Pump Cavitation Definition
Pump cavitation is the formation and subsequent collapse or implosion of vapor bubbles in a pump. It occurs when the absolute pressure on the liquid falls below the liquid’s vapor pressure. When the vapor bubbles collapse with high enough frequency, it sounds like marbles and rocks are moving through the pump. If the vapor bubbles collapse with high enough energy, they can remove metal from the internal casing wall, and leave indent marks appearing like blows from a large ball pein hammer.
Inadequate NPSH available (NPSHa) is a root cause for cavitation in the pump. Insufficient NPSH leads to lower liquid pressure in the pump and if pressure in the eye of the impeller falls below the vapor pressure of the fluid, then cavitation can begin by formation of vapor bubbles.
Symptoms and Effects of Pump Caviation
Pump cavitation causes noise and vibration. If the pump operates under cavitating conditions for a long time, the following damage can occur:
- Pitting marks on the impeller blades and on the internal volute casing wall of the pump
- Premature bearing failure
- Premature mechanical seal failure
- Shaft breakage and other fatigue failures in the pump
Other problems caused due of pump cavitation
- Problems with pump packing.
- Problems with mechanical seals.
- Problems with alignment.
- Problems with the bearings.
- Problems with impellers, casings, and wear bands.
- Problems with pump efficiency.
And these problems won’t go away until you resolve cavitation at its source.
Types of pump cavitation
- Vaporization cavitation, also called inadequate NPSHa cavitation.
- Internal re-circulation cavitation.
- Vane passing syndrome cavitation.
- Air aspiration cavitation.
- Turbulence cavitation.