Typical Pump Performance curve

Hi Friends!!!

Today i am going to write on a Pump Performance curve.

Sample Pump Performance Curve.

Referring the above curve , A Pump Performance Curve is basically divided into three parts

Part 1 : Flow Vs Head Curve

Part 2 : Power(BKW) Curve

Part 3 : Efficiency and NPSH Curve.

 

A) Part 1 : Flow Vs Head Curve

a) Flow and Head are always inversely proportional to each other with regards to Centrifugal Pump.

Care has to be taken that pump is selected in such a way that The duty Points(Flow , Head) are selected within 70% to 110% of the Best efficiency points.

b) Impeller Diameter : Based on the Flow and Head , the duty point is plotted on the curve and Impeller diameter is accordingly decided. It is called Rated Impeller Diameter.

In the above curve : Min Impeller diameter  is 225mm and Maximum Impeller diameter is 329mm.

c) Minimum Safe Flow : Below this flow the pump should not be operated. If operated then the life of the pump reduces and also many issues arise.

d) Shut Off Head : This is the maximum head the pump can develop. It is obtained at 0 Flow. So for impeller diameter 329mm , Shut off Head is 150m.

B) Part 2 : Power Curve

a) This curve shows the power taken by the pump to operate at a particular Flow and Head.

b) General formula for Power BKW is

BKW =  [(Flow(m3/hr) X Head(m)) / (367.2 * Efficiency)] * Specific gravity.

C) Part 3 : NPSH and Efficiency Curve.

a) NPSH Curve shows the NSPH Required by the pump. Always it should be noted that NPSH Available should be More than NPSH Required. ie

NPSH A > NPSH R

If the you see on the cure , the more you go on right side the NPSH increases. Hence when the pump is operating at extreme right and we dont have enough NPSH A at site then generally we can throttle the valve and lower the NPSH R of the pump by increasing pressure.

If NPSH is less the available then pump will start sucking air instead of water and it will lead to serious damages to the pump.

b) Efficiency : The pump should be selected at the max efficiency. So that the pump consumes less power.

BEP ( Best Efficiency point) This is the maximum efficiency that particular Pump can give.

D) Miscellenous

a) This curve also covers the Recommended Pipe size. Kindly note that pipe size is most important for correct results. Hence care should be taken to follow the recco given by pump manufacturer.

b) Suction and Delivery Size : This is given inorder to connect it properly with the pipes.

Hope i have made this topic easier. Please feel free to ask any queries or questions and i will be happy to answer them.

Thanks and Regards

Siddharth Bhimani…

Sial Valves Co…Authorised Dealer of Kirloskar Brothers Ltd.