Question

For efficiency and flow rate curve for a pump, why does the curve fall off after the best efficiency point? Why does a high flow rate mean higher efficiency?

For hydraulic power vs flow rate curve for a pump, what is the relationship? why does a high flow rate mean higher hydraulic power? concept behind this?

Answer 1

The performance curves of a centrifugal pump are given as follows:

7 Efficiency. Head BEP ( Efficiency Head, n on f rd Hydraulic power ic SE Design discharge - Flow x specific gravity BHP = QX H 3600x Power Q- Flow, Htead, BHP: Brake Horse

The efficiency curve of the centrifugal pump with discharge is as shown below.The flow of a pump varies from conditions of Dead Head condition to Run Out condition.The dead head condition of the centrifugal pump refers to the close discharge valve,where there will be no flowrate.At this condition,the head of the pump is high.Run Out condition of the centrifugal pump refers to the maximum flowrate through the pump,where the pump head is very small.As the discharge through the pump gradually increases,the flow behaviour gradually turns to turbulent flow,so as the efficiency of the pump gradually increases.There after the curve decreases gradually as the flowrate through the pump will be more turbulent,and the pump will be in runout condition where there will be minimal head and the pump gets damaded due to overload and more cavitation results.So due to this reason,te pump is allowed to operate at optimum conditios where the value of efficiency will be more and that point is referred to as Best Efficiency Point.So, more the turbulence,the lesser will be the efficiency.

As we have a direct relation as shown in the equation, between the flow/discharge with power,the hydraulic power increases as the discharge increases.As the pump gets started the hydraulic power also increases from  Dead Head condition to Run Out condition.