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LI-NY Tech's Blog

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Centrifugal Pumps and Cavitation

LI-NY Tech

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I recently had a customer whose washing machine would not drain. I attributed this problem to the excess of suds in the tub. The customer seemed skeptical of this diagnosis and so this problem seemed like a good topic to delve further into.

Oversudsing issues are very common in washing machines and dishwashers. Using the incorrect type, or an excess, of detergent can cause an oversuds situation. This often leads to drainage problems. The drain pump cannot pump out overly sudsy water. But why not? It's because of something called cavitation.

Cavitation is the formation of vapor cavities in a liquid. Washing machines and dishwashers use centrifugal pumps. A centrifugal pump needs an uninterrupted supply of water to function properly. The spinning impeller causes the water inside the pump to spin as well, creating centrifugal force, which causes the water to flow away from the center, or inlet, of the pump and out of the discharge port. This displacement creates negative pressure which sucks more water into the pump. Introduction of suds, which are mostly air, into a spinning impeller will interrupt the flow of water and introduce air into the system, disrupting the vacuum being created, and ultimately preventing the pump from being able to discharge the water. This will not be resolved until the suds are eliminated. Fabric softener or vegetable oil can be added to the machine to help to eliminate the suds and allow the pump to finish draining the water.

The video below is a brief introduction to the way in which centrifugal pumps function.

Thanks for reading.

David

RD Appliance Service, Corp.

http://www.rdapplianceservice.com

RD Appliance Blog




8 Comments


DurhamAppliance

Posted

like the cavitation that occurs in my blendtec blender if I try to make a smoothie without enough liquid... the blade winds up turning in an air pocket doing nothing instead of blending.

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Samurai Appliance Repair Man

Posted

A great idea for an education topic for both techs and consumers alike, Brother LI-NY. Thanks for this blog! 

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My favorite line to use.  "These water pumps are good and pumping liquid, but bad at bad at pumping gases.  Which as you know when water suds it is more of a gasous state rather than liquid."  People tend to buy that logic.

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DurhamAppliance

Posted

And Bro MicaBay, you can further explain, in ways I'll leave to your imagination, why being in a gaseous state ain't good. Betcha they'll never forget that lesson.

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Super helpful, bro! I better understand this problem I'm experiencing with the new VMW washers.

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Awesome man, I'm glad you found it helpful.

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