HIGH SUCTION ENERGY PUMPS CD) H036
There is no precise definition of a high suction energy pump, but most incorporate some of the following features:
- The peripheral velocity at the outside diameter of the impeller eye.
- Values above approximately 120-ft/sec (36.5 meters/sec) are considered high suction energy.
- The suction speed S of the pump.
- S = nQ2/(NPSH)0.75 where n = rpm, Q = gpm (largest impeller at the bep.) and NPSH = feet.
- Values above about 12,000 are considered high energy. We try to keep most pump applications below 8500.
- The specific gravity of the liquid pumped.
- The higher the level, the higher the suction energy.
- Thermodynamic properties of the liquid.
- Cold water is one of the highest energy liquids, followed by high temperature water and hydrocarbons.
- The geometry of the pump inlet.
- Side suction pumps are considered higher suction energy than end suction.
- The overlap of the impeller vanes.
- Impellers with two or three vanes have higher suction energy than four or more vanes.
- The incidence angle between the inlet impeller vanes and the approaching liquid.
- The greater the angle, the greater the turbulence and suction energy level. This value may have to be obtained from the pump manufacturer.
- The geometry of the inlet piping to the pump.
- Piping turns and pipe size changes add to the suction energy of the pump.
- Operation away from the best efficiency point (BEP) of the pump.
- At reduced rate of flow, the pump may operate in its suction recirculation region, which considerably increases suction energy.
As of this writing, no one has yet come up with a single equation to tie all of these factors together.
And one last thing, high energy pumps are prone to cavitation