Basic question re: Main Drain

[pmaroun]

Still a new pool owner that is learning every day..

I have a main drain in the bottom of my pool. It and the two skimmers each have separate pipe coming in to the pump.

My front skimmer pulls pretty hard.. My back skimmer (deep end) not so much. However, I have never felt any pull coming from the main drain. All three lines coming in have valves in the open position.

Is something wrong with my main drain? Should it always be pulling? If so, what steps should I take.

Thanks!

 

[Divin Dave]

Hi Pete,
what you are experiencing is pretty much normal. The main drain is several feet lower than the pump level, right? That means the pump has to suck water up hill to get it to the pump. Not the case with the skimmers. So its gonna take more suction from the pump to pull that water uphill.

If you want to suck water from the main drain more, then you will have to close the valve to one of the skimmers. Or at least throttle it down a bit. Every valve you close, will increase the flow from all of the others that are open.

 

[Yev]

Do you have 1 main drain or 2? Most states require 2 main drains on new pools, which eliminates any chance of drowning caused by getting "sucked into" the main drain. If you try to block one to feel the pull, the other one will send all the water back to the pump.

Some more experienced people here will be able to give you a more technical answer, but I think that you will prefer that the skimmers provide most of the water going out to the pump, as this will allow for more debris to get trapped. As for the main drains, they serve a small purpose from what I know. Without main drains, in the deep end of a pool you can end up with a different chemistry that at the surface, so the main drain helps to insure a more consistent mixture. Plus the main drains help with even temperature profile at depth.

 

[pmaroun]

I have one main drain. It is quite a bit lower than my pump (approx. 9 feet lower). There is absolutely no suction that I can feel coming from it. However, when I try to pull prime from my pump, I pull from the Main drain first, then from the skimmers--so the Main drain is pulling when the skimmers are off.

So, what is the purpose of my main drain if it is not pulling while the skimmers are pulling?

 

[pooldv]

Is the main drain shut off with a valve? If the valve is open the there is still water flowing. Water flow plus gravity will pull debris off the bottom.

 

[Divin Dave]

Over a century ago before there were pumps and sanitizers the main drains were acutally that. For Draining. Thats why it is called a drain. Fast forward to the 60's, the prevailing though was the a main drain is needed to increase circulation and thought thought is still held by old timers.

FF til today with better pumps etc, and there really isn't any pressing reason to have a main drain. Many pools are built without them these days. Including mine.

If you wanna know if it acutally works or not, open both skimmers and the main drain and make sure water is flowing through the pump and you can see it through the lid,
then turn the valves to both skimmers off. If water keeps flowing then its pulling from teh MD. If not, well...then its not.

I have one main drain. It is quite a bit lower than my pump (approx. 9 feet lower). There is absolutely no suction that I can feel coming from it. However, when I try to pull prime from my pump, I pull from the Main drain first, then from the skimmers--so the Main drain is pulling when the skimmers are off.

So, what is the purpose of my main drain if it is not pulling while the skimmers are pulling?