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Thread: Filter contents backflowing into skimmer/out through drain

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    Filter contents backflowing into skimmer/out through drain

    The contents of my filter seems to be backflowing through to my skimmer and out through my drain when the pump turns off. Does the multiport valve have a backflow control? There is always a little bit of water in my waste drain pipe so I think there could be a leak there none-the-less. If it's damaged, can I open it and replace the parts without tearing up all the PVC?

    If a backflow leak is suspected, is there any means to test that aspect of my system?

    I have a Nautilus FNS filter, and the main multiport valve was made by praher in Canada.

    Thank you, thank you very much.
    15,300 gal., AG, sand filter, 1HP 2 speed pump, 40 GPM.

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    Mod Squad JohnT's Avatar
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    Re: Filter contents backflowing into skimmer/out through drain

    Welcome to TFP!

    Is your filter much higher than the surface of the water, or do you have any elevated runs like solar heat or a water feature? Do you have air in the pump strainer basket or bubbles in the returns while the pump is running?
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    Re: Filter contents backflowing into skimmer/out through drain

    The pump is is not much higher than the water level, maybe 18" tops, add another 6" for the multiport valve itself. I have no air leaks at all. I'm thinking the multiport valve is not working properly; it's 10 years old so maybe some pieces need to be replaced?

    I do have a spa that's connected to the system. There is always positive pressure in the spa return line to keep it full. When the system shuts off, the spa level drops and I'm assuming the water backflows into the pool through the multiport valve. Maybe it's taking some of the filter contents with it?
    15,300 gal., AG, sand filter, 1HP 2 speed pump, 40 GPM.

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    Mod Squad JohnT's Avatar
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    Re: Filter contents backflowing into skimmer/out through drain

    Quote Originally Posted by fletcher_101
    I do have a spa that's connected to the system. There is always positive pressure in the spa return line to keep it full. When the system shuts off, the spa level drops and I'm assuming the water backflows into the pool through the multiport valve. Maybe it's taking some of the filter contents with it?
    Almost certainly. There should be a check-valve in that line.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    Re: Filter contents backflowing into skimmer/out through drain

    Thanks for the help.

    As to the spa, there is a check valve and I've removed and capped the lines. I'm still wondering about the Praher multiport valve because I can see some DE in the pump, which means it had to of come through the multiport valve.

    Do you know if it has a backflow stop? I've looked online for a diagram but no luck.
    15,300 gal., AG, sand filter, 1HP 2 speed pump, 40 GPM.

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    Mod Squad JohnT's Avatar
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    Re: Filter contents backflowing into skimmer/out through drain

    Quote Originally Posted by fletcher_101
    Thanks for the help.

    As to the spa, there is a check valve and I've removed and capped the lines. I'm still wondering about the Praher multiport valve because I can see some DE in the pump, which means it had to of come through the multiport valve.

    Do you know if it has a backflow stop? I've looked online for a diagram but no luck.
    The multiport is a very simple valve and has no directional control. Water will flow through it from either direction.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    Re: Filter contents backflowing into skimmer/out through drain

    Hey, Fletcher,

    JohnT has got it right, I think. It certainly sounds like there needs to be a check valve in the spa line to prevent the spa from draining. The multi-port has no such valve.

    Actually, it seems to me that, with your setup, the filter and pump would drain all the way back to the pool as well...leaving the pump strainer basket with air in it and not water. Even if that's the case, the contents of the filter should remain within the filter.

    Do you have a pic that shows all your piping and equipment?
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Mod Squad JohnT's Avatar
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    Re: Filter contents backflowing into skimmer/out through drain

    Quote Originally Posted by fletcher_101
    As to the spa, there is a check valve and I've removed and capped the lines.
    If you have a capped line, that could be an issue. It may be filled with air, which compresses during pump operation. When you shut the pump off, the air expands and forces the water in the rest of the system away from it, which may be through the multiport.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    Re: Filter contents backflowing into skimmer/out through drain

    The lines were capped to test the integrity of my Jandy valves; none were leaking and I've put them back to normal.

    The spa is definately backflowing into the pool through the spa return ports. I just need to figure out how to stop the water from pushing back through the filter, the multiport, the pump, and the pool main drain. It's always done it since I've I've been in the house, but it never seemed to be taking DE with it. The filter array is new and is working.

    Can I put a check valve on the spa return line and still have the full force of the pump/filter flowing through it to the spa without affecting my overall water pressure/output? Do they make check valves that robust?

    Thanks in advance for the advice.
    15,300 gal., AG, sand filter, 1HP 2 speed pump, 40 GPM.

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    JasonLion's Avatar
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    Re: Filter contents backflowing into skimmer/out through drain

    Yes, use a check valve. Any of the better quality check valves will be fine. I suggest a Jandy check valve.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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