PSV Dischrage Pipe

[Mrepp]

Is it a hard and fast rule that the PSV discharge pipe be at least as large as the PSV discharge connection? I am looking at an as-built pump skid with a blocked discharge PSV -1"x1" - with a 3/4" connection to a 2" line back to the tank. Don't have API 520 with me and no discussion I have searched through speaks directly to this. The company standards are to follow API 520 installation guidelines.

 

[Homayun]

Merpp,

API 520 says that the following:
" With balanced PSV's, higher manifold pressure may be used. The balanced valves function independently of the back pressure; however their capacity begins to decrease when the back pressure exceeds 30-50% of the PSV set pressure."

I usually try to limit the back pressure at the discharge piping to 30%. But if you are looking into an existing system, you may allow 50%.

Hope this has been helpful.

Regards

 

[ProPiper]

Homayun, why you presume this is a balanced typ PSV?


Merpp, I guess this is a reciprocating pump case, a conventional type PSV is to protect discharge piping from oper pressure. 10% is the the from API 520. But I wouldn't do any calculation if we are tlking a metering pump, I am sure 3/4" will be OK.

 

[ProPiper]

Merpp, some typos there. See the corrected text below:

I guess this is a reciprocating pump case, a conventional type PSV is to protect discharge piping from over pressure. 10% is the the rule from API 520. But I wouldn't do any calculation if we are talking a metering pump, I am sure 3/4" will be OK.