For the most comprehensive procedure in sizing pressure reducing valves, it is best to use our ValveMaster software or the Performance Charts in the Engineering Section of the OCV catalog. In the absence of these, the following procedure will get you where you need to be, and enable you to avoid the most common error in sizing PRVís: an oversized valve.
The following procedure takes both factors (flow rate/pressure drop) into account through the use of the flow coefficient, or Cv. The theory is simple: for best results, a PRV should be sized to operate between 10% and 90% of its capacity, or in other words, between 10% and 90% of its wide open Cv. It is a four-step procedure: