pool pump dropping flow rates mystery

minivanSeptember 6, 2011

I am a long time reader and fan, first time poster. I am facing a puzzling loss of flow in the pool circulation. The setup has just the pool with solar heating. It is about 30K gallons, with an Intelliflo pump and hayward 400sqft cartridge filter.

There is a check valve right after the filter and another one right after the solar panels. There is a vacuum breaker at the top of the panels.

Normally the pressure gauge at the filter reads 8-10psi, and the flowmeter installed after the filter and checkvalve, but before the solar panels reads 50-60 gpm. Solar is engaged and operating normally, pump is at 2650rpm as programmed. System is relatively quiet.

Once in about 3 days, when I take a look, I find:

flow is down to 15-25 gpm and fluctuating.

there are bubbles in the pool where water is being returned to it.

pressure gauge on the filter reads 25-30psi.

there are gushing noises. Relatively loud, but I am not able to pinpoint where they are coming from. If I had to guess, I'd guess somewhere near the check valve that is right after the filter. The valve body is completely opaque, so can't see anything here.

the check valve after the solar panels has a clear lid, and I can see the flowing water is not filling the whole pipe and there is turbulence. All piping is 2", but normally the pipe is full of water, and no turbulence is visible here.

There is 3-6 drops per minute leaking from the inlet port of the filter.

From the bubbles, I guess, air is entering the system somewhere. But I don't understand first, why it happens only some of the times, and second, how to explain the readings of the filter pressure gauge and the flow meter.

Please help.

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poolguynj

Losing any water?

The gushing is likely air.

Is the pump surging?

Is there air in the pump?

I assume the pressure reading is with solar on to the panels.

Scott

    Bookmark   September 6, 2011 at 8:12PM
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mas985

If your panels are on the roof, 10 PSI may be enough pressure to keep the vacuum release valve closed and the panels may lose prime. Increase the RPM slightly and see if the problem goes away.

    Bookmark   September 6, 2011 at 8:27PM
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minivan

Thank you for the responses.

@poolguynj -- The pool loses about 2-3 inches per week from a 600sqft surface area. The pump is not surging. In the pump strainer basket, there is very little air -- maybe 1-2 bubbles of 1-inch or less at the top of the lid. The pressure reading is with the solar engaged.

@mas985 -- I have increased rpm to 2900. Waiting to see if it will occur again.

A few more observations:
Once the problem happens, if I then increase the rpm to 3450 (the max), the flow rate does not improve much (30gpm). Pressure gauge reading shoots up to 38-40psi. In contrast, when operating well, system moves 90-100gpm at 3450rpm.
When I open the air relief valve on the filter, there is hardly any air coming out. i.e. the filter remains full of water for the most part.
If I turn off the whole system, wait 5 minutes, and turn it back on, 50% of the time the problem disappears.
If I disengage the solar by reversing the switch on the valve actuator, while the problem was happening, the problem does not go away.
Cartridges in the filter are more than 5 year old, although I cleaned them a month back.

    Bookmark   September 7, 2011 at 12:15PM
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minivan

@mas985 -- forgot to mention before. The solar panels are on a sloping roof, 12-16 feet above.

thanks.

    Bookmark   September 7, 2011 at 1:20PM
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poolandspaguru

What is the condition of your filters in the cartridge filter? Have you tried removing the filters and running the system to see if this results in lower operting pressures? If so you may have scale on the filters if not other debris depending on how often/well you clean the filters.

They can plug from scale if your saturation index is in a potantial for scaling condition, or they can plug up from body oils, sunscreen, lotions etc and if this is the case then you need to clean the filter with a detergent cleaner. Either way running the system without the filters will let you know if this is the problem or not.

    Bookmark   September 11, 2011 at 5:43PM
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minivan

@poolandspaguru - the cartridges are very old -- more than 5 years. Without the cartridges I get 8-10psi as well. This is same as running with the cartridges when the system isn't acting up. Maaaaybe 1 psi lower..

TBH, this is a bit surprising. Could it be that one or more cartridges are torn (I can't tell, at least visually..)?

    Bookmark   September 12, 2011 at 4:51PM
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