First, the diagnosis method of the cavitation erosion of the in-service pump

The user of the pump usually cannot make use of the method adopted by the manufacturer to determine whether the cavitation of the pump occurs or not, that is to say, when the flow rate is at a definite time, the way of cavitation is determined. In addition to the observation method after cavitation damage, ultrasonic method, pump external noise method, vibration method and other methods can be used to judge whether the cavitation erosion occurs in the service pump.

1. Observation method

This method is observed after the event, based on the shape of the damaged surface. The metal surface shape is different from the ideal shape because of the cavitation erosion, the casting hole, the erosion wear and the corrosion. The metal surface of cavitation erosion usually appears honeycomb. It is caused by local high-speed water striking the metal and causing fatigue damage to the metal surface, so the honeycomb hole is usually interconnected with the outside. Most of the pits are perpendicular to the metal surface. The looseness of casting defects is usually hidden inside the metal. Sometimes, due to the erosion of water, the loose porosity and porosity appear on the surface of the metal, which is mistaken for foot cavitation. However, when the surface is removed by mechanical means, it is found that there are still holes in the surface. The scouring wear marks often appear in the same groove as the direction of water flow, but pay attention to whether there is a vortex of water flow.

2. Noise method

This method is simple and can not contact the pump body. But because of the noise in the noise environment by week is larger, when the show its highest intensity. General pump cavitation has reached the stage of a very strong, then the ear has been through a strong burst of cavitation cavitation discriminating condition. Therefore, the pump body noise method is not very suitable for monitoring the occurrence of cavitation erosion in the field. Health level self-priming pump

3. Vibration method

The method of measuring the vibration frequency of the pump body by the accelerometer probe is simple, but the sensitivity is low. Especially for large pumps, the stiffness of the pump body is large. The vibration caused by the slow reaction, local cavitation in pump bubble debacle generated at the same time, the local oscillator pump more. Vibration caused by cavitation is often hidden from other vibrations. Therefore, the vibration method is suitable only as an auxiliary means to monitor the cavitation in the field.

4, ultrasonic method

The ultrasonic method is simple in measuring cavitation, easy to debug and is not disturbed by other ambient noise, and is sensitive to the occurrence and development of cavitation. Therefore, it is an ideal method to monitor the cavitation site at the site of the pumping station.

Two. The method of reducing the cavitation damage of the in-service pump

1. Into the pool

In the field of use, the cavitation (including other failures) of the pump (including other failures) is very necessary and convenient to check the flow of the intake pool. As for whether or not we need to break the vortex plate, we should check the flow of the influent pool at the scene. If we can see the strong vortex on the surface of the pool, we should consider adding the vortex plate. In addition, the geometry of the inlet and the inlet should be paid attention to. For example, whether the distance from the pipe mouth to the wall of the tank is suitable, and whether there are bubbles entering the pump suction pipe.

2. Inlet pipe

The setting of the inlet pipeline should not only minimize the loss of the pipeline as much as possible, but as far as possible, use the elbow and the unnecessary valve as little as possible, so that the inlet pipe must not have a position higher than the inlet of the pump to prevent gas accumulation in the pipe. Can say so, reduce the suction resistance of pipeline, such as increasing the pipe diameter, reducing pipeline accessories, foot valve, elbow, valve etc.. This method can improve the NPSHa value by improving the suction conditions. It is also convenient and practical.

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