Engineering & Technical Info

If you’re looking for a cavitation chart, the one usually found in control valve catalogs, forget it! The chart is outdated, simplistic and, in most cases, highly inaccurate. Therefore, we no longer publish or subscribe to the data represented. We offer a simple definition that will assist you in understanding this phenomenon.

Cavitation:
The formation of partial vacuums (bubbles of negative pressure) caused by rapid flow and high pressure differential across a valve seat. These negative bubbles collapse under the force of positive downstream pressure. The energy released by these implosions can result in pitting and wearing of the surfaces.

This is a complex phenomenon that cannot be predicted by looking at only the inlet and outlet pressures of the control valve. Here are the variables that contribute to cavitation.

The pressure differential at which cavitation occurs, DPcav, can be predicted from the equation:

DPcav = Cf2(P1-Pv)

where:
Cf = critical flow factor
P1 = valve inlet pressure, psia
Pv = liquid vapor pressure, psia

P1 is determined from your system data. Pv is determined from the type of liquid and its temperature. The control valve determines Cf and varies with the degree of valve opening. The degree of opening is determined by the function of the valve (e.g., pressure reducing, pressure relief, etc.) and the flow rate.

OCV can take the guesswork out of cavitation. The easiest way to predict if your control valve will cavitate is to let us do the calculation for you. Simply fax or e-mail the data listed below. Our engineering team will return a graphical cavitation analysis, and, if cavitation is a possibility, OCV can offer solutions to prevent it.

TYPE OF VALVE:
(e.g., pressure reducing, pressure relief, pump control, etc.)
(or valve function)

MODEL NUMBER:
(if known or we will provide)

SIZE OF VALVE:

FLOW RANGE:
(minimum to maximum)

VALVE INLET PRESSURE:
(including variations, if any, with flow rate)

VALVE OUTLET PRESSURE:
(including variations, if any, with flow rate)

LIQUID BEING HANDLED:

LIQUID TEMPERATURE:

LIQUID VAPOR PRESSURE AT STATED TEMPERATURE:
(if other than water)