Liquids Flow Rate

Conventional Valve, Balanced-Bellows Valve, or Pilot-Operated Valve

The corresponding equations for liquid flow are the following:

cal-13-4

Capacity correction factor, K,, due to viscosity. (Reprinted with permission from
Capacity correction factor, K,, due to viscosity.

Back-pressure correction factors for 25% overpressure on balanced-bellows pressure relief valves in liquid service. {Reprinted with permission from API 520.)

Note that a preliminary orifice size must be determined in order to calculate Reynolds number. If the viscosity correction is significant, it may be necessary to iterate to get a final size.