by Robert X. Perez

1)  Only select pumps with suction specific speeds less than 11,000-less than 9,000 is even better.

2)  Select your pump so it never operates below 70 percent to 80 percent of its best efficiency point.

3)  Remember that 1800-rpm pumps are usually more reliable than 3600-rpm pumps

4)  Hydraulic efficiency peaks at specific speeds between 2000 and 3000 and drops dramatically below a specific speed of 500. Higher efficiency means less vibration and noise and lower energy bills.

5) Use double suction impeller sparingly. They are less stable at off-design conditions than single suction impellers.

6)  For single stage pumps never select a pump with a maximum diameter impeller. You may need to increase the impeller diameter in the future.

7)  Select a driver that allows you to operate to the end of the pump curve.

8)  Use hydraulic stability, not temperature rise, as criteria for setting the minimum acceptable pump flow.

9)  Incorporate a healthy NPSH margin or ratio, i.e. NPSHr/NPSHa into your selection. This ratio should be anywhere from 1.1 to 2.0 depending on the fluid, criticality and suction energy level. A higher value is always better.

10)  Consider fluid volatility when making your pump selection. Be more conservative when the fluid has a single boiling point, as opposed to a fluid with a wide boiling point range.


Editor's Note: To read about how Pumps & Systems' PumpCalc helps Pump Designers, click here.