Calculating Suction and Discharge
According to Gorman-Rupp's Jim Widrick, to match the right pump type and size to the job, you should consider the suction and the discharge independently. Here's his advice about these two considerations:
Suction: Determine the friction loss head, or the head required to overcome the resistance to flow in the pipe and fittings. Typically, this depends upon the size and type of pipe flow rate, and the nature of the liquid. Then add the static suction lift (SSL) and the friction loss (FL) together.
Discharge: Conduct similar calculations. Take a look at the static elevation difference, and add this number to the friction loss for a total dynamic discharge head - or the actual height to which water is to be pumped from the water level at the source to the delivery tank - taking into account the friction loss created by the movement of water through the delivery pipeline.
Next, add the suction and discharge calculations together to achieve Total Dynamic Head.
"Now, take a look at a pump performance curve (see below) to determine the maximum point of operation -- the point on the curve where your pumps' performance is to be achieved," says Widrick. "Keep in mind, the No. 1 thing professionals of all types frequently forget is to consider whether the pump being considered can actually deliver the minimum flow rate required for a given suction lift."
He adds, "Without these careful calculations, it's easy to put a good pump into a wrong situation. If all else fails, call a pump specialist. He or she should be able to help you calculate the right factors, as well as other relevant aspects, including pump efficiency differentials and anticipated total cost of ownership."