A pump curve is a manufacturer's performance chart showing how a particular pump's delivered flow changes with head under stated conditions. It helps compare the pump with the system it will serve. The curve applies to the identified model and configuration, rather than guaranteeing the same flow in every installation.
A pump curve is a manufacturer's performance chart showing how a particular pump's delivered flow changes with head under stated conditions. It helps compare the pump with the system it will serve. The curve applies to the identified model and configuration, rather than guaranteeing the same flow in every installation.
Read both axes and the chart conditions
A common water-pump chart shows flow along the horizontal axis and head along the vertical axis. Check the units before comparing charts. The model, speed, impeller configuration and test conditions identify which curve is relevant.
Zoeller's chart guide explains flow and head, while the Department of Energy's pumping-system sourcebook describes pump and system performance together. Some charts also show efficiency, power or other limits. Only use those additional values where the actual chart provides them and the selection requirements are understood. Where an efficiency curve is supplied, best efficiency point explains the identified peak-efficiency operating point.
The maximum head and maximum flow are different operating points. Reading both as one simultaneous capacity can produce an unsuitable selection. A plotted shutoff head is not a recommendation to operate the pump indefinitely without flow.
The installed system chooses an operating point
The system has its own head requirement at each flow, based on elevation or pressure conditions and losses through the actual route. Its intersection with the applicable pump curve gives the expected operating point for that analyzed condition.
A change in piping, discharge conditions or a restrictive component can change that point. A chart alone cannot establish that the existing line has the assumed dimensions or that every component is in good condition.
The valve flow coefficient entry explains one specification used to interpret a valve's flow behavior.
Selection also has to respect the manufacturer's operating range and the fluid being handled. A chart for a clean-water pump does not approve that pump for sewage, and a general performance curve does not replace solids-handling or electrical requirements. The pump cavitation entry explains a distinct suction-pressure phenomenon that a discharge curve alone cannot diagnose.
What a useful pump proposal shows
Ask for the exact model's chart, the intended flow/head point and the system assumptions used. If an existing pump is being replaced, confirm why the replacement meets the actual duty rather than merely matching horsepower.
Our total dynamic head entry explains the system requirement. The sewage ejector pump entry covers that equipment's purpose. A curve is selection evidence; commissioning verifies the installed operation and any limits that remain.