ABSTRACT

The fluid resistances discussed so far are all intended to be essentially constant in numerical value. Many fluid systems require adjustable resistances, and often these take the form of some kind of valve. Valves are of many different types and perform various functions in fluid systems. We are here considering, not the "on-off' type of valve, which is either completely open or completely shut, but rather those valves used to smoothly modulate the flow rate. Such valves are used in many manual or automatic fluid control systems. The vast majority of valves have a square-root type of pressure/flow relation, such as Eq. (4-37), and usually require experimental calibration if we want a reasonably accurate flow model. The flow modulation is achieved by somehow varying the "orifice" area A 0 • A complete calibration would thus give a family of flow rate versus pressure drop curves, one for each flow area.