Single or double piston effect ball valve against type of fluid

[MaxCarb]

What kind of seat design is the best for a fluid like oil? Single or double piston effect?

Thanks in advance

 

[gerhardl]

Please check forum policies faq731-376.

Afraid you have to specify to get a sensible answer.
(What car is best to use on a road? )

 

[svi]

The question above relates to a ball valve design using a DPE (Double piston effect) seats, both ends. API 6D requires the body cavity to be provided with means of relief for locked in liquid.

I have an identical question,

I wish to ask a question on a NPS 18 ASME Class 600 ball valve with both ends with DPE seats.

Is there any test for a valve cavity pressure simulation. API 6D requires valves with DPE seats to have relieving device installed. However is not clear whether it is needed in all cases. The stream is H2S laden and the owner is unwilling to have the cavity relieve to the open. Can understand the concern, but need to see the likely relief, it may be comparable to the fugitive emmision allowable.

What will be a likley condition that may cause a seat damage to a DPE seat. The likely pressure increase in the cavity cannot be more than the system pressure, except where there is locked-in liquid that completly fills the cavity and the liquid takes a temperature and consequent voume increase. This volume increase is what needs to be relieved. The cavity volume is itself small and consequenlty the volume that is needed to be relieved is also small, so as to bring the cavity pressure from exceeding the seat damaging pressure. This relieving volume being so small. I am just thinking that what ever leak past the seat that had crept into the cavity, can it not happen the same way, to relieve this miniscule volume of liquid past a DPE seat?

Has anyone in here come across any tests to simulate a locked-in liquid in the cavity to see what really happens in case a cavity is presssurised. The cavity pressurization has to be effected by temperature increase rather than by pressure increase to the cavity by a pressure pump. This is so because, the moment the small amount of the liquid that is locked in is let off, the pressure will dip. Moreover, if there is a presence of a small amount of vapour of air in the cavity, the cavity will not see a large pressure increase.

The stream that I have is primarily gas with entrained well fluids of hydrocarbon and water. The temperatures are the middle east ambient.

 

[LittleInch]

There is no real difference to the calcs you do to see if you need a thermal relief valve on shut in piping. Pure liquids, especially hydrocarbons usually do, two phase or gas often doesn't, but if you have volatile substance you might, plus depends on start and end temperature and if you have a fire case or not. You might need a valve relief connected to your closed drain line.

Unless the valve specifically allows cavity relief at some pressure then you can't rely on it and could significantly damage your valve, especially the stem seals.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[svi]

The DPE seats are formed by Elastomeric elements, which in a fire case, may not remain and provide the seal to have the DPE. On Volatile substances, it may condense to liquid phase and fill the void, but then does it not reduce in volume from the condensation. Is there any evidense (either by a test or operation) that a DPE seat can actually cause a stem seal damage and leak.