metal body screwed into the gun metal body by tightening the
hexagonal flange formed into it. There is another solid plug yet which made up of copper with conical top and
rounded bottom. Fusible metal holds this conical copper plug and gun metal plug together due to depressions
provided at the mating surface.
Function of the fusible plug is to protect the fine box crown plate on the fine tube from burning when the level
of water in the water shell falls at normally low and the fine tube, or the crown plate normally submerged in
the water gets exposed to steam space which may not be able to keep it cool.
Conclusion:
