How does the efficiency curve of a well pump shift with speed?

Well pump manufacturers publish "efficiency curves" for well pumps, such as this one (the curve that is most sharply convex down, whose Y axis is read from the "% EFF" scale on the right hand side):

The well pumps are usually sold with a name that reflects the flow rate that yields peak efficiency. So this one is called a "33GS" because it is most efficient at 33 GPM.

These pump curves typically presume a motor speed of 3450 RPM. How might I expect the curve to shift or stretch if the motor speed changes? I'm particularly interested in the range from about 2800 RPM to 3600 RPM.

• 33GS is a range of pumps suitable for different heads with motors varying from 1 to 10 HP. Each pump having a different Curve
Mar 13, 2021 at 5:40
• The % efficiency of the pump head itself is shown as a function of flow rate. There is one % efficiency curve shown for each pump head, regardless of the attached motor. A similar curve—based only on the pump head, independent of the HP of the motor—is shown is other product literature. Mar 13, 2021 at 7:11
• I don't think it's a straightforward question, so I'd recommend you call a Goulds distributor with your question. Mar 14, 2021 at 22:23
• I don't have time to dig into this right now, I don't see a straightforward way to solve this via pump affinity laws, maybe you can go via the specific speed of the pumpe - However I think the best course of action would be to get the data from the manufacturer.
– mart
Apr 12, 2021 at 7:43
• Are the impellers of all the pumps in the 33GS series mutually geometrically similar? And if so, does each pump in the series have a different impeller diameter? Apr 12, 2021 at 10:38