Pressure Relief Valve Chattering
Pressure Relief Valve Chattering
(OP)
Can anyone offer an opinion based on experience or physics which support the position that there is more tendency for SRV in Liquid to service to Chatter than SRV in Compressible Fluid Service? Thank you.
JAC





RE: Pressure Relief Valve Chattering
RE: Pressure Relief Valve Chattering
Best regards
Morten
RE: Pressure Relief Valve Chattering
Subsequently, the pressure rebuids in the vessel and the valve starts to open, and before it is far from the seat, it closes due to the rapid decrease in pressure. Ad infinitum.
Paul Ostand
www.ostand.com
RE: Pressure Relief Valve Chattering
I gave i shot but im not sure thats why.
Best regards
Morten
RE: Pressure Relief Valve Chattering
A SRV for gas is most often (or should be) especially designed for gas with a special designed (and sometimes adjustable) reaction ring. This reaction ring (formed as an extra 'skirt') has the purpose of gathering and leading the gas flow to open the SRV smooth and fully, and avoid chattering.
The reason for the skirt is 'mass flow' necessary to keep the disc lifted, and as such, I believe, partly answer to your question.
But answer for physics backed by correct design: Properly designed SRVs (different designs for incompressible and compressibel fluid) should at least be somwhat equal compared to shattering tendency.
Answers for other than physics: As shattering occurs when operating pressure is reoccuringly too near lifting pressure or just above lifting pressure and repeatedly relieved by small outlet amounts, this is either caused by selecting a too large valve or wrongly selected or adjusted set pressure compared to process operating pressure. Human fault presumed equal for both types of fluid!
RE: Pressure Relief Valve Chattering
API 520 states that 3% max dP in the inlet should be designed for. It dosnt state this clearly - but I was under the impression that this was in order to avoid chattering. Is this not the case?
Best regards
Morten
RE: Pressure Relief Valve Chattering
But my concern is really whether liquids have more propensity to chatter than gases given the same inlet piping configuration.
Thanks,
AC
JAC
RE: Pressure Relief Valve Chattering
Somebody has written about a reaction ring. I think it's one of the factors which has influence in chattering (or fluttering). It deals with the concept of "blowdown" in a PSV. Depend on how you adjest the blowdown ring you can modify the pressure for close in two ways: more early o more late.
RE: Pressure Relief Valve Chattering
The geometry would presumably be a little different to do the same thing for a gas valve.
Mike Halloran
Pembroke Pines, FL, USA
RE: Pressure Relief Valve Chattering
I have two identical SRV's on two separate, but identical, piping systems and they're set to pop at the same pressure. The pressure profiles in my two piping systems are identical. In fact, everything about the setup is identical between the two except that one of the fluids is completely liquid, and the other completely gaseous. No two-phase flows.
Okay, so we ramp the fluid pressures up to the set point and the valves begin to open. As the liquid valve opens, a small amount of liquid comes out, the pressure drops quickly, and the valve closes. However, the gas should be a bit different. As its valve opens, a small amount of gas begins to leave the valve, but as it is a gas and enjoys its space, it begins to expand when it encounters the lower external pressures. It seems that more volume has to go through the valve, so it would tend to stay open a bit longer than the similar liquid valve. Since the period that the valve is open is longer, the chatter appears to have a lower frequency.
Your job is to see the angles I missed in my thinking. One possible angle is that the local pressure of the gas at the disc face drops quickly due to the expansion through the valve and the disc closes, only to encounter the pressure rebound caused by the system pressure, which quickly opens the valve again. I suspect there are a lot of little factors that I missed that would be helpful to know. Maybe we'll all come out of this learning a bit more on the way to figuring out what's going on 4 NoSoup4U.
Now, I have to ask: we are talking about chatter and not simmer here, right?
RE: Pressure Relief Valve Chattering
JAC
RE: Pressure Relief Valve Chattering
One more difficult issue is to make sure that the poppet will seal again when the pressure drops after a minimum specified pressure difference below the crack point. I have seen bad designed safety valves that seal back after cracking in a pressure lower than 80% of the crack pressure.
RE: Pressure Relief Valve Chattering
RE: Pressure Relief Valve Chattering
Size your liquid PRV carefully
RE: Pressure Relief Valve Chattering
JAC
RE: Pressure Relief Valve Chattering