Construction and Working [Video Lesson]

Construction [Video Lesson] Watch this video to understand the basic construction and operation of a marine boiler safety valve –

 

The function of a safety valve is to prevent excessive pressure from building up in a steam boiler, thus guarding the boiler against possible explosions. The safety v/v is set at a pressure not exceeding 3% of the approved boiler working pressure.

 

When the boiler pressure exceeds the set value, the excess steam is released through a waste steam pipe. The set pressure of a safety valve is adjusted by varying the spring tension. The valve lift is designed such that a sufficient amount of steam is released to reduce the excess pressure.

 

The valve disc has a lip on the periphery to provide additional lift. The additional lift counteracts the increase in spring load due to compression. Depending on the lift, the safety valves are classified as high lift and improved high lift valves.

 

The pressure drop after the release of excess pressure is called blowdown. The lifted safety valve should be reseated promptly to control the loss of usable steam. A blowdown ring is screwed onto the valve body and it encircles the valve seat. This determines the amount of blowdown and the prompt reseating of the valve.

 

The vertical position of the ring can be adjusted through a plug hole, while the valve is under pressure.

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