cavity pressure relieve for a 2" floater ball valve

[Mous1747]

even thought the seats are self-relieving but the customer is requesting a direct discharge relieve port in the body cavity that release to the upstream, i never seen this. how this design will look like ? where the tap will be located and how to release to upstream?

 

[zdas04]

DON'T DO IT. A floating ball valve is intended to FLOAT. It is not fixed and requires differential pressure to push the ball off the seat into the downstream flange. Consequently the body cavity is always at the same pressure as the upstream pipe. If you put a PSV on the body cavity to relieve back to the upstream (at the same pressure) the result is zero flow. What a waste of time, money, and effort

On the other hand. A trunnion ball valve has spring loaded seats and the ball is held rigidly against lateral movement by the trunnion bearings. Putting a PSV in the body bleed on a trunnion ball valve can be a good idea (thermal relief if nothing else), but going back to the upstream side is a bit iffy (remember, the PSV you are likely considering is a non-pilot valve that senses the difference between inlet pressure and exhaust pressure so changes in upstream pressure change the "setpoint").

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Ehzin]

I would question them on their intent to understand why they would want this. There could be at least some logic on their request although probably not much.

I may be getting the wording they used wrong but they could be implying a port drilled directly into one side of the ball itself. This could allow for isolation in one direction then function to some degree as a restriction orifice to limit flow in the other direction. Not saying this would be the recommended way to address what they may want but there could be some reasoning to what they're requesting. Find out what they're actually looking for regarding operation/performance and then work on a solution from there.

Thanks,
Ehzin

 

[zdas04]

There are floating ball valve made for tanks that do have a substantial hole drilled in the upstream side of the ball. The reason for this is when the valve is shut and the fluid in the body cavity freezes (because it is a limited volume) it will either split the casing or separate it. The hole keeps the cavity exposed to the (heated) fluid in the tank. But no one calls these holes relief devices.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist