Main drains - How do they work?

ktdave

LifeTime Supporter
May 8, 2007
888
Katy, TX
In my pool, I have 2 skimmers, one of which (nearest to the pump) the dual main drain is connected to. In the bottom of this skimmer there are 2 holes, one with suction going to the pump, the other (no detectable pressure/suction) coming from the drain. I just don't see how any circulation is being created in the drain without it being somewhat of a closed system. Is this a "normal" configuration?

Thanks for any insight.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
There are a couple of different ways that main drains get plumbed. That is the slightly cheaper and less desirable way. The idea behind that setup is that if the skimmer basket gets blocked with leaves the pump will draw from the main drain. Many of the two hole skimmers also have an optional float valve that fits between the pipes on the bottom and the basket that allows the pump to draw from the main drain when the water level goes below the skimmer.
 

ktdave

LifeTime Supporter
May 8, 2007
888
Katy, TX
Thanks Jason!

It seems like I could rig a "U" joint connecting the drain to the suction line that has a ball valve in it that could regulate the amount of flow btween skimmer and drain. I just feel that if the drain is there to be utilized, why not use it to create better circulation.
 

TheOne

LifeTime Supporter
Mar 28, 2007
167
Houston, TX
Yes, ideally each skimmer and your main drain will be plumbed directly with home runs back to the equip pad. That way you can adjust circulation between main drain and skimmers.

I use valves at the equipment pad to run one of my skimmers at the larger end of my pool at about 60% with the other skimmer about 40%. Meaning I direct more suction from one skimmer than the other. Further between skimmers and main drain I pull 70% from my skimmers and 30% from my main drain.

This setup also has the benefit of changing suction to 100% from skimmers in case someone is paranoid about main drains. If I am doing heavy cleaning I can pull 100% from the main drain and turn the pump on high speed. I also have a main drain skimmer bag so I can clean it out pool side if needed.