Cavitation:

The flow area at the eye of the pump impeller is commonly smaller than either the flow area of the pump suction piping or the flow area by the impeller vanes. While the liquid being pumped enters the eye of a centrifugal pump, the decrease in flow area results in an increase in flow velocity accompanied through a decrease in pressure. The greater the pump flow rate then the greater the pressure drop among the pump suction and the eye of the impeller. If the pressure drop is large enough, or if the temperature is high sufficient, the pressure drop might be enough to cause the liquid to flash to vapor while the local pressure falls below the saturation pressure for the fluid being pumped. Some vapor bubbles formed through the pressure drop at the eye of the impeller are swept along the impeller vanes through the flow of the fluid. While the bubbles enter a region whereas local pressure is greater than saturation pressure farther out the impeller vane, the vapor bubbles abruptly collapse. That procedure of the formation and following collapse of vapor bubbles in a pump is known as cavitation.

Cavitation in a centrifugal pump has an important effect on pump performance. Cavitation degrades the performance of a pump, conclusion within a fluctuating flow rate and discharge pressure.

Cavitation could also be destructive to pumps internal components. While a pump cavitates, vapor bubbles form in the low pressure region straightly behind the rotating impeller vanes. Those vapor bubbles after that move toward the oncoming impeller vane, whereas they collapse and cause a physical shock to the leading edge of the impeller vane. That physical shock creates small pits on the leading edge of the impeller vane. Every individual pit is microscopic in size other than the cumulative effect of millions of these pits build over a period of hours or days could literally destroy a pump impeller. Cavitation could also cause excessive pump vibration that could damage wearing rings, pump bearings, and seals.

A small number of centrifugal pumps are designed to operate below conditions whereas cavitation is unavoidable. Those pumps have to be specially designed and managed to withstand the small amount of cavitation which occurs in during their operation. Mainly centrifugal pumps are not designed to withstand sustained cavitation.

Noise is one of denotes in which a centrifugal pump is cavitating. A cavitating pump could sound such a cold of marbles being shaken. Other denotes which could be observed from a remote operating station are fluctuating discharge pressure, flow rate and pump motor current. Methods to stop or avoids cavitation are presented in the subsequent paragraphs.