In general, cavitation in rotary lobe pumps can be divided into four types as follows.
1. Free or moving cavitation
Free cavitation is the creation of bubbles in a flowing liquid, which simultaneously grow in the liquid and collapse at high pressure.
2. Fixed or attached cavitation
Stationary cavitation is the formation of cavities on the surface of an object placed in flow or on the side walls of a flow channel and adheres to the wall surface.
Vortex cavitation is the occurrence of cavities in the low pressure part of the vortex. The cavitation that occurs at the end of a spiral plasma wing is this type of cavitation.
Vibrational cavitation is cavitation that occurs in large amplitude, high frequency pressure pulsating fluids. It is often used to conduct material cavitation damage tests and is not usually seen in hydraulic machinery. Moving cavitation and fixed cavitation often occur in hydraulic machinery.
Measures to avoid cavitation in rotary lobe pumps.
1. In the design, the rate of change of each section of the circulation section should be made small, while the wall through which it passes should strive to be smooth.
2. At a certain suction height, the increase in the number of revolutions of the rotary lobe pump should be limited, because the greater the number of revolutions and the greater the flow, the smaller the suction height. Therefore, increasing the number of revolutions of the rotary lobe pump will inevitably reduce its suction height. Therefore, at a certain suction height, there is a limit to the number of revolutions that can be increased, otherwise cavitation will occur and lead to the destruction of the normal operation of the pump.
3. It is desirable to keep the rotary lobe pump constantly in operation near its design working conditions.
4. Minimising resistance in the inlet pipe, which should therefore be both straight and short, and correctly determining the suction height of the rotary lobe pump.
5. Use appropriate materials for components in areas prone to cavitation.