motor slowing down?

[joshgarcia]

Here at my plant we have two pumps side by side and one is building more pressure and GPM flow than the other. They replaced the pump and didnt gain much. I have meggered the motor (50 Gohms) and tried my best to explain that the motor is not the issue, that motors dont just slow down over time. It is a standard 480V 3 phase motor 3550 RPM motor. My question is, am I right or is there something I have yet to learn? Thanks

 

[Harry Mathews]

Is the motor on a VFD?

 

[K8MHZ]

Are you sure the problem is the motor slowing down? Have you used a tach to measure the speed of the motors?

Your problem may not be electrically related. Is the head pressure to both pumps the same?

Also, I don't see where a motor slowing down would increase both GPM and pressure, they would decrease.

I could see eroded impellers decreasing both, but not increasing both, as well.

 

[zog]

Here at my plant we have two pumps side by side and one is building more pressure and GPM flow than the other. They replaced the pump and didnt gain much. I have meggered the motor (50 Gohms) and tried my best to explain that the motor is not the issue, that motors dont just slow down over time. It is a standard 480V 3 phase motor 3550 RPM motor. My question is, am I right or is there something I have yet to learn? Thanks

As long as frequency is the same, speed will be the same Speed=120*Hz/#poles

 

[hockeyoligist2]

Is the pump cavitating, louder than the other one? Is it belt drive or direct? Fed from a wetwell? There could be restrictions in the lines feeding the pumps. If fed from a wetwell the intake of one pump could be closer to the incoming liquid and causing cavitation from air in the liquid.

Do they have the same amount of piping, valves, and number of bends? Are you sure all valves are open? These can reduce and increase head pressure.

 

[Besoeker]

Here at my plant we have two pumps side by side and one is building more pressure and GPM flow than the other. They replaced the pump and didnt gain much. I have meggered the motor (50 Gohms) and tried my best to explain that the motor is not the issue, that motors dont just slow down over time. It is a standard 480V 3 phase motor 3550 RPM motor. My question is, am I right or is there something I have yet to learn? Thanks

The pump sets are the same rating?

If the motors are operating directly from the supply (no VSD) then the speed won't vary by very much in normal operation - by less than 1.4% from no load to full load for 3550 RPM you gave. Below 3550 RPM, the motor current would be above its rating and you might expect thermal or overcurent protection to operate.

I'm with the others here. If the two pumps and motors are specified to be the same, then it seems more likely to be a hydraulic issue. Maybe the problem is the pump that is producing a lower pressure and flow?