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Thread: Flow rate decreases within a few minutes

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    Flow rate decreases within a few minutes

    Short Story
    Turn on pump without pool cleaner - runs fine
    Turn on pump with pool cleaner (automatic (HugBug) or manual) - water flow slows down after a few minutes, to less than a quarter
    Unplug pool cleaner while pump is still running - water flow remains slow
    Switch off pump for a few seconds and switch on again without pool cleaner - runs fine (although initially it blows out a cloud of green algae that the pool cleaner just picked up off the bottom of the pool)

    What's going on here?

    Long Story
    The outlet was spitting out bubbles for quite a while, and the water flow would slow down, I thought, as a result.
    One day the pump was making a lot of noise and I found it wasn't moving any water. It seemed too much air had got in. The water inside the pump housing was steaming hot.
    I got a pool repair company to come in and they replaced a right angled pipe that was cracked that attached to the inlet of the pump housing. It worked better but there were still bubbles.
    It got progressively worse again, so I thought I would give it a go and try find were it was sucking in air. I found another cracked joint underneath the pool pump which I replaced. No more bubbles. I assumed this would also fix the water flow problem, but it didn't.

    The pump is almost 30 years old so I thought it might be the problem. I took it in to the manufacturer. They tested it out and said it was still ok, but replaced the bearings as there were a bit rusted. They also replaced the impeller as it had worn down slightly and replaced the water diffuser (I think it's called) as it had cracked.
    I reattached the pump and it did seem to run better that it did before, but after running it with the pool cleaner for a while the water flow slowed right down again. There was a lot of debris on the bottom of the pool though as the pump had now been disconnected for a quite a few weeks.
    I subsequently cleaned out as much as possible and backwashed and rinsed several times. But still the water flow rate goes right down after a while if I have the pool cleaner connected.

    It runs fine if i disconnect the pool cleaner. It also runs fine if I bypass the filter and connect the pool cleaner - but then it just circulates the dirt.

    It seems a bit of fine debris picked up off the bottom of the pool by the pool cleaner that makes it's way to the filter substantially decreases the flow rate, but a bunch of leaves trapped in the weir basket doesn't.

    Also, once I disconnect the pool cleaner, switch off the pump for a few seconds and then back on again, it runs fine. If the flow rate remained low then I would suspect a faulty pump, but this just blows my mind. Also, when i switch it back on, it blows out a cloud of green algae (the stuff that it just picked up off the bottom)

    Still, the only thing I can think of is a faulty pump as it's so old, but i don't want to fork out more money on a new pump having already had it repaired, if I don't know for sure it's the pump at fault.

    Any ideas?

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    duraleigh's Avatar
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    Re: Flow rate decreases within a few minutes

    I may be missing something but it sounds like your filter is clogged badly.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Mod Squad Bama Rambler's Avatar
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    Re: Flow rate decreases within a few minutes

    Quote Originally Posted by fogeshan
    Switch off pump for a few seconds and switch on again without pool cleaner - runs fine (although initially it blows out a cloud of green algae that the pool cleaner just picked up off the bottom of the pool)

    What's going on here?

    Any ideas?
    See bold underlined words. There's your problem. The algae that the vacuum is picking up is clogging the filter and reducing the flow. It also sounds like the filter is bypassing some of the algae.

    What's your filter pressure before vacuuming and after vacuuming?
    What filter do you have?
    Are you cleaning the filter after vacuuming?
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: Flow rate decreases within a few minutes

    Can you vac to waste so the algae doesn't get to the filter, until youre clean again?
    26' X 52" Intex Ultra Frame. Intex Sand Filter
    26' X 52 Intex Ultra Frame Install
    You can lead a horse to (clear) water, but you can't force him to swim in it!

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    Re: Flow rate decreases within a few minutes

    Quote Originally Posted by duraleigh
    I may be missing something but it sounds like your filter is clogged badly.
    It's the one thing I haven't checked as i replaced the sand about 6 months ago. Will open it up and have a look.

    Quote Originally Posted by Bama Rambler
    See bold underlined words. There's your problem. The algae that the vacuum is picking up is clogging the filter and reducing the flow. It also sounds like the filter is bypassing some of the algae.

    What's your filter pressure before vacuuming and after vacuuming?
    What filter do you have?
    Are you cleaning the filter after vacuuming?
    Maybe its a combination of too much debris and an old pump.

    No idea about the pressure - the gauge has been broken.. in fact i don't recall it ever working. You can definately feel a difference in the flow at the outlet though.

    It's a sand filter. It takes 3 bags (assuming a "bag" is a standard unit of measure for pool filters )

    Yip, backwash and rinse.

    Quote Originally Posted by PAGirl
    Can you vac to waste so the algae doesn't get to the filter, until youre clean again?
    I started with that, but the water level goes down really quick, so i switched back to the filter.


    It seems the best cure though is posting about the problem on a pool related forum - the pool cleaner ran for several hours today until i switched it off - it hasn't done that in a while.

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    UnderWaterVanya's Avatar
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    Re: Flow rate decreases within a few minutes

    Quote Originally Posted by fogeshan
    It seems the best cure though is posting about the problem on a pool related forum - the pool cleaner ran for several hours today until i switched it off - it hasn't done that in a while.
    I nearly laughed out loud reading this... Been there. Not with the same problem, but I understand the frustration.



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    Re: Flow rate decreases within a few minutes

    Yes, it's a well known fact that posting on TFP raises your pool karma immediately. Note the posting frequency of many of the contributors here.
    38K in ground pool with attached spa. Current equipment: Easytouch 8 (521150) with IC-60 SWCG with web control by Autelis, 1x Pentair IntelliFlo 011018 pump (for filter), 1x Pentair 2HP WhisperFlo pump (for waterfall), 2X Pentair IntelliBrite 5G 12V lights, Pentair MiniMax400 NG Heater, Pentair SMBW2060 DE filter. Zodiac Barracuda MX8 cleaner on dedicated cleaner line. Lighting/home automation controlled by Insteon/ISY-99i.

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