Find details of duty. In the above example: Water, 2m suction lift, 15m static discharge (17m total static head), 360 meters of 150mm schedule 40 steel pipe.
Draw a chart with flow on bottom scale and head on left scale. Estimate scale required based on size of existing pump, or guess maximum flow expected - example shows max flow as 100 L/S and max head as75m - sometimes you just have to guess to get started.
Mark static head. 17m at zero flow. Note: 'Demand' pressure, ie: sprinklers etc, should be added at each flow point, or for approximate figures can be added to static head.
Mark 2 or 3 other points. At 20L/S friction loss is 0.73 m / 100m of pipe, therefore 0.73 x 3.6 + 17 = 19.6 meters. Put mark at junction of 20 L/S and 19.6 m. Repeat for other points. Remember to add static head each time.
Join these points with a line.
You have completed the System Curve. The Curve may have to be extended to suit higher flow pumps.
The pump operating point is where a pump curve crosses the system curve. Draw as many pump curves over the system curve as you like, to see where different pumps will operate, or draw system curve over pump curve.
If pump curve does not cross system curve, the pump is not suitable.
If the pump curve crosses the system curve twice, then the pump will be unstable and is not suitable.
