Pump water level slowly dropping

[thenateo]

Hi folks,

I replaced an old Pentair Whisperflo with a VS Intelliflo yesterday. I started with an 18 hour cycle at 750 rpm as a starting point and checked the pump at about 6 hours in yesterday afternoon. The water started flush with the lid of the basket and at the 6 hour mark it was down maybe a few inches. At about the 10 hour mark it was down to the top of the basket. I shut the pump off at that point because it was getting dark and I was worried about the pump losing prime overnight and running dry for hours. The other threads I've found here suggested maybe there was a suction side leak. However, I ran the pump at full RPM for about 10 seconds and the water level came back to the top of the basket. The pump sat overnight for about 10 hours and this morning the water level was still completely full. Wouldn't a suction side leak cause the water level to drop with the pump completely off? If the pump loses prime in the middle of a cycle, is it smart enough to re-prime itself?

Thanks in advance.

 

[Brett S]

When you have a suction side leak and the pump is off then water will slowly drip out of the leak because there is no suction. When the pump is on and there is suction it will pull air in through the leak. Additionally, as the pump RPM is increased and more water is flowing through the system there is enough flow to pull the air into the pump, through the filter, and out through the returns, that’s why you see the water level rise when the pump is running faster. When the pump is running slower the air can build up in the pump basket because the pump isn’t running fast enough to pull the air through.

From your symptoms it definitely sounds like you have a suction side leak somewhere.

 

[thenateo]

Thanks for the quick reply. If there is a suction side, leak, I see no sign of water anywhere near the pump. I suppose it could be in the plumbing itself.

If that's the case though, with no suction at all, it seems odd to me that after 10+ hours of the pump being off, the water level in the basket seems to be very close to 100%. I would have expected the water level to drop at least a little and potentially break the vacuum in the basket with enough loss. There is no signs of that anywhere.

Also, would love to know what will happen in the pump loses prime in the middle of a long cycle. I know it primes itself on startup (with the feature enabled), but will it prime on-demand as well?

 

[thenateo]

Just an update after a few days of testing. I've noticed at the 750 rpm speed, the water level will drop from full but will eventually settle at a level around the top of the inlet pipe. If I then let the system sit at power-off overnight at that final settle point, when starting the pump the following morning at around 12 hours later, there is no priming process... the pump gets full flow within a second or so. It sure feels unlikely there is a leak given these symptoms. It seems like this might just be a byproduct of the variable speed pump.

 

[mknauss]

Variable speed pumps will build air in the pump basket when run at very low rpms. Try running your VS pump no lower than 1100-1200 rpms.

 

[thenateo]

That's consistent with what I'm seeing.

Right now, my pump runs from 7am - 6pm at the 750rpm speed and then at 1100rpm from 6pm - 10pm (while the Intellichlor 40 runs - since it shows a low flow error below 1000rpm). During the 4 hour run at the higher speed, the water level builds back up to near the top of the basket.

Will it harm anything to run it this way day after day? The lower water doesn't seem to cause the pump to lose prime and during the higher rpm, the water level looks close to full. I'd rather not run any higher than needed to save power, but I don't want to damage anything either.

Thanks.

 

[mknauss]

No it should not harm anything. The pump is less efficient at the very low rpm. You are moving less water per watt than at 1100 rpm.