Compositepro is right. Most pumps can only be slowed down by about 10% and still produce the static head, which in your case is 70 PSI. With a 60 Hz motor that would be a minimum of 54 Hz. This greatly limits any benefit from a VFD. You could save yourself a lot of trouble and just use a...
Just get a drive with “sleep mode”, and use a set point of 70 PSI. Then adjust the minimum frequency, according to the pump curve, that will produce the minimum flow required for the pump at 70 PSI. This way you don’t need flow switches or sensors and can spend your time mitigating the other...
I would have the motors checked for cause of failure, turn the soft start down to 2 seconds, and make sure the Submonitor is programmed for manual reset only.
The Submonitor does not work fast enough to catch a bouncing pressure switch. The pump will usually bounce on and off a half dozen times before the Submonitor will kick out on rapid cycle. Then if you don’t have it purposely set to stay off after this trip, it will reset itself and let the...
Booster pump packages can be made with end suction centrifugal pumps, multistage centrifugal pumps, split case, turbine, or just about any kind of pump. You need to pick the most efficient and cost effective pump available for the flow and pressure required, then you can make a ‘booster pump...
I agree with 1gibson. Head is reduced by the square of the RPM. The pump needs to produce enough head to deliver the flow required to keep it from overheating. I think this is what limits the RPM, and is more important in this case than NPSH.
Agreed. But if the windings are not shorted, the wet winding motor will still run where the canned stator is done. I just hope this poster will come back and tell us what they did and how it is working.
How deep the pump is under water has nothing to do with motor cooling. If there is not sufficient flow going past the motor, the water around the motor can boil, no matter how deep the pump/motor is set underwater.
If you overheat a motor with a canned stator, the stator will swell and grip...
As you say, rewindable or "wet winding" motors allow an even greater internal heat rise. So the canned stators of the Hitachi motors in question are a worst-case scenario for heat transfer. I can lay a 30 HP Hitachi motor on a workbench, (not even in water), turn it on and put my hand or a...
You are right, one minute is for 4” motors. The fact that it takes 15 minutes for larger motors further proves that it takes considerable time for the internal heat to transfer to the housing where it can be cooled down. Which should also mean that cooling flow is not required at the instant...
It takes a little time for the heat generated at start up to be transferred to the motor housing. Water flow at the moment of pump start has no heat to work on. Within a minute or so the housing starts to warm and then the water flow can start cooling the motor housing. The motor company...
Thanks for that. I have been saying “closed” valve, but the valve I use is a non-closing type. It is open just a crack when the pump starts. And yes I know larger pumps and pumps with axial or mixed flow impellers are different. The largest pump I have done is 250HP, and the ones I was...
See the chart on page 2 of this link.
http://www.rmhindustries.com/wp-content/uploads/2011/11/brochure-corporative-accouplements-magnetiques-magnadrive.pdf
This shows when the motor is disconnected from the load there is about 15% less peak load at start up and a big difference in time. I...
A person with well experience knows that water under water doesn’t weigh anything to the pump. When there is no check valve and the water in the discharge pipe is the same as the static water level, there is the same head on the inlet of the pump as there is on the outlet. So the pump starts...
Yeah you can drill a hole in a check valve to let the water drain back slowly. That is much better than letting the pump spin backwards. But it is still much harder for a pump to start with empty pipe than with full pipe. It is even easier on the pump/motor to start with the pipe full and...
