The challenge: What are some tips for determining the proper balance between a pump’s flow rate and pressure?

Rain Bird

Bill Beard
General manager

Pumps operate on a flow versus pressure curve. However, the system demand dictates where the pump operates, so matching the pump to the system is critical. DO achieve good balance by setting up irrigation zones that require about the same flow rate. DO calculate the pressure losses in the zones. Taking the time to do these calculations right will make it easy to pick a pump that matches every zone’s need for flow and pressure. DON’T purposely oversize pumps. This results in higher costs and serious performance issues.

Hunter

Robb Kowalewski
Product manager, micro irrigation and valves

DO use the flow control knob, which many valves come equipped with. This often-underutilized feature allows you to regulate the volume of water passing through the valve. An unadjusted valve takes longer to close than a valve with properly adjusted flow control. DO adjust the flow control knob to its lowest setting without limiting necessary system flow. This can also help extend the life of the diaphragm. DON’T forget, flow can and should be adjusted if the operating pressure is too high or if the flow is too low.

SiteOne

Brian Quill
Category manager — irrigation, storm water, aquatics

DO reference the manufacturer’s performance data for your pump model. Referred to in the industry as “pump curves,” the flow and pressure relationship is shown on a curved line that is plotted on a graph. In general, as a pump’s flow rate increases, the discharge pressure decreases. DO determine the performance of any given pump by finding the point on the manufacturer’s graph where the desired flow rate and discharge pressure intersect along the pump curve line. DON’T ignore it if the desired flow rate and discharge pressure do not intersect near the pump curve line on the graph. If they don’t intersect, you’ve got the wrong pump.

Ewing Irrigation

Rick McNabb
Education services trainer/specification specialist – pumps water features

DO determine the pump’s best operating point. This is the point where electrical consumption is best utilized to produce a given flow rate in gallons per minute at a given pressure in psi. DO ensure that the flow is no less than 20 percent below the best operating flow point and no more than 20 percent above the best operating flow point. As long as you stick to that guideline, the pump is considered to be efficient. DON’T have electric voltage to the motor that is 10 percent below or 10 percent above the stated motor nameplate voltage required. Running a pump motor below or above the recommended nameplate voltage will reduce the life of the motor.