Choked Flow in Control Valve Applications

Choked flow is also known as critical flow in control valve applications. It occurs when an increase in pressure drop across the valve no longer creates an increase in flow.  In liquid applications, the capacity of the control valve is severely limited if the pressure conditions for the liquid are low enough to cause flashing and cavitation.

For gases and vapours, the capacity is limited if the velocity reaches the sonic velocity (as referred to as MACH 1). To understand how these conditions occur, we look at the normal pressure to flow relationship for a control valve and see when choked or critical flow conditions occur. The basic relationship between flow and pressure in a control valve is given by:

Read more »