The normal sound of water-ring vacuum pump is caused by water-ring eddy current. After the pump exceeds the critical compression ratio, the gas pressure discharged from the pump can not resist the air pressure at the exhaust hole, resulting in the increase of the gas back pressure in the pump, which is transmitted to the water ring and causes the flow rate to slow down. At first, the eddy current is formed in the outer part of the water ring which is close to the pump body between the suction hole and the exhaust hole. Then, with the further increase of the back pressure of the exhaust hole, the range of the eddy current is enlarged, and the volume of the suction space and the effective cross section of the suction hole are gradually reduced, resulting in the decrease of the gas child.
When the critical compression ratio is exceeded, the water ring eddy current forms, which makes the pressure and volume of gas in the pump produce periodic pulsation and causes the sound of the pump. The sound intensifies with the increase of compression ratio (but the shaft power does not increase much). When the maximum compression ratio is reached, the air volume is zero, and the whole water ring from the suction hole to the exhaust hole forms eddy current, which maximizes the air volume fluctuation and noise. This noise is related to the circumferential speed of the pump, the suction pressure, the wall thickness of the pump body, the structure of the gas-water separator and the water supply basin. For running pumps, if the water supply is properly adjusted, the sound may be reduced.
During the operation of water-ring vacuum pump, if the sound is not caused by the above normal hydrodynamic phenomena, but one of the following three cases, it shows that there is a fault in the pump.
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