Valve size often is described by the nominal size of the end connections, but a more important measure is the flow that the valve can provide. And determining flow through a valve can be simple. This technical bulletin shows how flow can be estimated well enough to select a valve size—easily, and without complicated calculations. Included are the principles of flow calculations, some basic formulas, and the effects of specific gravity and temperature. Also given are six simple graphs for estimating the flow of water or air through valves and other components and examples of how to use them.

Swagelok-2002-Valve-Sizing-Technical-Bulletin.pdf

Swagelok (2002) Valve Sizing Technical Bulletin