Need 15psi soft seal pressure relief valve
Need 15psi soft seal pressure relief valve
(OP)
I need a 1" 15psi soft seal pressure relief valve.
We are building a high voltage test chamber that will be filled with sulfur hexafluoride (SF6) to prevent arching. The plan for the chamber is to pump it out to around 10^-3 torr or lower (aka higher vacuum) then to fill it with SF6 up to 1 atm (gauge pressure not absolute). My understanding is that if the pressure is kept below 15 psi above atmospheric pressure we do not have to certify it as a pressure vessel so that's the reason we need the relief valve. We bought a kunkle valve from mcmaster carr (http://www.mcmaster.com/#6017t13/=7qe10e) and when we tested it we realized it did not hold pressure and started weeping well below 15psi. So I need help in finding a soft sealing (because it has to hold vacuum) 15psi pop safety valve. It can't start weeping much before 14.7 psi.
Thanks,
Steve
We are building a high voltage test chamber that will be filled with sulfur hexafluoride (SF6) to prevent arching. The plan for the chamber is to pump it out to around 10^-3 torr or lower (aka higher vacuum) then to fill it with SF6 up to 1 atm (gauge pressure not absolute). My understanding is that if the pressure is kept below 15 psi above atmospheric pressure we do not have to certify it as a pressure vessel so that's the reason we need the relief valve. We bought a kunkle valve from mcmaster carr (http://www.mcmaster.com/#6017t13/=7qe10e) and when we tested it we realized it did not hold pressure and started weeping well below 15psi. So I need help in finding a soft sealing (because it has to hold vacuum) 15psi pop safety valve. It can't start weeping much before 14.7 psi.
Thanks,
Steve





RE: Need 15psi soft seal pressure relief valve
I forgot to add I am located at Triumf in Vancouver BC, Canada so local or Canadian companies would be preferred.
RE: Need 15psi soft seal pressure relief valve
What model of Kunkle valve have you got?
I haven't dealt this kind of issue, and have question:
Do you need to supply PRV for vacuum too? I though PRV works only for excessive pressure.
regards,
Curtis
RE: Need 15psi soft seal pressure relief valve
You may want to ask this over in forum408: Valve engineering. That's where the valve folks "hang out."
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Need 15psi soft seal pressure relief valve
RE: Need 15psi soft seal pressure relief valve
snd can go up to 13.5 psi w/o popping.
genblr
RE: Need 15psi soft seal pressure relief valve
If you do put a disc under the valve, make SURE you put a proper means of leak detection in there between the disc and relief valve inlet. There are numerous options for what to do there, and which one you choose depends on how frequently it will be attended and how probable leakage through the rupture disc is.
RE: Need 15psi soft seal pressure relief valve
too close for comfort,
even soft seat valves will start weeping at 14 psi and pop at 15.- what's your vacc7um pressure?
genble
RE: Need 15psi soft seal pressure relief valve
I am just looking for a reliable 1" soft seal pop safety valve that will hold a pressure of around 14psi and pop at around 15psi. It's great that your valves work well but it's pretty useless to me if you don't tell me what kind or send me a link.
RE: Need 15psi soft seal pressure relief valve
A relief valve typically simmers (i.e. starts relieving) within 90% of its set pressure unless it is a very special design- in your case that's 13.5 psig. I would imagine a low pressure soft seated valve will probably simmer even lower than 90% of its set pressure. As to inward leakage against vacuum, they're going to leak.
Either be satisfied with slightly lower pressure or trip over the 15 psig magic ASME limit- it's your choice. You can't have your cake and eat it too!
RE: Need 15psi soft seal pressure relief valve
RE: Need 15psi soft seal pressure relief valve
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Need 15psi soft seal pressure relief valve
RE: Need 15psi soft seal pressure relief valve
talk to Alex stocks soft seat valves.
you can buy one really cheap and test.
But why not Get an ASME cert. vessel,
how big is the unit that you want to get around a certification.
if small it should not be that expensive.,
ask around.
Ican not -post any commercials but, seems easy.!!
genblr
RE: Need 15psi soft seal pressure relief valve
He did, posted a link back here. It's what he is supposed to do, according to the posting guidelines.
RE: Need 15psi soft seal pressure relief valve
Even ASME rated relief valves suffer from the same problem.
For your purposes, for a <15 psig "vessel", the ASME B&PV rules do not apply. What you are trying to make is a precision back pressure regulator, not a relief valve per se. Figure the worst case incoming gas flow rate, and design the valve accordingly. Or, if the arc/electrical heating of the gas within the enclosure is a concern, include a blowout panel or burst disc, as others have proposed.
RE: Need 15psi soft seal pressure relief valve
One reason you are struggling is that you probably bought too small a check valve. If you want a closer limit between your flowing and cracking pressure, purchase a check valve that is too large by about a factor of 10, i.e. if you were using a 1/4" pipe size valve, go buy a 1.25" or 1.5" check valve, and you should see the two pressures move closer together. I could give you reasons for this, but it's pretty simple math.
RE: Need 15psi soft seal pressure relief valve
The problem is it doesn't hold any pressure. When we left the valve pressurized overnight it had 0 psi of pressure. If it held even 11psi that would be acceptable although not ideal.
I did design a very simple valve using an O ring and a spring but it would cost far too much make it and the head engineer wouldn't even accept it because it's not certified. The valve we bought cost $155. For a custom valve (even the very simple one I designed) the machining would take at least 2 hours billed at $89/hour which would be more expensive without even taking material cost into account.
RE: Need 15psi soft seal pressure relief valve
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Need 15psi soft seal pressure relief valve
What material is the seal? Is it an o-ring, and if so, can you source a butyl rubber replacement. Butyl is much less permeable than the (probably) nitrile rubber that the seal is made from. Also, check if any dirt/debris is on the seal. Finally, get some silicone grease and smear on the seal. Last - are you SURE the valve, and not some other part of your system, is the leak path?