Trunnion Ball Valves in Vacuum Service
Trunnion Ball Valves in Vacuum Service
(OP)
Can a standard, soft seated trunnion ball valve be used in a vacuum service? I hear that these types of valves often have trouble sealing bubble tight at relatively low pressures, say 80 PSI, and if true it seems like vacuum service would only compound the problem.
The other side of this would be while the upstream seat that normally seals with positive pressure might be compromised in a vacuum, it seems that the downstream seat would be helped (vacuum would pull it into the ball making an even tighter seal).
Just curious if anyone has some real world experience, or knows of manufacturers who have been successful in the past.
The other side of this would be while the upstream seat that normally seals with positive pressure might be compromised in a vacuum, it seems that the downstream seat would be helped (vacuum would pull it into the ball making an even tighter seal).
Just curious if anyone has some real world experience, or knows of manufacturers who have been successful in the past.





RE: Trunnion Ball Valves in Vacuum Service
On trunion ball valves, the only seating mechinism is the springs that push the seat into the ball. I've used them in very low dP service and vacuum service and I can't point to a valve that has a better chance of long-term success in vacuum service.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The Plural of "anecdote" is not "data"
RE: Trunnion Ball Valves in Vacuum Service
I still have the concern about sealing bubble tight at low pressures (less than 80 PSI). Once you get above 80 PSI, the seat presses so hard into the ball it will almost always make a tight seal unless it is seriously damaged, but below that it may be tough to get a perfect seal, and you will have a slow leak across the seat. My concern is a vacuum will only make this worse by couteracting to a degree even the small force of the compressed spring.
RE: Trunnion Ball Valves in Vacuum Service
You have to keep in mind that the dP on a trunion ball valve is actually the difference between the upstream piping and the trapped gas within the ball, and between the trapped gas and the downstream piping. One is helping the springs and the other is opposing the springs. The net can be pretty small.
On the other hand I've had situations where I had a high pressure on both sides of the valve with the body cavity vented. This should yeild maximum dP across both seats, and in that case the gas required to start the ball turning was about the same as any other time.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The Plural of "anecdote" is not "data"