Cavitation phenomenon and suction height of centrifugal pump

1) Because the suction pump relies on atmospheric pressure to put the water pressure into the pump, the pressure at the entrance of the pump is lower than the atmospheric pressure. However, the inlet pressure of the pump can not be lower than the saturated steam pressure at the time of the water temperature, otherwise the water will produce vaporization, and the gas dissolved in the water will also escape, forming small bubbles of steam mixed with the escaped gas. After these bubbles enter the centrifugal pump impeller, with the increase of pressure, the vaporized water vapor condenses into water, the volume shrinks sharply, forming a local vacuum, the surrounding water has a great impact on the vacuum, and constantly acts on the impeller, making the centrifugal pump impeller produce fatigue, and the surface metal fall off; At the same time, the active gas escaping from the water with the heat released by water condensation produces chemical corrosion on the metal, so that the pump impeller soon appears honeycomb pitting, and gradually forms a void, which is called cavitation phenomenon.

2) When the pump cavitation, will produce vibration and noise, flow, head, power and efficiency will be significantly reduced, serious will appear cut-off. Therefore, the centrifugal pump can not work in the case of cavitation. If the pump head drops by 1%, cavitation is generally considered to have occurred.

3) The main factors affecting the centrifugal pump cavitation are the suction height of the pump, the resistance of the suction pipe, the flow speed, and the atmospheric pressure and working water temperature at the installation site of the pump. The atmospheric pressure at the installation site of the centrifugal pump is generally unchanged, and the change in resistance, flow rate and temperature is not large, so the main factor affecting the water pump does not cause cavitation is the suction height. The correct determination of the maximum suction height of the pump is of great significance to the installation and normal safe operation of the centrifugal pump.

4) When the pump is working, when the power grid voltage is reduced, the pump speed decreases, and the pump head characteristic curve decreases accordingly. When the zero lift (initial lift) of the pump is lower than the actual lift, the water can not be discharged, and the flow rate is zero. At this time, the energy transferred by the motor to the centrifugal pump will all be converted into heat energy, so that the water temperature in the pump and the pipeline will rise rapidly, and the pump body will be strongly heated and soon damaged. Therefore, the pump is not allowed to work at zero flow for a long time.