Question

what are centrifugal pumps and what is cavitation?

Answer 1

Centrifugal Force is force acting on a rotating body causing it to move away from the center of rotation.A Pump is used to transport liquid from one location to another separated by either height or distance or both.

A Centrifugal Pump acts on the principal of centrifugal force.There is an impeller installed in the case, and this liquid enters the impeller eye (hole at the center area of the impeller) and then moves radially out using vanes/blades of the impeller.The rotating impeller has curved vanes increasing in area in the outward direction.The liquid after gaining velocity moves through the volute of the case and then goes out from the discharge flange of the case.

The impeller imparts motion to the liquid in radial direction and increase the velocity of the liquid. The purpose of case is to convert that velocity into pressure. The pressure of liquid coming out of the pump will always be greater than the pressure when liquid was going into the pump.

The impeller is attached to a shaft, which is then attached to a motor. There is a coupling installed between pump and motor. The purpose of coupling to connect the two together. The bearings are installed in bearing housing to support the shaft (radial and thrust loads).

Cavitation

Cavitation is formation of cavities or bubbles in the liquid ,usually near the impeller,which on collapsing creates an intense shockwave which causes microscopic pits on impeller surface whose cumulative effect may damage the impeller or vibration damaging the housing, bearings or seal.It is caused due to sudden drop in pressure in the liquid moving through the impeller eye.It causes formation of bubbles and due to pressure fluctuation they collapse.It is formation of vapor at low pressure.It occurs because there is insufficient Net Positive Suction Head available (NPSHa) or not enough pressure at the suction end of the pump.It affects the performance of the pump by creating fluctuating flow rate and discharge pressure.