Cavitation is the phenomenon where small and largely empty cavities are generated in a fluid, which expand to large size and then rapidly collapse, producing a sharp sound. Cavitation occurs in pumps, propellers and at restrictions in a flowing liquid.
Suction cavitation occurs when the pump suction is under a low pressure/high vacuum condition where the liquid turns into a vapor at the eye of the pump impeller. This vapor is carried over to the discharge side of the pump where it no longer sees vacuum and is compressed back into a liquid by the discharge pressure.
Damage caused by suction cavitation:
This imploding action occurs violently and attacks the face of the impeller. An impeller that has been operating under a suction cavitation condition has large chunks of material removed from its face causing premature failure of the pump.
Discharge cavitation occurs when the pump discharge pressure is extremely high. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. As the liquid flows around the impeller it must pass through the small clearance between the impeller and the pump at extremely high velocity.
Damage caused by discharge cavitation:
This velocity causes a vacuum to develop (similar to what occurs in a venturi) which turns the liquid into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump . In addition due to the high pressure condition premature failure of the pump mechanical seal and bearings can be expected. Under extreme conditions this can break the impeller shaft.
Discharge cavitation is believed to be the cause of the cracking of joints
Check your system for these conditions which may contribute to, or directly cause, cavitation:
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Inadequate inlet line size |
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Insufficient inlet flow or excessive suction
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Excessive inlet line length
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Rigid inlet plumbing |
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Too many elbows and/or fittings |
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Excessive temperature build-up or pumped fluid |
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Air leak in inlet plumbing |
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Agitation in supply reservoir |
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Inadequate increase of inlet flow for fluids of greater specific gravity |
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Inadequate increase of inlet flow for higher temperature fluids |
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Clogged inlet filters |
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