Is there a cavitation-free pump operation?

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A question was asked if a pump operation could be cavitation-free.

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All pumped liquids have vapor pressure to a varying degree. They also have entrained or dissolved gas no matter how small is the amount. Thus, all pumps will experience some form of cavitation, and a cavitation-free operation is non-existent, for as long as any of these elements are present in the liquids.

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Cavitation, per se, can be harmless and not objectionable. Stable cavitation condition, or onset of cavitation, can be acceptable. What is more important is to identify when does cavitation become detrimental enough for it to cause degradation of pump performance, or damage to the pump, such as in the event of transient cavitation. The pump industry set a 3% head loss as threshold for acceptable cavitation, hence the concept of NPSHR3. But in many high speed or high energy pumps, or in pumps handling liquids with high gas content such as carbonates, NPSHR3 has proved to be critically inadequate. Many engineers looked into the alternative concept of NPSHR1 (1% head loss), or NPSHR0 (0% head loss), as the threshold to guard against cavitation damage. Based on extensive historical testing, NPSHR1 or NPSHR0 can be estimated empirically with accurate results.

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A well-known pump expert came up with the concept of cavitation-free NPSHR (NPSHRCF) but that was based on empirical approach and was not supported by tests. Another pump expert came up with a very similar approach but would not buy into the term “cavitation-free” NPSHR. Instead, he referred to his method as the 40,000 HRS NPSHR, i.e., NPSHR for 40,000 hours of operation with no cavitation damage to the pump.

One has to consider also that there are two types of cavitation in pumps: the first is classical cavitation due to inadequate NPSHA, and the second one is cavitation induced by low flow internal recirculation. NPSHR3, and the other alternative NPSHR concepts, ?address the issue of classical cavitation only.

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Cavitation induced by low flow recirculation, is more difficult to predict because it is not as evident as classical cavitation; it can occur even with sufficient NPSHA. Accurately managing this type of cavitation also requires access to pump hydraulic data that may not be readily available to third parties because they are proprietary information.

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Related article: How to differentiate classical cavitation from cavitation induced by low flow recirculation.

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Tags: #cavitation, #classicalcavitation, #stablecavitation, #transientcavitation, #onsetofcavitation, #NPSHA, #inadequateNPSHA, #NPSHR, #NPSHR3, #NPSHR1, #NPSHR0, #internalflowrecirculation, #lowflowrecirculation

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Disclosure: The author spent his entire professional career with multiple companies in the pump industry. He is now retired and wrote this article in his personal capacity. This article is preliminary for further discussions as each situation is uniquely different. For more information, please email the author at [email protected] .

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