Answers to
frequently asked questions
A pump performance curve is a graph that shows the relationship between the flow rate and the head of a pump. It is also known as a pump efficiency curve, pump selection curve, pump characteristic curve, or simply a pump curve. The curve is generated by the pump’s original equipment manufacturer and provides information on how different parameters like NPSH required, efficiency, and power requirement will behave when the flow is changed.
Reading a performance curve is essential on application variables such as:
Head (water pressure)
Flow (the volume of liquid you have to move in a given time period)
A pump curve shows the two performance factors on the X,Y axis so you can see the volume of fluids a pump can transfer under various pressure conditions. Other variables include:
RPM
Impeller size, as they related to pump performance
Power
Efficiency
Net Positive Suction Head (NPSH) in centrifugal and positive displacement pumps
WHAT IS HEAD?
Head is the height to which a pump can raise water straight up. Common units are feet of head and pounds per square inch. (A pump curve calculator might offer different units such as Bar or meters of head).
Flow is the volume of water a pump can move at a given pressure.
FORMULA is FEET OF HEAD/2.31 = PSI
In addition to head and flow, most pump performance curves will also provide efficiency information. Special attention should be paid to the location of best efficiency point (BEP) relative to the operating condition. Pumps run best at or near BEP. For this reason, the Hydraulic Institute has defined a pumps Preferred Operating Region (POR) as flows from 70% to 120% of flow at BEP for most centrifugal pumps.
The pump curve will tell you whether it is able to efficiently perform the required flow rate at a certain pressure, and therefore whether it is suitable for your application. This is the most widely used function, although it can also be used to determine the required power to operate. Selecting a pump that operates too far to one side of the curve can cause pump damage, poor performance and unnecessary energy consumption.
