What is the relationship between pump head and GPM on a pump curve?

The relationship between pump head and GPM (gallons per minute) on a pump curve is characterized by the principle that head is proportional to the square of the flow rate. This means that as the flow rate increases, the head that the pump can generate increases at a rate that is a function of the square of that flow rate.

In practical terms, this reflects how changes in the flow rate impact the energy required to move water through the system. When flow increases, the resistance and friction in the piping system also increase, requiring more energy to maintain that flow. Thus, the pump must work harder at higher flow rates, resulting in greater head in terms of overcoming that resistance.

This relationship is fundamental to understanding how pumps perform at different operating points and is critical when selecting pumps to ensure they operate efficiently for the expected flow rates in a system. It highlights the need for careful consideration of the system's demands and the pump's characteristics when designing plumbing systems or selecting equipment.