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Thread: Main drains...is there supposed to be a lot of suction?

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    Rockadile's Avatar
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    Main drains...is there supposed to be a lot of suction?

    My newly built pool was filled last week and I have been brushing twice daily for 6 days now and there seems to be no reduction in the amount of dust being kicked up. Is this normal? During my indoctrination, I was shown how to divert all of the suction to the 2 main drains in the deep end. This was 3 days ago. I find it interesting to brush at night with the light on so I can see how much plaster dust is getting kicked up while I brush. Unfortunately, when I was brushing the dust toward the main drains, I didn't see it getting sucked in like I expected. The next day, I took a swim with the suction diverted to the main drain and swam down and held my hand over it. I didn't feel a lot of suction. Am I expecting too much or is this not normal. Is there a way to test if the suction is too low?

    Thanks.
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    Re: Main drains...is there supposed to be a lot of suction?

    You're like 3 inches from me, wow. Anyway, the 2 main drains are really one main drain. Be very careful the main drain is very dangerous and you can become trapped at the bottom of the pool and drown. That's why there are 2 drains to help prevent you from killing yourself. It's really one drain connected to both covers that way you would have to be over both covers in order to stick to the bottom. There is true stories of children trying to sit on the main drain and having their lower intestine sucked out of their body. It's gruesome but you really need to be careful. Most people I know actually turn off their main drain while anyone is in the pool as a safety precaution.

    To put it simple, I have the two main drain setup myself and even when I divert all suction to the main drain I really don't see much visual suction on any dirt down there. I honestly think that's by design.

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    Rockadile's Avatar
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    Re: Main drains...is there supposed to be a lot of suction?

    I have a hard time believing that you would have that much suction, and not notice it sucking in the plaster dust. Even if the suction was only enough to hold an infant down (I know...kinda morbid...mine wouldn't hold much more than a piece of paper, I would guess), I would think you would see it sucking in the dust. Maybe I'm wrong, but I just don't see it.
    Equipment, etc.
    30,000g IG Quartz
    Goldline Aqua Logic SWG
    Hayward SwimClear Cartridge Filter
    AquaComfort Heat Pump
    Hayward Phantom Turbo Cleaner
    Taylor K-2006 & K-1766
    Procrastination is the key to flexibility.

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    Re: Main drains...is there supposed to be a lot of suction?

    Quote Originally Posted by piku

    To put it simple, I have the two main drain setup myself and even when I divert all suction to the main drain I really don't see much visual suction on any dirt down there. I honestly think that's by design.
    This is correct. Also main drains also have anti vortex grilles on them that also seem to diminish the suction. If you have any doubts as to whether the drains are working just turn off your skimmers and see if there is a difference in flow from your returns. There shouldn't be.

    There can be a LOT of plaster dust when starting a new pool.

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    mas985's Avatar
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    Re: Main drains...is there supposed to be a lot of suction?

    The flow into the anti vortex drains can be deceiving. They distribute the flow rate around the drain and between the two drains so it is very difficult to actually see the flow into the drain.

    Also, depending on the size of pipe the plumber used to the main drain, main drains will typically have less flow rate than the skimmers. Another way to check if there is an issue is to compare the filter PSIs when you have everything on and then just the main drains. The pressure shouild drop some with just the main drain but not a lot. If there is a significant drop in pressure with just the main drain, then there could be a problem.

    It is likely that it just difficult to see the dust flowing into the drains. Also, 6 days is not unusual to still see dust. I think I remember seeing it for a couple of weeks.
    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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    Rockadile's Avatar
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    Re: Main drains...is there supposed to be a lot of suction?

    Thanks guys. This is good to know. When I do switch the skimmers off, the pressure does drop a little and I do see abit of air coming out the returns, but I assuming this is normal.
    Equipment, etc.
    30,000g IG Quartz
    Goldline Aqua Logic SWG
    Hayward SwimClear Cartridge Filter
    AquaComfort Heat Pump
    Hayward Phantom Turbo Cleaner
    Taylor K-2006 & K-1766
    Procrastination is the key to flexibility.

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