Pressure Safety Valves (PSV)

The ratio of specific heats (at constant pressure over constant volume) is used in the equations for selecting a pressure relief valve.

I hope that these are just general questions and you are not actually trying to select a valve - because this is a specialty area and should be left for someone with experience as there are a lot of factors to consider - and the consequences of selecting a wrong relief valve are great.

Overpressure factor is typically 10% for normal relief and 21% for a fire case.

Cp/Cv for water is 1.33. It varies for different materials.

Water vapor and steam are essentially the same thing.

Hi every body

Let get API-520 and API-521 for more clear,

The over pressure is considered based on case by case basic (i.e. fire case, gereral power failure case, control valve wide open case...)

So, pls find out the standard above

as rightly above told it is 10% for cases except for fire & 21% for fire.also i want to tell u one thing in fire why it is 21%....actually as far i know it is a margin of 10% above 10%....if anybody has a different view can correct me...