Dear All members,
I have an issue with the liquid relief PSV.
The PSV are installed on pump discharge line for blocked outlet case and they are required a certification on capacity. PSVs type are conventional and also balance bellow.
Recently i got vendor quotation with two following issues:
1. PSV set pressure is 10barg. Pump discharge pressure is 8.5barg. Then Vendor has informed that for liquid relief PSV, they require 20% of set pressure for blowdown pressure. it means they ask us to change Operating pressure to 8barg. I cannot reduce operating pressure, and also cannot increase design pressure because this is an existing system. What is the solution in this case?
2. I have two vendors, one quotes API orifice size which gave less rated flowrate. Another one quotes ASME Orifice size which gave a very big rated flow. From process point of view, boths are fine. however, the Vendor who quotes ASME orifice explained us that because PSV is certified capacity, therefore they need to follow ASME VIII code. All projects that i did for this Client was API orifice, therefore the Client is not confident to go with ASME orifice (this vendor quotes a cheaper price)
I am abit confuse about API and ASME orifice. (i have read API520 and ASME but i still cant get the answer).
Do we have to follow ASME VIII all the time for the liquid PSV iwth certified capacity requirement? if yes, why some vendor still quote PSVs under API orifice type not ASME?
If anyone can explain me clearly about this.
I apprecite any help.
Thank you very much.