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Thread: Do I even need a main drain?

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    Do I even need a main drain?

    Ok so in the next couple months I'll be building my own 20x40 liner type IG pool.... It would save me time, money, effort not to plumb a main drain (or 2).... I mean how often do you use that anyway? This is my first pool so I'm not sure?? But my idea would be to just use a submersible pump to pump the water out if/when I need to drain it.... Just a thought.... Any info is appreciated...
    20x40 vinyl liner IG pool, 20x16 shallow end, deep end is 8ft....Metal walls... 1hp single speed Pentair Pump..... 24" sand filter... build in progress....

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    Re: Do I even need a main drain?

    I am looking forward to mine for just moving water down low.

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    Re: Do I even need a main drain?

    By moving water you mean it's constantly sucking water through the filter like the skimmer?? Or will you just be able to turn it on once in a while to move water?
    20x40 vinyl liner IG pool, 20x16 shallow end, deep end is 8ft....Metal walls... 1hp single speed Pentair Pump..... 24" sand filter... build in progress....

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    mas985's Avatar
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    Re: Do I even need a main drain?

    This is one subject that certainly does not lack for coverage:

    do-i-even-need-a-main-drain-t40077.html
    deep-end-main-drain-vs-downward-pointing-return-t39071.html
    should-i-go-with-pool-without-main-drain-t38222.html
    to-main-drain-or-not-to-main-drain-t33788.html
    main-drain-t24929.html
    main-drain-t23533.html

    As you can tell, I am clearly in the "don't need" camp although I do have one in my pool. But I wouldn't really miss it much if I didn't have and if I ever build another pool, I will probably skip the main drain.

    They do nothing for cleaning and/or circulation that can't be done by other things.

    For circulation, a lower return or even a return pointed downwards does far more for circulation than a main drain. Main drains these days are designed to keep the water velocity as low possible so they will draw water from near the drain and above it but that is about it. Where as a return can have very high exit velocity and affect the entire pool.

    For cleaning, an automatic cleaner will do far more for cleaning than a main drain. Again because of the low entrance velocity, they will not attract bottom dirt beyond a few inches of the drain.

    They may be useful for draining the pool with the main pump, but most pumps will start drawing in air as the water level drops so even that is not enough reason to go with a main drain.

    Also, if you have problems with the main drain plumbing, they are much more difficult to fix than a side return or skimmer plumbing which can be reached with a little digging.
    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: Do I even need a main drain?

    They say to add another suction line in the side of the pool if you get rid of the drain.... What's that all about? That seems more dangerous to have a suction in the side wall rather than all the way at the bottom.... And also some say it messes with the pump if you don't have a main drain..... I'm leaning to the no main drain side, but I just want to be sure before I skip it!
    20x40 vinyl liner IG pool, 20x16 shallow end, deep end is 8ft....Metal walls... 1hp single speed Pentair Pump..... 24" sand filter... build in progress....

  6. Back To Top    #6

    Re: Do I even need a main drain?

    My pool in NJ has a skimmer and main drain and I find the main drain helps tremendously with small debris and small items that fall to the bottom. Having 2 goldens, it does a great job of collecting the hair in one spot, which I manually pull out.

    The pool in FL has 2 main drains and collects the debris from the in floor cleaning system (also collects sand that blows in from around the pool - from the pavers).

    My vote is go for the main drain.
    Julie
    I have a small (3,750 gallon) in-ground, Viking pool - 2hp Jandy pump, AquaPure 700 Cholorinator, Jandy Aqualink, and Jandy CJ250 filter

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    mas985's Avatar
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    Re: Do I even need a main drain?

    Quote Originally Posted by WhoDat?
    They say to add another suction line in the side of the pool if you get rid of the drain.... What's that all about? That seems more dangerous to have a suction in the side wall rather than all the way at the bottom.... And also some say it messes with the pump if you don't have a main drain..... I'm leaning to the no main drain side, but I just want to be sure before I skip it!
    That is for the rare situation where the water level might drop below the skimmer and to protect the pump they will plumb a suction line below the skimmer at a lower depth into the second port of the skimmer. A valve is used so that this suction line is normally closed but when the level of the water drops, a float in the skimmer seals the skimmer path and then the valve in the bottom of the skimmer releases so that water can be drawn in from the lower point. This isn't really needed if you have an autofill but some people like the idea of extra protection. As for safety, it can be plumbed fairly low and out of the way and they use the anti-entrapment covers and can also be plumbed into pair so that shouldn't be an issue. Plus, they aren't normally activated unless you want that. The following link shows how this is usually plumbed:

    Skimmer Equalizer


    I don't remember if I posted this link before, but the APSP did a case study on main drains and came to the conclusion, that they were not really necessary:

    APSP Case Study
    Pool and Spa News Article

    Also, here is a video showing how a 18"x18" main drain running at 800 GPM hardly moves the water. This is equivalent to a main drain pair running at 34 GPM.

