IWA Publishing

Dealing with Cavitation in Control Valves

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Courtesy of IWA Publishing

Cavitation consists of rapid vaporization and condensation within a liquid. When local pressure falls to vapor pressure (approximately 0.25 psi / 0.018 bar absolute for cold water), vapor bubbles are formed and when these bubbles travel to an area of higher pressure, the bubbles collapse with phenomenal force and great localized stress. It is the violent collapse of these vapor bubbles near valve components or downstream piping surfaces, which cause cavitation damage and subsequent performance degradation. Typically, the reason for low pressure is that the pressure drop across a control valve has created very high velocity in the seat area and corresponding low pressure because potential (pressure) energy is reduced to compensate for the increase in kinetic energy.  This principle, known as Bernoulli’s Principle was named after the mathematician Daniel Bernoulli and was first published in 1798 in his book, Hydrodynamica.  The principle can be applied to various types of fluid flow and simply states that when there is an increase in the velocity of fluids then it must be accompanied by a decrease in the fluid’s pressure, the total energy associated with the flow must remain constant.  And as summarized above, in scenarios where the pressure drops to vapour pressure, cavitation will occur.

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