safety valve unstable operation terms

     

Unstable Operation of safety valve

Unstable operation often results from misadjustment.

The following are the state of unstable operation and its remedy.

 Chattering

This is a rapid reciprocating variation in valve lift during which the disc repeatedly

contacts the seat. It is because popping power is weak. In this case, bring up

the lower ring (closer to the bottom face of the disc).

Hunting

This is the state where the disc repeats violent vertical motion during operation as if

it beats the seat violently. This is often caused when there is much flow restriction in the pipings connected with inlet and discharge side of the safety valve or when blowdown period is excessively too short. In this case, open the adjusting cook or throttle valve or bring down the upper ring to increase blowdown. lf hunting is not ceased despite the above adjustment, rechecking of the piping is necessary.

Fluttering

This is an abnormal reciprocating motion in valve lift during which the disc does

not contact the seat.

This is caused by the unbalance of the relative part against valve lifting power.

In this case, bring down the upper ring to increase the valve lifting power.

with canvas or the like to shut off the air.