What is cavitation?

Cavitation is the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller. The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing.

Cavitation

Cavitation is one of the most searched topics on fluid power, which is justified, because cavitation is unfortunately an all-to-common cause of pump damage. Liquids are able to hold dissolved gasses in solution, and the gas saturation level within any liquid is dependent upon the pressure, the temperature and the type of liquid itself, amongst other things. Cavitation is literally the bubbles spontaneously formed during conditions that prevent the liquid from holding that gas in saturation, such as a drop in relative pressure.

Cavitation

Consequences of Cavitation

If left untreated, pump cavitation can cause:

  • Failure of pump housing
  • Destruction of impeller
  • Excessive vibrations- leading to premature seal and bearing failure
  • Higher than necessary power consumption
  • Decreased flow and/or pressure

There are two types of pump cavitation: suction and discharge.

Suction Cavitation

When a pump is under low pressure or high vacuum conditions, suction cavitation occurs. The pump is being “starved” or is not receiving enough flow. When this happens, bubbles or cavities will form at the eye of the impeller. As the bubbles carry over to the discharge side of the pump, the fluid conditions change, compressing the bubble into liquid and causing it to implode against the face of the impeller.

An impeller that has fallen victim to suction cavitation will have large chunks or very small bits of material missing, causing it to look like a sponge.

Cavitation

Possible causes of suction cavitation:

  • Clogged filters or strainers
  • Blockage in the pipe
  • Pump is running too far right on the pump curve
  • Poor piping design
  • Poor suction conditions (NPSH requirements)

Discharge Cavitation

When a pump’s discharge pressure is extremely high, or runs at less than 10% of its best efficiency point (BEP), discharge cavitation occurs. The high discharge pressure makes it difficult for the fluid to flow out of the pump, so it circulates inside the pump. Liquid flows between the impeller and the housing at very high velocity, causing a vacuum at the housing wall and the formation of bubbles.

As with suction cavitation, the implosion of those bubbles trigger intense shockwaves, causing premature wear of the impeller tips and pump housing. In extreme, discharge cavitation can cause the impeller shaft to break.

 

Cavitation

 

Possible causes of discharge cavitation:

  • Blockage in the pipe on discharge side
  • Clogged filters or strainers
  • Running too far left on the pump curve
  • Poor piping design

Cavitation Prevention

If your pumps are experiencing cavitation, check these things to troubleshoot the problem on your own:

  1. Check filters and strainers – clogs on the suction, or discharge side can cause an imbalance of pressure inside the pump
  2. Reference the pump’s curve – Use a pressure gauge and/or a flowmeter to understand where your pump is operating on the curve. Make sure it is running at its best efficiency point
  3. Re-evaluate pipe design – Ensure the path the liquid takes to get to and from your pump is ideal for the pump’s operating conditions

 

References

https://blog.craneengineering.net/what-is-pump-cavitation

7 ways to avoid cavitation

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