Set Pressure < Sizing Pressure <= A x MAWP/Design Pressure. A is according to the effective Code (1.0, 1.1, 1.2, 1.21, etc.).

If Design Pressure is 16 osi and API 650 Code. My first pass would be something like:
Normal vent set pressure = 4 osi.
Normal vent sizing pressure = 8 osi.
Emergency vent set pressure = 8 osi.
Emergency vent sizing pressure = 16 osi.

Why? The old rule of thumb is the sizing pressure has to be about twice the set pressure for the pallet to be fully open (it was fully open before that, but this made it easy, and it gave some conservatism).

Good Luck,
Latexman
Pats' Pub's Proprietor

Is osi the abbreviation for ounce per square inch?

Yes. The example works for any units.

Good Luck,
Latexman
Pats' Pub's Proprietor

You can set the PVRV at up to a max of say 75-80% of tank design pressure. That will give you the remaining 20-25% for accumulation to reach full lift.