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a pump manufacturer
a pump manufacturer
Yes, a pump manufacturer or reseller would or should consider the full load motor speed in calculating impeller trim and so should you as the end user if you are selecting the motor based on the pump curve. On smaller units it is not so important but as pump sizes increase careful consideration becomes necessary and on very large diameter impellers it can be critical as 5 - 6 RPM could plus a motor into overload - remember power increases as the cube of the speed change. Of course all of this depends on the margin between maximum pump demand and the full load power rating of the motor.
Depends on shape of the power curve and the spec requirements.
Motor must be sized for end of curve. Say that is 399hp so you buy a 400hp motor. Your operating point requires 300hp. Shutoff requires 200hp.
Full load speed of your motor is 1180 rpm so the pump curve is set up at 1180. But 3/4 load speed is 1185 and that's the speed the motor is going to run at. 1/2 load speed is 1190 RPM, that can be a pretty large increase in head at shutoff.
Motor must be sized for end of curve. Say that is 399hp so you buy a 400hp motor. Your operating point requires 300hp. Shutoff requires 200hp.
Full load speed of your motor is 1180 rpm so the pump curve is set up at 1180. But 3/4 load speed is 1185 and that's the speed the motor is going to run at. 1/2 load speed is 1190 RPM, that can be a pretty large increase in head at shutoff.
2011-06-03
