If you need Pump, we are China Pump manufcturer.As a Pump Manufacturer, share with you. Often confused with cavitation because of its similar sound, aeration occurs when outside air enters the suction side of the pump. The pressure in the pump suction line is below that of the surrounding atmospheric pressure, so a leak will result in air coming in, not hydraulic fluid coming out. It can be distinguished from cavitation by its somewhat more erratic whining sound. Since the molecules are distributed very evenly throughout the oil, the sound of cavitation is very steady. But the amount of air that leaks into the suction side of a pump is heavily dependent upon the flow of hydraulic oil. The sound will therefore change as changes occur in the machine. Read More