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Thread: Is the Main Drain supposed to be an intake?

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    bbrock's Avatar
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    Is the Main Drain supposed to be an intake?

    We are shopping for estimates on having our pool resurfaced. Some of the pool contractors have stated that the main drain needs to be in compliance with VGB. But, these estimates include this as an optional item. Is the MD required to be in compliance with VGB and have a split MD?

    I swam yesterday and dove down to the MD and it was not pulling in any water when my pump was on. So that got me thinking is it supposed to pull in water? Could there be something wrong? If not, and it is not intended to be an intake for our pool, then I could save the $ by not having the MD split.

    My intake is in the skimmer. There are two holes. One pulls in water and the other doesn't (not sure what it is supposed to do).

    Any input would be great. Thanks.

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    mas985's Avatar
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    Re: Is the Main Drain supposed to be an intake?

    Yes a MD is usually on the suction side of the pump so it should be drawing water in. Sometimes they are plumbed in with the skimmer which is probably your case. Do you have a float in the skimmer? Without restricting the skimmer some, there is will be little flow rate from the main drain. But you really don't need the main drain either.

    As for VGB, I think it is optional for residential pool owners with existing pools. All new pools require compliance but older pools do not. You can also use SVRS system instead of a split drain if you want to go that direction.
    Mark
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    Re: Is the Main Drain supposed to be an intake?

    I would check on the compliance for the main drain. Check with you local home inspector. I know he in Kentucky the only people that have to be VGB compliant are commercial propertys.
    Also there are VGB compliant drain covers that can go over the existing drain.
    You probably wouldn't fill any suction at drain cause your skimmers were running I'm assuming. Try turning your skimmers off if that's possible and see if water continues to circulate. That would tell you if your drain even works

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    Richard320's Avatar
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    Re: Is the Main Drain supposed to be an intake?

    It's not drawing water because you're probably missing the diverter. Look for something like this layying around


    There's a sliding flap underneath. Closed, all the suction goes to the main drain. Wide open (or missing) it's all suction. Somewhere in between regulates how much flow to each.

    Not sure of the legalities about the drains.
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    bbrock's Avatar
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    Re: Is the Main Drain supposed to be an intake?

    Tx u all.

    I have the diverter, but no flap underneath. Do I need the flap? What would it accomplish if I had the diverter flap?

    I didn't think the main drain or anything would pull in water if the pump is off. If I have the pump off I assume the MD will still pull in water. Will have to dive in when have a chance.

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    mas985's Avatar
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    Re: Is the Main Drain supposed to be an intake?

    If you have a diverter even with no flap, the main drain will draw water, just not a lot. It is fine that way. You really don't need a main drain and it just takes away flow rate from the skimmer anyway which is much more important.

    Also, the main drain will not draw water with the pump off. It is no different than any other part of the plumbing.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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    JasonLion's Avatar
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    Re: Is the Main Drain supposed to be an intake?

    With modern anti-entrapment drain designs it is often difficult to tell that the main drain is drawing water even when it is.
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