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Thread: no suction from main drain

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    no suction from main drain

    I have not had any suction from the main drain since I moved into this house last year. Since the deep end is 10' deep it seems like my circulation will always be insufficient only pulling from the skimmer and spa. I also have a persistent fine layer of dust/sediment on the bottom of the pool. The pool guy came out a couple weeks ago to replace a valve and said I would need to buy a "hydro control plate" in order to divert flow from the skimmer and force the pump to pull from the main drain. This is the part # he wrote down: http://www.aqua-man.com/row_num.asp?Ic=12635

    Is this god practice to use the control plate to pull from the main drain while filtering, and just open the skimmer to vacuum?
    25K gal IG plaster pool w/ spillover jacuzzi, 12 Gulf Solar coils (leaking/currently bypassed), ancient Raypak propane heater (rusted/currently bypassed), Pentair 001018 VS pump, 4.9 sq ft Triton II sand filter, Taylor K-2006 FAS-DPD kit

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    mas985's Avatar
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    Re: no suction from main drain

    Even when working properly, a main drain will never really clear debris from a pool's floor more than a few inches from the main drain. IMHO, main drain's aren't very useful for anything but circulation. It is far more important for the flow rate to be concentrated in the skimmer where debris can be removed from the surface before it sinks to the pool floor.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: no suction from main drain

    I agree that it won't clear much debris but I'm not getting any circulation . Will the hydro plate let me divert 25% main drain circulation and 75% to skimming?
    25K gal IG plaster pool w/ spillover jacuzzi, 12 Gulf Solar coils (leaking/currently bypassed), ancient Raypak propane heater (rusted/currently bypassed), Pentair 001018 VS pump, 4.9 sq ft Triton II sand filter, Taylor K-2006 FAS-DPD kit

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    Re: no suction from main drain

    Quote Originally Posted by twd000
    I agree that it won't clear much debris but I'm not getting any circulation . Will the hydro plate let me divert 25% main drain circulation and 75% to skimming?
    25K gal IG plaster pool w/ spillover jacuzzi, 12 Gulf Solar coils (leaking/currently bypassed), ancient Raypak propane heater (rusted/currently bypassed), Pentair 001018 VS pump, 4.9 sq ft Triton II sand filter, Taylor K-2006 FAS-DPD kit

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    mas985's Avatar
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    Re: no suction from main drain

    How do you know you are not getting any circulation and why do you think it is important? Most pools operate just fine without a main drain.

    And yes, a diverter can draw more water from the deep end but at the expense of the skimmer so the skimmer may not work as well.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: no suction from main drain

    Quote Originally Posted by mas985
    How do you know you are not getting any circulation and why do you think it is important? Most pools operate just fine without a main drain.

    And yes, a diverter can draw more water from the deep end but at the expense of the skimmer so the skimmer may not work as well.
    I turned the pump on3500 rpm and swam down with a scuba mask. Put my hand over it and threw some leaf litter nearby and no indication of suction
    25K gal IG plaster pool w/ spillover jacuzzi, 12 Gulf Solar coils (leaking/currently bypassed), ancient Raypak propane heater (rusted/currently bypassed), Pentair 001018 VS pump, 4.9 sq ft Triton II sand filter, Taylor K-2006 FAS-DPD kit

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    mas985's Avatar
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    Re: no suction from main drain

    Newer main drains are designed to distribute the water flow in such way as to minimize the water velocity going into the drain which prevents entrapment but it also makes it very difficult to detect water movement. Did you try a dye test? That is the only way to know for sure if there is any flow rate through the drain. Even without a diverter, the main drain should still draw some water and you really don't need much water going through the main drain for circulation.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: no suction from main drain

    Quote Originally Posted by mas985
    Newer main drains are designed to distribute the water flow in such way as to minimize the water velocity going into the drain which prevents entrapment but it also makes it very difficult to detect water movement. Did you try a dye test? That is the only way to know for sure if there is any flow rate through the drain. Even without a diverter, the main drain should still draw some water and you really don't need much water going through the main drain for circulation.
    Not a newer main drain - circa 1977. Wonder if mine is designed for minimal flow? How much dye would I need to use for a dye test? Seems like I would need a lot to see it show up in the pump basket
    25K gal IG plaster pool w/ spillover jacuzzi, 12 Gulf Solar coils (leaking/currently bypassed), ancient Raypak propane heater (rusted/currently bypassed), Pentair 001018 VS pump, 4.9 sq ft Triton II sand filter, Taylor K-2006 FAS-DPD kit

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    Re: no suction from main drain

    Quote Originally Posted by twd000
    Quote Originally Posted by mas985
    Newer main drains are designed to distribute the water flow in such way as to minimize the water velocity going into the drain which prevents entrapment but it also makes it very difficult to detect water movement. Did you try a dye test? That is the only way to know for sure if there is any flow rate through the drain. Even without a diverter, the main drain should still draw some water and you really don't need much water going through the main drain for circulation.
    Not a newer main drain - circa 1977. Wonder if mine is designed for minimal flow? How much dye would I need to use for a dye test? Seems like I would need a lot to see it show up in the pump basket
    You need to put the scuba mask on again and dive down with syringe of food coloring. Squirt a little stream of it right near the drain and see if it gets sucked in.
    Bill
    18'X4' 7600 Gal AG
    3/4 HP Pentair Pump
    Hayward S166T 100 lb sand filter

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    mas985's Avatar
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    Re: no suction from main drain

    Quote Originally Posted by yeggim
    You need to put the scuba mask on again and dive down with syringe of food coloring. Squirt a little stream of it right near the drain and see if it gets sucked in.



    Also, the pool may be old but during refinishing, the main drain covers may have been replaced so it is possible to have a newer VGB compliant cover on an older pool. Are there two main drains about 3' apart or a single main drain?

    Also, sometime main drains will clog with debris so if you still don't detect any water movement with the food color test, you should try to flush the main drain backwards from the skimmer. You might even try this before the food color test.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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