Blow off Cock – Construction and Working [Complete Guide]

Blow off Cock is a mounting of a boiler. As we can understand from its name, it is used to blow off the water from the boiler and empty the boiler.
It is also used to discharge mud and other sediments deposited in the bottom-most part of the water space in the boiler while the boiler is in operation. It is used to remove periodically the sediments collected at the bottom of the boiler.
To discharge mud and other sediments deposited in the bottom-most part of the water space in the boiler, while the boiler is in operation.
Blow off Cock is a mounting of a boiler

Location:

It is located at the bottom left of the boiler.
When it is opened the mud and sediments are taken away by the water rushing out of the boiler as the pressure of water rushing out of the boiler is very high due to high volume of water.
Sediment removal is carried out by discharging a portion of the water by opening the blow off cock.
The water leaving the boiler which is under pressure rushes out carrying the sediments with it when the blow off cock is opened.

Blow Off Cock

Construction of Blow Off Cock:

It is fitted in the bottom of the boiler shell either directly or through the short branch of pipe at the lowest part of the water space.
A blow off cock generally consists of a conical,hollow, gun-metal plug type valve that fits accurately into a corresponding hole in the casing.
This plug valve has two faces, one face is fully solid and another face has a hole through which the water can flow. This plunk valve shank projects out of the stuffing box gland. The stuffing box is provided to prevent the leakage of water at the shank.The gland can be tightened with the nuts provided under the plug to force it off its seat is jammed.

A guard is present over the spindle which prevents removing of handle unless the cock is connected to the boiler by one of the flanges. The flow off cock is connected to the boiler by one flange and the other flange is connected to the pipe carrying the blow off water out of the boiler house.

Working of Blow Off Cock:

The plug valve has two faces, one of which is fully solid and another face has rectangular hole. By default when the boiler is in operation, the solid face of the plug valve is facing towards the hole of the casing and the water in the casing strikes the solid face of plug valve and hence water is stopped from going out of the boiler.

When the boiler water has to be drained off or the sediments and mud in the boiler has to be removed, the hand wheel of the blow off cock is rotated. As the hand wheel is rotated the face of plug valve with hole faces towards the casing whole containing water and the water starts flowing out of the boiler through blow off cock.

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