Noisy pump running at max RPMs with low GPM

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D

dpetty

0
Jul 5, 2011
5
Pool Size
30000
Surface
Plaster
Chlorine
Liquid Chlorine
I have a 12 yr old Pentair VF pool pump (and 12 yr old 30k gal in-ground pool) that has been running pretty well. Note: I serviced the wet side gaskets a few years ago.
I have a Pentair FNS 60 filter that I break-down every few months....so its clean. Grids were replaced 2 years ago.
The pump has gotten increasingly noisy on the motor side (107db) but quieter on the wet side (80 db).
Its more of a loud humming sounds vs a grindy sound.

I noticed that the pump hits max RPMs (3450) at just 40 GPM...which seems really low for max RPM.
The Pentair VF allows you to continue to increase the GPM, however when I do this, the RPMs don't change so I assume the GPM is truly maxing out at 40.
One other thing, when I bypass the filter (recirc mode) at 40 GPM, the RPMs drop by about 1000 RPM to 2430. I am guessing this is to be expected...but that's a huge drop.

Any thoughts on why my pump is spinning at such high RPM (3450) at such a low GPM (40)?
And is it normal for the filter to push up the RPMs by 1000 to achieve the same flow rate vs bypassing the filter?
Could this be due to the age of the motor? (12 years)
 
Last edited:
dpetty said:
I noticed that the pump hits max RPMs (3450) at just 40 GPM...which seems really low for max RPM.
The Pentair VF allows you to continue to increase the GPM, however when I do this, the RPMs don't change so I assume the GPM is truly maxing out at 40.
Click to expand...
That indicates a very large amount of head loss in the system

dpetty said:
One other thing, when I bypass the filter (recirc mode) at 40 GPM, the RPMs drop by about 1000 RPM to 2430. I am guessing this is to be expected...but that's a huge drop.
Click to expand...
No, not expected. Too much of a change. This indicates that issue is with the filter. What is the filter pressure?
 
mas985 said:
That indicates a very large amount of head loss in the system


No, not expected. Too much of a change. This indicates that issue is with the filter. What is the filter pressure?
Click to expand...
Currently 25 psi. After fresh rebuild, my pressure is typically 20
 
I have a Pentair 172288 spring check valve in front of my chlorine tablet dispenser. Do those check valves often go bad/get stuck there by reducing flow?
 
Yes, they can get stuck but since you have a large drop in filter pressure in bypass mode, that would still indicate a filter issue.

Let's try this. Put the Intelliflo into RPM mode (not GPM mode) and set RPM to 3450. The Intelliflo has a "Pump Pressure" output in it's display. Post the pump pressure in filter mode and in bypass mode at full speed.

Also, the picture is showing all the suction ports as being closed. I am assuming that was for some maintenance but they should all be open at least for the above test.
 
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