Pump Cavitation

Ron Bohnak
 / 
March 15, 2017
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“Pump cavitation is, by definition, the formation and subsequent collapse or implosion of vapor bubbles in a pump. This usually occurs when gaseous bubbles are formed in the pump due to a drop in absolute pressure of the liquid below vapor pressure.

The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump and can cause many problems with the pump itself, but can also lead to system problems as well.

There are two types of cavitation: suction and discharge. Both types of cavitation have similar characteristics. Below is a list of possible causes of pump cavitation.

Possible causes of suction cavitation

  1. Clogged wye strainers or filters
  2. Blockage in the piping (check valves, isolation valves, zone valves, to name a few options)
  3. Pump is running too far to the right of the curve (over pumping)
  4. Poor or inadequate piping design
  5. Poor net positive suction head available (NPSHa)

Possible causes of discharge cavitation

  1. Clogged wye strainers of filters
  2. Blockage in piping (check valves, isolation valves, balancing valves, zone valves)
  3. Pump is running too far to the left of the curve (under pumping)
  4. Poor or inadequate piping design

The causes listed above can lead to premature wear of the pumps impeller, pump housing, seals, and bearing assemblies. Cavitation can also cause poor flow conditions which could lead to poor heat transfer and poor system efficiency. (See examples below)

How to prevent cavitation

  1. Check filters, strainers, check valves, balancing and/or flow control valves.
  2. Pump curve – Use a pressure gauge and/or flowmeter to find out where it is operating on its curve.
  3. Re-evaluate piping design – proper piping practices and piping size is important.

Examples of Cavitation:

Examples of Pump Cavitation

Examples of Pump Cavitation

 

 

 

 

 

 

 

 

 

Conclusion: The next time you are called on to inspect or repair a circulating pump that you feel is possibly caveating, be sure to take a little extra time to observe the conditions before making any repairs. Simply repairing the pump is not enough. Find the problem which led to the problem and correct it first. Then you can proceed to make the necessary repairs to the pump. There are many ways to correct the problem if it is related to the incorrect pump. Contact R.L. Deppmann for tech support, replacement parts, pumps, or other solutions, such as VFD’s and balancing valves.

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