    Main Drain Video
    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: Do I even need a main drain?

    Reading that APSP Case Study makes me think my main drain was PURPOSELY disabled when the new skimmer was put in. Makes sense to me now.

    It amazes me how clean my water stays with just one skimmer in the middle of a 44,000 gallon pool.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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  9. Back To Top    #9

    Re: Do I even need a main drain?

    Quote Originally Posted by mas985
    Quote Originally Posted by WhoDat?
    They say to add another suction line in the side of the pool if you get rid of the drain.... What's that all about? That seems more dangerous to have a suction in the side wall rather than all the way at the bottom.... And also some say it messes with the pump if you don't have a main drain..... I'm leaning to the no main drain side, but I just want to be sure before I skip it!
    That is for the rare situation where the water level might drop below the skimmer and to protect the pump they will plumb a suction line below the skimmer at a lower depth into the second port of the skimmer. A valve is used so that this suction line is normally closed but when the level of the water drops, a float in the skimmer seals the skimmer path and then the valve in the bottom of the skimmer releases so that water can be drawn in from the lower point. This isn't really needed if you have an autofill but some people like the idea of extra protection. As for safety, it can be plumbed fairly low and out of the way and they use the anti-entrapment covers and can also be plumbed into pair so that shouldn't be an issue. Plus, they aren't normally activated unless you want that. The following link shows how this is usually plumbed:

    Skimmer Equalizer


    I don't remember if I posted this link before, but the APSP did a case study on main drains and came to the conclusion, that they were not really necessary:

    APSP Case Study
    Pool and Spa News Article

    Also, here is a video showing how a 18"x18" main drain running at 800 GPM hardly moves the water. This is equivalent to a main drain pair running at 34 GPM.

    Main Drain Video
    Ok thanks!! I don't think I'll have an automatic fill line.... However I don't plan on ever winterizing it either... I'm in south Louisiana .... So I'll probably never close it.... But the idea of the lower drain isnt bad... But I like that it's not necessary.... I think it would save me time and money to just add a lower return in the deep end facing down toward the center of the deep end.... Thanks for all the replies!!! Any info is always appreciated!!
    20x40 vinyl liner IG pool, 20x16 shallow end, deep end is 8ft....Metal walls... 1hp single speed Pentair Pump..... 24" sand filter... build in progress....

  10. Back To Top    #10

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    Re: Do I even need a main drain?

    Side wall suctions are pretty SOP where I am, at least in vinyl pools. They are usually put in about 18 inches or so below the top of the pool in the deep end. Mine is plumbed on a separate line back to a 3 way valve at the pump. I did have a leak a couple of years ago and it saved me from running the pump dry. I nkow theres a big differecne of opinion, but I think it helps with circulation (not intending to start a discussion over it, but it's what I think, as well as a lot of builders). The other thing it helps with is manual vacuuming. I have a robot, but sometimes i need to manually vacuum. If you only have the skimmer, the vacumm head can get sucked down on the pool surface where you cant even move it. Letting a little suction off onto a main will really help make vacuuming a lot easier. My neighbor has only a skimmer and he curses it every day when he vacuums that he doesnt have a side wall suction.
    As far as safety goes, its not an issue. They are plumbed using 2 suctions lines, a couple a feet apart with anti entrapment safety covers. If it were mine, i'd do a side suction.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    mas985's Avatar
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    Re: Do I even need a main drain?

    bk406, you may want to check your skimmer because most installations of side wall suction ports as shown in the pentair link I posted, are normally shut off so you actually don't get any suction flow from that port unless there is a problem.

    Also, even if that suction port was normally operating, having a return in the same location as that suction port instead would provide much better 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: Do I even need a main drain?

    Quote Originally Posted by mas985
    bk406, you may want to check your skimmer because most installations of side wall suction ports as shown in the pentair link I posted, are normally shut off so you actually don't get any suction flow from that port unless there is a problem.
    It's not plumbed that way. It doesnt hook into the skimmer at all. The reason it saved me when i had a leak was that i shut the skimmer down completely during the time it took to repair the leak and still was able to operate the pool.


    Quote Originally Posted by mas985
    Also, even if that suction port was normally operating, having a return in the same location as that suction port instead would provide much better circulation.
    As I said, I'm not here to argue that point
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

  13. Back To Top    #13
    mas985's Avatar
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    Re: Do I even need a main drain?

    Quote Originally Posted by bk406
    As I said, I'm not here to argue that point
    You're no fun.
    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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