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Understanding NPSHR and
Centrifugal Pump Cavitation

By Joe Honeywell



It has been said that most pumps cavitate at some point in their life cycle. Some cavitating pumps may go un-noticed for years while others sustain severe damage very quickly. If designers and operators are aware of cavitation issues, why not prevent the problem from occurring? Can manufacturers make pumps that will not cavitate? These are simple questions but the answers are complex.

It is no secret that cavitation should be avoided. There are many organizations, publications, industry standards and company design guides that are quick to explain the pitfalls and harmful effects that occur when pumps cavitate. Most companies have design procedures and equipment selection guidelines that help prevent cavitation problems. Operators and technicians can readily identify the symptoms of cavitation in operating pumps, but are helpless to do anything about it. So, if the problem is common knowledge, frequently discussed and diagnosed, then why does the issue persist? Cavitation is an age old problem that is not as well understood as many believe. It is a complex topic with many aspects that make it difficult to completely comprehend. Every application is different and requires a broad range of knowledge to avoid pump cavitation.

Cavitation is a very technical topic and cannot be explained in just a few pages. Some aspects can be very complex and beyond the understanding of new or inexperienced engineers. For some, a brief review and a general understanding of the effects are all that is required. Sometimes, all that is needed to avoid common mistakes is to apply good design principles to an application. Existing pump systems may require a deeper understanding of cavitation and a detailed analysis to find the root cause. Then again, no action may be needed once the harmful effects of cavitation are better understood. Cavitation is a multi-faceted phenomenon that can range from a simple issue to a far more complicated problem to solve.

This paper will examine what is cavitation and why it occurs in centrifugal pumps. It will also explain what happens inside a pump and the damage that can occur. Preventive measures that users can undertake to prevent cavitation are reviewed. The many effects of pump cavitation are discussed and how they are related to pump systems. In addition, examples are given on how to avoid cavitation in new and existing applications. Finally, this paper will provide recommendations and troubleshooting tips that will help in avoiding cavitation in new and existing pump systems.



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