I guess my question is misleading. I've seen PSV and ERV specification require no aluminum or copper parts. I understand aluminum can not stand for high temperature. But I am not sure under what applications, copper is not allowed on pressure relief devices. Please advise.
Some lube oils contain sulfur, both from the constituency of the base crude stock, and as an additive for anti-wear purposes, so brass wouldn't be indicated for that service either.
Obviously, carol2005, the specification you were reading was dealing with either a pressure issue, or a chemical issue where brass would not suffice for the service.
Do you have any insight as to what type of service the PSV's in question were for?
I used to use PSV's on seawater service, and they were 100% bronze for obvious reasons.
Here's my take on the Copper part of the question.
Copper being so maleable, a SV made of it would easily distort from piping loads, vibration and the like. The body could possibly creep due to the disc closing spring forces. The corrosion patina could interfere with moving parts and jam up the works, any heat would reduce ultimate strength and further exacerbate distortion issues.
If the body distorted, alignment would be affected and the SV would most likely pass/leak. If the disc was copper too, then the metal to metal seat would probably be chewed out in no time flat as well.
Cheers
Rob
BUT, add some alloying elements to copper and you get a much hardier material aka brass / bronze etc...
