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Cavity relief for Trunnion Ball Valve

Cavity relief for Trunnion Ball Valve

Cavity relief for Trunnion Ball Valve

(OP)
My custome has required a Trunnion mounted ball with cavity relief by seat leakage to inside of valve.
Normaly the Trunnion type are self relief sealing but in this case i dont' understood what's mean about cavity relief by seat TO INSIDE OF VALVE !!

RE: Cavity relief for Trunnion Ball Valve

Seats occasionally leak by.  If you overpressure a trunnion boy cavity it will self relieve through the other seat.  A PSV threaded into the body bleed port can prevent the self relieving if you just can't allow any flow all the way across the valve.

Set point is a big issue.  It only takes a couple of psi of over pressure to lift the seat from the back.  If you set the PSV at a couple of psi then it will lift every time you shut the valve.

Tough problem.  You can solve it with a dP control valve that samples upstream and downstream and sends the lower pressure to the static side of a dP PSV which is set to lift when the cavitiy is 2-3 psid higher than the low pressure side of the Trunion.  It sounds complicated, but it is pretty easy.

David

RE: Cavity relief for Trunnion Ball Valve

forget a PSV.  Install a 1/2" tubing check valve with a 10 psi spring.  The valve is yubed from the body bleed tap to a point on the upstream or downstream side of the vale (the low p[ressure sink of cooling side/underground run).

 

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