Question about bottom outlet

Lord Uhtred

Member
Jul 20, 2021
6
Montreal, Quebec
I recently had a 12x28' fiberglass pool installed, with a saltwater system. There is an outlet on the side of the pool, at the bottom, with a pipe running to the skimmer (which is on the same side). It's about 2" inside diameter. However, there is almost no flow through this pipe. If I shut the skimmer door, rather than increasing the draw through the pipe, it drains the skimmer. Does anyone else have this kind of design and is it normal that only like 2% of the suction is going through the outlet at the bottom, and the rest coming from the surface? I'm attaching photos.
 

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Texas Splash

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That appears to be an equalizer line. Those can go either to the skimmer or drain (if installed), so you want to be sure how yours is plumbed. It's a supplemental source of suction if your water level ever gets too low in the skimmer or the drain gets plugged. If it does connect to the skimmer, you probably won't see much suction from it as the first skimmer hole will pull most of the water directly from the skimmer for the pump. For 2-hole skimmers, normally the hole closest to the pad goes to the pump, and the hole facing the pool goes to the equalizer, is shared to a main drain, or is just plugged if not used (another possibility). So you might need to confirm the plumbing with your installer unless you are sure and/or have pics to confirm.
 

BenB

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Jul 24, 2020
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Yes it's normal and indeed preferred since you'll get best skimming performance that way.

Do you have a 'dome' shaped piece that sits over the top of those pipes? That is a diverter valve and what happens is if your skimmer drains down, a plastic cap falls into place preventing the pump from sucking in air from the empty skimmer above, and in turn this forces water to be sucked up through the other pipe i.e. from the bottom of the pool.

If you don't have one, consider getting one just in case.
 

Lord Uhtred

Member
Jul 20, 2021
6
Montreal, Quebec
That appears to be an equalizer line. Those can go either to the skimmer or drain (if installed), so you want to be sure how yours is plumbed. It's a supplemental source of suction if your water level ever gets too low in the skimmer or the drain gets plugged. If it does connect to the skimmer, you probably won't see much suction from it as the first skimmer hole will pull most of the water directly from the skimmer for the pump. For 2-hole skimmers, normally the hole closest to the pad goes to the pump, and the hole facing the pool goes to the equalizer, is shared to a main drain, or is just plugged if not used (another possibility). So you might need to confirm the plumbing with your installer unless you are sure and/or have pics to confirm.
Excellent, thank you.
 

Lord Uhtred

Member
Jul 20, 2021
6
Montreal, Quebec
Yes it's normal and indeed preferred since you'll get best skimming performance that way.

Do you have a 'dome' shaped piece that sits over the top of those pipes? That is a diverter valve and what happens is if your skimmer drains down, a plastic cap falls into place preventing the pump from sucking in air from the empty skimmer above, and in turn this forces water to be sucked up through the other pipe i.e. from the bottom of the pool.

If you don't have one, consider getting one just in case.
OK this makes perfect sense. Thank you for the explanation. However, just curious, why is it when I shut the skimmer door, that doing so didn't serve to function like the "dome shaped" piece? Instead of drawing from the equalizer line, it rapidly emptied of water instead, and I had to release the door to prevent air from getting sucked in.
 

Texas Splash

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Instead of drawing from the equalizer line, it rapidly emptied of water instead, and I had to release the door to prevent air from getting sucked in.
I suspect that while one hole goes to your pump back at the pad, the other may not be used. It may just be capped off. That would explain why the pump sucks the skimmer area dry when you shut it closed. Your equalizer line might be plumbed to the drain line which is could be separate. Do you have separate skimmer and main drain lines at the pad, or a 3-wat valve controlling them? Maybe post a pic of your equipment pad if you aren't sure.
 

proavia

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If that line is plumbed to the bottom drain or equilizer line via the second hole in the skimmer, it will not pull water into the skimmer and back to the equipment if there is no functioning diverter valve in place.
 

BenB

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Jul 24, 2020
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San Jose, CA
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OK this makes perfect sense. Thank you for the explanation. However, just curious, why is it when I shut the skimmer door, that doing so didn't serve to function like the "dome shaped" piece? Instead of drawing from the equalizer line, it rapidly emptied of water instead, and I had to release the door to prevent air from getting sucked in.
Because that's not how water or suction behaves :) The line is pulling on 'everything' and it will pull on the easiest thing it can find which once all the water is gone is air. There's nothing about the water/air barrier that would make the pipe say 'oops not supposed to be sucking on air best just currrrrrve around into this adjacent hose here' - or at least not fast enough for the speed at which water is being sucked up. That's what the diverter valve does - it physically falls down once there's no water for it to float on, and because it's sealed there's then no air it can suck on, so the pressure remains and that in turn draws water up the other pipe - it effectively connects the two pieces of pipe by making a seal around them.

TS could also be right that the pipe might not even go anywhere in which case a diverter wouldn't help either and you'd be creating a vacuum and would damage your pump.
 
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Lord Uhtred

Member
Jul 20, 2021
6
Montreal, Quebec
Because that's not how water or suction behaves :) The line is pulling on 'everything' and it will pull on the easiest thing it can find which once all the water is gone is air. There's nothing about the water/air barrier that would make the pipe say 'oops not supposed to be sucking on air best just currrrrrve around into this adjacent hose here' - or at least not fast enough for the speed at which water is being sucked up. That's what the diverter valve does - it physically falls down once there's no water for it to float on, and because it's sealed there's then no air it can suck on, so the pressure remains and that in turn draws water up the other pipe - it effectively connects the two pieces of pipe by making a seal around them.

TS could also be right that the pipe might not even go anywhere in which case a diverter wouldn't help either and you'd be creating a vacuum and would damage your pump.
Wait. Did I just get schooled on hydrodynamics and taken back to university in 1993? Fair enough, all of this makes sense, and it seems to me (perhaps naively) that employing a diverter valve might also be a way to assist in cleaning the bottom with a broom instead of a vacuum?
 
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