How does the slurry pump prevent cavitation?

  • 08  Aug, 2023

1. The cavitation phenomenon of the pump:

When the liquid is at a certain temperature and the pressure is reduced to the vaporization pressure at that temperature, the liquid will produce bubbles. This phenomenon of generating bubbles is called cavitation. When the bubbles generated during cavitation flow to a high pressure place, their volume decreases so that they burst. This phenomenon of bubbles disappearing in a liquid due to pressure rise is called cavitation collapse.

When the pump is in operation, if the absolute pressure of the pumped liquid is reduced to the vaporization pressure of the liquid at the current temperature in the local area of the flow-through part (usually somewhere behind the inlet of the impeller blade) for some reason, the liquid will be here. When the liquid containing a large number of bubbles passes through the high-pressure zone in the impeller, the high-pressure liquid around the bubbles will cause the bubbles to shrink sharply and burst. While the bubbles condense and burst, the liquid particles fill the voids at a high speed, and at this moment a strong water hammer effect is generated, and the metal surface is hit at a high punching frequency, and the impact stress can reach hundreds to thousands Atmospheric pressure will break down the wall thickness in severe cases.

The process of generating air bubbles and bursting of air bubbles in the water pump to damage the flow-through part is the cavitation process in the water pump. After the pump cavitation occurs, in addition to damaging the flow-passing parts, it will also generate vibration and noise, and cause the original performance of the pump to decline. In severe cases, the liquid in the pump will be interrupted and cannot work normally.

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Second, the basic relationship between pump cavitation

The conditions for pump cavitation are determined by the pump itself and the suction device. Therefore, to study the conditions of cavitation, both the pump itself and the suction device should be considered. The basic relationship of the pump is:NPSHc≤NPSHr≤[NPSH]≤NPSHa

NPSHa=NPSH(NPSHc)－－－－－－－－—The pump starts cavitation

NPSHa＞NPSHr（NPSHc）－－－－－－The pump has no cavitation

In the formula, NPSHa - the NPSH of the device is also called the effective NPSH, the larger the NPSH, the less likely it is to erode;

NPSHr———Pump NPSH, also known as necessary NPSH or pump inlet pressure drop, the smaller the better the anti-cavitation performance;

NPSHc————critical NPSH, which refers to the NPSH corresponding to a certain value of pump performance decline;

[NPSH]－－－－Permissible NPSH is used to determine the operating conditions of the pump, usually [NPSH]=(1.1～1.5)NPSHc.

3. Measures to prevent cavitation:

In order to prevent cavitation, NPSHa must be increased to make 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 suction loss hc, try to increase the diameter of the pipe, and minimize the length of the pipe, elbows and accessories;

3. Prevent working under large flow for a long time;

4. Under the same speed and flow rate, the double suction pump is adopted, and the pump is not prone to cavitation due to the reduced inlet flow rate;

5. When cavitation occurs in the pump, the flow should be reduced as much as possible to reduce the power and speed;

6. The condition of the pump suction pool has an important impact on pump cavitation;

7. For pumps operating under harsh conditions, in order to avoid cavitation damage, cavitation-resistant materials can be used.