Cavitation

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Cavitation
A phenomenon which occurs within a moving liquid when
the static pressure at some location falls to or below the vapor
pressure of the liquid.
To prevent cavitation:
NPSHA > NPSHR
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Cavitation
Cavitation
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Cavitation – Impeller
Cavitation can occur at the inlet of the impeller if the suction pressure
falls below the liquid vapor pressure.
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Cavitation - Impeller
Cavitation – Impeller
Large vapor volumes can
cause reduction in head
generation, or loss of prime.
• Bubbles collapsing create
intense pressures and
(10,000 psi) shock waves.
• Intense pressures near metal
surfaces exceed material
strength and fatigue metals.
Large vapor volumes can cause
surging and unstable flows.
• Creates pitted surfaces.
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Cavitation - Impeller
Cavitation
Cavitation is caused by liquid changing into a
vapor and then back into a liquid. The
Formation of partial vacuums in a flowing liquid
as a result of the separation its parts. When
These collapse, pitting or other damage is
Caused on metal surface in contact.
Cavitation is NOT AIR in the PUMP!
There are two forms of cavitation:
• Suction Cavitation, which occurs at the eye of the impeller, (also referred to as
“true cavitation”.
• Discharge Cavitation, which occurs at the tip of the impeller, (also referred to as
recirculation cavitation).
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What Damage Does Discharge Cavitation Cause?
• Break Shafts
• Shortens Bearing Life
• Destroys Impellers and Volutes
• Ruins Mechanical Seals
Total Dynamic Head Too “HIGH”
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What Damage Does Suction Cavitation Cause?
• Shortens Bearing Life
(Increased radial & thrust loads)
• Destroys Impellers
• Destroys Wear Plates
• Ruins Mechanical Seals
(Vibration & thrust loads)
Total Dynamic Suction Lift Too “HIGH”
Discharge Head Too “LOW”
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Chemical Attack
Abrasive Wear
Discharge Cavitation
Suction Cavitation
Shaft Breakage Problems
Radial Fatigue Break
• Total Dynamic Head Too “High”
• Air (Hydraulic Imbalance)
• Mechanical Imbalance
Torsional Break (Twisting Break)
• Pump Lock-UP
• Reverse Rotation (Open Check Valve)
• Short Cycling
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