In actuality, the maximum liquid flow through the valve can never exceed a choked flow limit, and at this point flow will increase no further, no matter how low the P 2 pressure is reduced.Ī similar phenomenon occurs with valves in gas service. In reality, the maximum fl ow will be limited due to choked flow conditions.

In an ideal world, fl ow rate through a valve rises as the pressure drop across the valve increases. The “Ideal” line in figure 1 illustrates this point, showing how liquid flow rises linearly when charted against the square root of the differential pressure across the valve divided by specific gravity.įigure 1.

If the inlet pressure (P 1) and valve flow area are fixed, the flow through a valve will normally rise as the downstream pressure (P 2) is reduced. It also explains when choked flow conditions are damaging and how this damage can be reduced or avoided. This article describes the phenomenon of choked flow and shows why it occurs and how it can be predicted. Although choked flow is not always the cause of these conditions, it may indicate when they occur. The term is usually associated with destructive process conditions that can damage valve internals or expose operators to noise levels well above OSHA limits. Choked flow is a poorly understood phenomenon that can affect control valve sizing, along with trim and material specification.Ĭhoked flow in control valves is a subject of serious concern for industrial users.

Cavitation airflow systems