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Presse und News des Pumpenherstellers EDUR

Cavitation in pumps

June 29. 2018

Cavitation in pumps: causes, signs and effects

This article presents you frequently asked questions and answers about cavitation in pumps.

 

Cavitation is a fluidic phenomenon that is harmful to pumps. Frequently asked questions on this topic concern the causes of cavitation in pumps as well as the impact on operating performance, reliability and material abrasion.  

 

Basically cavitation is related to the fact, that a substance can assume three different states of matter - solid, liquid and gaseous. Whether a substance is present as gas, liquid or solid is determined by the temperature but also by the pressure.   

 

Causes and signs of cavitation  

The temperature of the pumped medium generally remains quite constant. By entering the pump, the pressure initially drops due to the flow losses and the cross-sectional changes. If the pressure drops to such an extent that the vapour pressure is fallen short of and the pumped medium vaporizes proportionally, gas bubbles form in the flow. This effect, the formation of gas bubbles, is called cavitation.  

The extent of cavitation is influenced by different characteristics of the pumped medium:   

Effects of cavitation for pump systems 

Even the formed cavitation bubbles can influence the delivery behaviour of the pump if they combine to form larger gas accumulations and constrict the flow cross-section. However, it is particularly problematic because the gas bubbles are carried away by the flow and reach areas where the pressure is rising again. The higher pressure forces the gas in the bubbles to return to the liquid state. The bubbles implode abruptly, resulting in fast liquid flows, so called micro-jets.

When these micro-jets come into contact with pump components, strong forces act on the pump surface. Besides loud noises, this results in material damage in the form of so called "cavitation erosion". These damages never appear at the cavitations point of origin, but at a more or less large distance where the vapour bubbles collapse. Existing protective layers on the material are destroyed. This means that the surface can constantly be chemically attacked. In this way, considerable material erosion can occur even by weakly cavitation. Therefore cavitation must be absolutely avoided when operating a pump. For this purpose, it must be ensured by the constructive and installation side that the inflow pressure in the pump inlet - expressed by the available NPSH-value - does not fall below a corresponding minimum.  

 


Cavitation is a fluidic phenomenon that is harmful to pumps



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