Cavitation is a common phenomenon in hydraulic vane pumps. It will seriously damage the vane pump, which will seriously affect the service life of the hydraulic vane pump, causing social waste and safety accidents that cannot be underestimated. Therefore, it is necessary to study the cavitation phenomenon of the vane pump to prevent the occurrence of the cavitation phenomenon or to minimize the influence caused by the cavitation phenomenon.

How does cavitation occur?

Simply put, the pressure somewhere in the pump drops below the saturated vapor pressure below this temperature, and air bubbles are created in the liquid. In addition, the gas dissolved in the water will also precipitate. The separated vapors and bubbles are transported to the high-pressure region by the flowing liquid, where they burst quickly (at this time, the duration T≤0.001s), and the pressure is excessively increased, which leads to this situation. This process has all the characteristics of rupture, and the impact phenomenon generated in this way will quickly spread in turn, and then the bubbles near the corroded surface and the bubbles in the pores (micropores, cracks, cracks, etc.) will burst. . In this way, cracks may occur where the strength is relatively low. In contrast, the bombardment of the surface caused by the bursting of the bubbles causes the material layer near the cavitation region to vibrate and be damaged.

There are several possible causes of cavitation:

1) The highest point of inhalation is too high or the highest point of perfusion is low.

2) Exceeding the rated flow, so the water flow in the pump increases and the pressure drops.

3) From the perspective of kinematics, the direction of the streamline will never be correct, the flow direction will change rapidly, and the liquid flow at the inlet of the impeller will never be uniform.

The formation of cavitation depends on the operation of the suction area of ​​the pump. Changes in suction conditions will directly affect the occurrence of cavitation and continue to occur.

2. Location of cavitation damage

Both the impeller blades and the wall of the pump's overflow section can be damaged by corrosion, corrosion and cavitation. Based on the observations of various vane pumps over the years, the location of the damage and the position of the flow channel in the pump can be concluded that the location of the cavitation damage is the location where the bubble burst position moves further inward. Flow direction.

In the initial stage of cavitation, the bursting of bubbles is within the range of the impeller. During the cavitation expansion phase, most of the bubbles have been destroyed within the impeller range, and the remaining bubbles will continue to flow to the lower part of the guide vane, volute and multi-stage pump. The bubbles burst there and generated steam there. Erosion occurred.

1) Damage caused by cavitation of the centrifugal pump the damage point is not limited to the blades, so above the impeller cover, the lowest pressure area is located at the front of the impeller blades near the inlet b, where the sudden pressure is there Rise, which may cause cavitation. When severe cavitation occurs, cavitation damage also occurs at the blade outlet, the tongue of the pump, and the induction wheel of the pre-spinned liquid.

2) The oblique flow pump and axial flow pump are located at the damage point of the impeller cavitation : near the impeller inlet c.

The tail of the impeller blade and the pump body corresponding to the end are located at d.

The suction above the bell tube is close to the impeller inlet e.

At the entrance f of the guide vane.

3. Cavitation signs

If the pump lift and efficiency are greatly reduced, noise and vibration may occur, and cavitation can be basically determined. Once the pump flow exceeds the rated value, the possibility of cavitation increases.

4. Prevent cavitation

Measures to prevent cavitation and reduce cavitation damage can be divided into three categories:

(1) Structural considerations

1) In the case of the same flow rate, please use a double suction pump instead of a single-stage pump. This will reduce the flow through the impeller and the required cavitation margin.

2) Use pre-spin. If the pre-rotation along the impeller rotation direction is not very strong, cavitation can be reduced and the pumping performance of the pump can be improved. In addition, the efficiency of the pump can be improved.

3) An impeller with a large exit width can achieve good results.

4) Avoid sharp turns behind the impeller.

5) When the number of blades is even, the entrance of the second blade is shortened each time.

6) Use a gently curved front cover.

7) Increase the number of blades with high specific speed.

8) Thinn the inlet end of the blade.

9) Use a smaller blade entry angle.
10) Use a spiral induction wheel behind the centrifugal pump impeller inlet.

11) An ejector is installed behind the impeller inlet to increase the pressure at the impeller inlet and increase the suction height of the pump (reducing the required filling height).

(2) Preventive measures for installation and operation technology

1) The smaller the maximum suction point of the pump, the better.

2) Reduce the temperature of the conveying medium as much as possible.

3) When transporting hot water, ensure sufficient pouring height.

4) The pump should be operated in the most efficient place.

(3) Cautions on materials Although there is no material that is completely resistant to cavitation, the cavitation resistance of various materials is still very different.

1) For cavitation-causing metals, forged metal is much better than cast metal.

2) A smooth surface is better than a rough surface.

3) High surface hardness is better than low surface hardness.

4) Spraying the surface (painting plastic, spraying silicon carbide, etc.).

Hydraulic Vane Pumps   consists of vane pump and hydraulic pump. It works by converting power into mechanical power for hydraulic energy, making everyday operations easy. Zhejiang Yongling Hydraulic Machinery Co., Ltd. is a professional manufacturer and supplier of hydraulic vane pumps in China. Our products have won a good reputation in China for their stable and reliable quality, and applied to the torch tower of the 2010 Asian Games. Our products occupy most of the domestic market and are exported to Southeast Asia, Russia, Africa and other foreign markets. https://www.china-vanepump.com