What Is Pump Cavitation

May 06, 2026

 

1, Cavitation phenomenon

When the pressure of a liquid is reduced to the vaporization pressure at a certain temperature, bubbles are generated in the liquid. This phenomenon of generating bubbles is called cavitation. The bubbles generated during cavitation, when flowing to high pressure, decrease in volume and eventually burst. The phenomenon of bubbles disappearing into the liquid due to pressure rise is called cavitation collapse.
During the operation of the pump, if the absolute pressure of the pumped liquid in a local area (usually a certain point later in the impeller blade inlet) drops to the liquid vaporization pressure at that temperature due to some reason, the liquid begins to vaporize at that location, producing a large amount of steam and forming bubbles. When the liquid containing a large number of bubbles passes forward through the high-pressure area inside the impeller, the high-pressure liquid around the bubbles causes the bubbles to rapidly shrink and even burst. At the same time as the bubble condenses and ruptures, the liquid particles fill the cavity at a high speed, generating a strong water hammer effect and striking the metal surface at a high impact frequency. The impact stress can reach hundreds to thousands of atmospheres, and the impact frequency can reach tens of thousands of times per second. In severe cases, it can cause wall thickness breakdown.

 

 

The process of generating bubbles in the water pump and causing damage to the flow components due to bubble rupture is called cavitation in the water pump. After cavitation occurs in a water pump, it not only damages the overcurrent components but also produces noise and vibration, leading to a decrease in pump performance. In severe cases, it can interrupt the liquid in the pump and prevent it from working properly.

2, Basic relationship formula for pump cavitation

The conditions for pump cavitation are determined by both the pump itself and the suction device. Therefore, studying the conditions for cavitation should be considered from both the pump itself and the suction device. The basic relationship between pump cavitation is
NPSHc≤NPSHr≤[NPSH]≤NPSHa
NPSHa=NPSHr (NPSHc) - Pump cavitation begins
NPSHa>NPSHr (NPSHc) - Pump without cavitation
In the formula, NPSHa - device cavitation allowance, also known as effective cavitation allowance, the larger the amount, the less likely it is to cavitation;
NPSHr - Pump cavitation allowance, also known as necessary cavitation allowance or pump inlet dynamic pressure drop. The smaller the NPSHr, the better the anti cavitation performance;
NPSHc - critical cavitation allowance, refers to the cavitation allowance corresponding to a certain decrease in pump performance;
[NPSH] - Allowable cavitation allowance, is the cavitation allowance used to determine the operating conditions of the pump, usually taken as [NPSH]=(1.1-1.5) NPSHc.

3, Calculation of cavitation allowance of the device

NPSHa=Ps/ρg+Vs/2g-Pc/ρg=Pc/ρg±hg-hc-Ps/ρg

4, Measures to prevent cavitation

To prevent cavitation, it is necessary to increase NPSHa so that NPSHa>NPSHr. The measures to prevent cavitation are as follows:
1. Reduce the geometric suction height Hg (or increase the geometric backflow height);
2. To reduce the inhalation loss hc, efforts can be made to increase the pipe diameter, minimize the length of the pipeline, bends, and accessories, etc;

 

3. Prevent prolonged operation under high traffic conditions;
4. At the same speed and flow rate, using a double suction pump reduces the inlet flow rate and makes the pump less prone to cavitation;
When cavitation occurs in the pump, the flow rate should be reduced or the speed should be reduced during operation;
The condition of the pump suction pool has a significant impact on pump cavitation;
7. For pumps operating under harsh conditions, anti cavitation materials can be used to avoid cavitation damage.