AC Pump flow fluctuations

[Bradford75]

Looking for help understanding why a power cycle of an AC pump would cause a different flow rate upon powering on.

I'm not concerned with the specific flow rate but rather the fluctuations as the changes are causing adjustment of the gate valve on my herbie overflow and sump level alarms either higher or lower causing the ATO to reduce the salinity.

Here's the scenario a pump will flow 370 gallons and consuming 48 watts. After powering off for > 10 min it will flow 394 GPH and consume 44 watts. Then if power cycled quick off and on it will go back to the lower flow rate and higher wattage.

I've cleaned and inspected the pump it seems fine. What is going on here?

What is also confusing is the wattage relationship. At 370 GPH I would assume less RPM and thus less wattage draw but it's 4 watts higher than when flowing 394 GPH. I've also throttled it back using a gate valve from 394 to about 370 and the wattage drops as expected to around 42 watts. So something different is happening here. Is it possible the impeller is spinning backwards?

 

[Pistondog]

Looking for help understanding why a power cycle of an AC pump would cause a different flow rate upon powering on.

I'm not concerned with the specific flow rate but rather the fluctuations as the changes are causing adjustment of the gate valve on my herbie overflow and sump level alarms either higher or lower causing the ATO to reduce the salinity.

Here's the scenario a pump will flow 370 gallons and consuming 48 watts. After powering off for > 10 min it will flow 394 GPH and consume 44 watts. Then if power cycled quick off and on it will go back to the lower flow rate and higher wattage.

I've cleaned and inspected the pump it seems fine. What is going on here?

What is also confusing is the wattage relationship. At 370 GPH I would assume less RPM and thus less wattage draw but it's 4 watts higher than when flowing 394 GPH. I've also throttled it back using a gate valve from 394 to about 370 and the wattage drops as expected to around 42 watts. So something different is happening here. Is it possible the impeller is spinning backwards?

What is the change in aquarium water height from start after > 10 minutes off to steady state?
In my tank, its about 1/2 inch higher than with the pump off.
This would slightly increase head pressure and might cause the symptoms you are describing.

 

[Bradford75]

What is the change in aquarium water height from start after > 10 minutes off to steady state?
In my tank, its about 1/2 inch higher than with the pump off.
This would slightly increase head pressure and might cause the symptoms you are describing.

Thanks I didn't think about that but I checked and the difference in water drop with the pump off is the same. The over flow will drain to same level and drop the DT by about 1/2" as well. (return has a check valve and syphon break)

I've also used the gate valve on the return to dial back the pump from 394 to around 370 and upon opening the valve it will come right back up to 394 so the pump should be able to over come a change in head pressure when it's removed again.