Why is the flow of the pump too small will occur cavitation phenomenon?

Why is the flow of the pump too small will occur cavitation phenomenon?

Why is it easy to produce cavitation when the inlet flow of pump is lowered?This is because the main performance parameters such as the head, power and efficiency of the centrifugal pump are not fixed, but vary with the flow rate. The curve drawn on a coordinate paper is called the performance curve or characteristic curve of the centrifugal pump. What happens when the flow rate decreases? The disadvantage of throttling adjustment is that the pump flow is small, and the impeller is easy to cause cavitation

Throttling regulation is to change the opening of the valve to change the flow of the pump, that is to say, to change the characteristic curve of the pipeline. The commonly used to regulate the flow of exports, because the entrance throttle makes reduce the inlet pressure caused by cavitation danger.

This is because the impeller of the centrifugal pump rotating speed under the drive of the prime mover, when the valve opening decreases, flow rate is too low, can not be taken away by the friction heat generated by the impeller and the liquid completely, make the temperature of the liquid inside the pump. Thus causing liquid vaporization, forming cavitation. Especially in the power plant, the boiler feed pump is more remarkable. Therefore, when throttling regulation, we should set up recirculation system, increase the output flow of the pump to prevent cavitation. When the feed water rate is reduced to 1/3 of the maximum flow rate, the recirculating gate shall be opened so that the flow of the feed pump will be increased properly to ensure that the liquid temperature in the feed pump does not rise.