How to increase centrifugal impeller speed
How to increase centrifugal impeller speed
(OP)
1. How do the pump manufacturers determine the pump speed or RPM?
2. A motor with a constant speed rotates the impeller at the same speed. Hence higher the motor speed, the larger the impeller RPM.
3. Higher the motor hp, larger the motor speed. So one way to increase the pump RPM is to upgrade the motor hp and speed.
4. A motor can be sped up by more than 100% with a carefully chosen VFD.
Are the above statements correct? if not, why? Thanks for your comments/answers in advance.
2. A motor with a constant speed rotates the impeller at the same speed. Hence higher the motor speed, the larger the impeller RPM.
3. Higher the motor hp, larger the motor speed. So one way to increase the pump RPM is to upgrade the motor hp and speed.
4. A motor can be sped up by more than 100% with a carefully chosen VFD.
Are the above statements correct? if not, why? Thanks for your comments/answers in advance.





RE: How to increase centrifugal impeller speed
3. false.
4. Mostly false. VFDs can overspeed AC motors, but the current, and hence the power, must be derated. It's just not good practice to size a pump so that it needs an overspeeded motor to get the performance you want, and it's not as easy as you think it is.
Mike Halloran
Pembroke Pines, FL, USA
RE: How to increase centrifugal impeller speed
RE: How to increase centrifugal impeller speed
Mike Halloran
Pembroke Pines, FL, USA
RE: How to increase centrifugal impeller speed
RE: How to increase centrifugal impeller speed
Mike, your statement #4 is not correct. A VFD can overspeed a motor, within mechanical stress limits, and its power output will increase. The maximum torque of the motor is limited by its current rating for thermal reasons. So double the speed at constant torque will give double the horsepower. But again, the load determines the power required from the motor, and doubling the speed of a pump requires something like 8 times the power, depending on a number of other factors.