Sixty Seconds With Summit Pump : Vol 1-21 NPSHR and Impeller Diameter.




NPSHR and impeller diameter

Okay, this may take longer than 60 seconds.
Prior to computerized software for pump selection, manufacturers simply drew one NPSHR curve for the pump on the head versus capacity curve. It was used regardless of the impeller diameter chosen. This is not a good idea for the smaller diameter selections.
NPSHR for a fixed flow rate is less for the larger diameter impeller than the smaller diameter impeller. Or stated in another way, at a given flow rate the NPSHR increases as the diameter of the impeller decreases. (Note the head changes but the flow rate remains at some fixed value.)


Comparision between a full and a trimmer impeller
Credit: Comparision between a full and a trimmer impeller by Summit Pumps


As an alternative method to thinking about the science behind this, open your Summit Select program and select a Summit Pump model as below:



You will note that for 250 GPM the 6.00 inch impeller will require about 11 feet NPSHR, the 4.63 inch impeller will require 13.3 feet NPSHR and the minimum 4.00 inch impeller will be 18 feet NPSHR.


Chart showing NPSHR against US gpm
Chart showing NPSHR against US gpm
Chart showing NPSHR against US gpm
Credit: Chart showing NPSHR against US gpm by Summit Pumps

The 3 condition points for the 2 x 3 – 6 (3500 RPM).



"Need a trim and balance? We can trim and balance your impeller for your pump or loose shipment."


Photo of a impeller
Credit: Photo of a impeller by Summit Pumps


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