How do I find the PSI

I suggest you have a chat with your client and inform him that he should look elsewhere for the information you are not qualified to provide.

No. mareng is right.

Take two weeks off and then quit.

insufficient data; depends on the temperature

"I don't know" is a perfectly acceptable answer.
Vast ammounts of time and resources are wasted by people who, for reasons best known to themselves, refuse to give the above answer.
Most of them are 'salesmen' or kids working in supermarkets who lead you round and round searching for the soy sauce when you probably have a better idea of it's location than they do...Oh and don't start me on "financial advisors".
Del

Despite all the comments by the so called helpful members

1. The basic concept stands, if you don't really understand and nor does your client, do not attempt it. At the pressure you mention, it is dangerous

2. But just for your knowledge (not for use till you really understand the complexity), the pressure is dependent on the temperature also. Just for a common sense, you do not expect a pipe that is OK for 10 bar water pressure to withstand 10 bar of superheated steam (as the temperature riss, the mechanical properties fall). So the classes are not exactly the pressure ratings in psi (as is mistakenly assumed) but it denotes a complex pressure-temperature withstand capacity. An example is here. You may also note that it is material dependent.

For example at 400⁰F, Carbon steel flange is rated for 1270PSI but 316 is 1030 and 316L is only 824 whereas CrMo steel will have 1400PSI withstand capacity.

This brief explanation may be sufficient, but it is just for enlightenment and not for use unless at least one of the parties really understands about it. Afterall 2800PSI can easily destroy an area including its inhabitants (assuming it is non-toxic/explosive fluid)

If you are not an Engineer then why is your Client dumb enough to ask you?

..and why do you need to reply? Learn to say "no" by politely asking your client to revert this question/s to an engineer.

Listen the valve sees the pressure in a static mode.... i.e. turned off. The only pressure the valve will see in a dynamic mode (open) is Δ P.

Only when the flow is great and Δ P across the valve is greater than the rating.......so be very careful......if you bring and accountant or sales in..... he may give it his blessing.

Seriously stop. Let someone who is familiar with this type of applications.

p911