Hi
I currently have a PSV on a steam ejector suction chamber which has a set pressure above the test pressure.
Design Pressure = 15 PSIG
Test Pressure = 22.5 PSIG
PSV set pressure = 25 PSIG
The PSV is protecting the suction chamber of the ejector. The ejector has a discharge valve. If this is closed during operation, or not opened during start-up then the suction chamber (which will usually be at vacuum condition) could see the full motive steam pressure of 399 PSI. The motive steam piping is all rated, and the surface condenser from which steam is being pulled from has its own overpressure protection.
HEI standard for steam jet vacuum systems says that the set pressure should be 15 PSIG (or no higher than design pressure).
The vendor literature also says the set pressure should be 15 PSIG (or no higher than design pressure). I've been in touch with vendor however cannot come to a resolution of why this PSV was set this high. (It was done back in 1982, however the HEI standards haven't changed regarding PSV set pressure. The vendor is now saying that the PSV set pressure can be higher than set pressure but no higher than the test pressure which is still not OK at my PSV is set above the test pressure.
I'm recommending reducing the set pressure to 15 PSIG and checking PSV capacity is OK.(which it isn't!!) However I am really interested in why this set pressure was chosen in the first place. The ejector mechanical drawings and documentation specifically say hydrotest pressure 22.5 PSIG, and PSV set pressure 25PSIG so I cant see this being a mistake as someone would have surely seen it. (Am I missing something or misinterpreting the HEI standard?)
Anyone clued up on steam ejector PSVs???
Appreciate any help