Certain fittings are necessary on a boiler to ensure
its safe operation. They are usually referred to as boiler mountings. The mountings usually found on a boiler are:
>Safety valves.
These are mounted in pairs to protect the boiler against
overpressure. Once the valve lifting pressure is set in the presence of a
Surveyor it is locked and cannot be changed. The valve is arranged to open
automatically at the pre-set blow-off pressure.
>Main steam stop valve.
This valve is fitted in the main steam supply line
and is usually of the non-return type.
>Auxiliary steam stop valve.
This is a smaller valve fitted in the auxiliary
steam supply line, and is usually of the non-return type.
>Feed check or control valve.
A pair of
valves are fitted: one is the main valve, the other the auxiliary or standby.
They are non-return valves and must give an indication of their open and closed
position.
>Water level gauge.
Water level gauges or 'gauge glasses' are fitted in
pairs, at opposite ends of the boiler. The construction of the level gauge
depends upon the boiler pressure.
>Pressure gauge connection.
Where necessary on the boiler drum, superheater,
etc., pressure gauges are fitted to provide pressure readings.
>Air release cock.
These are fitted in the headers, boiler drum, etc.,
to release air when filling the boiler or initially raising steam.
>Sampling connection.
A water outlet cock and cooling arrangement is
provided for the sampling and analysis of feed water. A provision may also be
made for injecting water treatment chemicals.
>Blow down valve.
This valve enables water to be blown down or emptied
from the boiler. It may be used when partially or completely emptying the
boiler.
>Scum valve.
A shallow dish positioned at the normal water level
is connected to the scum valve. This enables the blowing down or removal of
scum and impurities from the water surface.
>Whistle stop valve.
This is a small bore non-return valve which supplies
the whistle with steam straight from the boiler drum.
Boiler mountings (water-tube boilers)
Watertube boilers, because of their smaller water
content in relation to their steam raising capacity, require certain additional
mountings:
>Automatic feed water regulator.
Fitted
in the feed line prior to the main check valve, this device is essential to
ensure the correct water level in.the boiler during all load conditions.
Boilers with a high evaporation rate will use a multiple-element feed water
control system.
>Low level alarm.
A device to provide audible warning of low water
level conditions.
>Superheater circulating valves.
Acting also as air vents, these fittings ensure a
flow of steam when initially warming through and raising steam in the boiler.
>Sootblowers,
Operated by steam or compressed air, they act to
blow away soot and the products of combustion from the tube surfaces. Several
are fitted in strategic places. The soot blower lance is inserted, soot is
blown and the lance is withdrawn.
Ref: introduction to marine engineering by D A Talyor
Ref: introduction to marine engineering by D A Talyor