My feedback on main drains in an above ground pool...

[DennisP]

Hey guys, I figured since I have had a pool for a few months now and since it is now winterized, it was time to give my feedback in regards to main-drains in an above ground pool.

I know there is tons of people saying, "Don't do it!", but I ignored them all and did it anyways.

As a result I have found all the following major plusses:

- Increased circulation within the pool
- Collection of debris at the bottom near the drains
- I always have circulation, regardless of how "full" the skimmer gets (I have them both cut in full at the pump)
- Draining of the pool (excess water from rain, or draining to winterize) is easy

Now, I also have dual returns (one near the skimmer, like everyone else, and another I installed directly across the pool from the original one) and I have played quite a bit with the valving I installed to run on skimmer/one return like most above ground pools have, as well as combinations of all sorts (main drains only, both returns equal, skimmer only, etc) and as well as using my pool heater quite a bit (the kids were swimming in 45 degree weather for a few weeks).

I can say that the main drains are more of a necessity more than a "really don't need" kind of item. in heating the pool without the main drains the bottom was always cooler (and yes, I tried aiming the returns, using a single to "stir more" with a stronger stream, etc) and without dual returns you always had a "dumping spot" for debris to end up (which meant more vacuuming). I also found that without main drains, if the skimmer got full it would choke off the pump and returns. That just doesn't happen with the main drains also being cut in.

I will say, the skimmer works best without the main drains being cut in, but that is also dependent on a single return being used (seemed to force the largest amount of floating garbage to the outside quicker).

But, with both returns, the main drain and the skimmer all operating full, the pool had the best circulation, the surface always stayed clear, the garbage collected near the main drains as much as possible (which means vacuuming was kept to minimum, since all you do it shut off the skimmer and the main drains sucked in as much as possible) and in general the pool was as low-maintenance as possible.

Now, I will admit, my setup is pretty stout, in that I have 2" piping from the skimmer as well as 2" piping at the main drains (dual main drains, connected via 2" and tee'd to 2") with all 2" lines for the suction and the return side (I did use 1.5" line to go to the second return, but it was 2" up until it tee'd off). I used a Pentair Dynamo 1.5hp dual speed pump and ran it on low for 10 hours a day and on high for two shifts of two hours each, so 10 hours on low and 4 hours on high. I have timers for pump actuation as well as low/high modes (with a firemans switch on the high mode) as well as a manual override built into the pump that allows me to switch to high-mode and activate the firemans relay so I can command heat for longer periods off-timer. I need to figure out a way of adding another relay so that I can just set the pump to low-mode and if heat is needed it will kick the pump to high-mode when the heat turns on. I know I can do that with an external automation system, but I am trying to avoid that for now.

The main drains are also installed with a 50lb bag of fast-setting concrete used as a base for the drains as well as encasing the tee'd section in concrete as well to make sure no-one can move anything.

My advice to anyone considering a main drain setup, go for it. You won't regret it and entrapment isn't an issue with the dual-drain setups they sell today. Yes, you have those that complain it is just another possible leak, but really it all comes down to assembling it properly. I would also argue that those that have leaks at skimmers/returns and main drains are probably in need of a new liner anyways. Good time to use new gaskets everywhere and make sure the pool itself is in good shape. Nothing is built to last forever, and a set of main drains is not going to accelerate how quickly things need to be replaced.

[FormerBromineUser]

Very interesting! I have an in-ground with a main drain and often switch off/on the skimmer and main drain valves depending on what I'm doing also. Very handy. I would agree that DIY'ers would find benefit to adding a main drain.

[JimK]

Agreed.

[hrsdennis]

Hey Dennis, Dennis here. While I agree with most everything you said, I still say no main drain, in the majority of above ground pool installations.

You have no idea how many times I have heard, "my pool is leaking, I think it's my main drain." It seldom is but always the first place suspected. That is if it is properly installed, if not, then it probably always is the cause. Thing is, there is no way of knowing.

Automatic pool cleaners do exactly the same thing, they draw water from the bottom, plus they clean the entire pool floor. They replace the need for a center drain.

There is a lot that can be done with an above ground pool, huge filter systems, multiple returns, main drains, dedicated cleaner ports and so on. It's all good if done right and maintained. But if you are at the mercy of others when it comes to keeping all this stuff working, you may want to keep it simple.

[DennisP]

Thanks for the reply Dennis.

And, from your perspective, being a pool installation professional, I can understand your motivations to keep the "common owners" from going with a main drain.

I am far from a "common owner", and I have noticed that a large number of those on the web posting about pools seem to be those are are far removed from being engineering types, handyman types and/or those with mechanical proficiency.

So, as you said, for the majority of people, no main drain is common sense. But, for those of us "with a clue and ability" a main drain is essential.

Without a main drain winterizing is a PITA. Without a main drain you can't circulate water while heating a pool and melting the ice the formed over winter for an early spring opening (which I did this year, which required using only the main drain to pull water out, circulate it through the heater and then send heated water back to the pool while also allowing me to fill the pool with my dedicated fill bib and line setup)... My kids were swimming the first week of March when we hit 70 degrees for a day or two. Without a main drain that would have been impossible as I would have had to fill the pool first to use the skimmer, then I would have had the issue of ice shards plugging the skimmer (which would have prevented flow through the system to use the heater)...

I just want to be sure that those that are true DIY types that are extremely detail oriented seriously consider a main drain setup for it's many advantages. Those hiring others to do everything need not consider it.

[hrsdennis]

Great post Dennis, no argument here. It is more of an advanced thing, but more than worth it in many cases. Enjoy the "long" summer with your kids. I raised four daughters in Arizona, never short of swimming season, and we always had a pool to enjoy together.

Dennis

[Anonymous [GDPR] European in the UK]

As a result I have found all the following major plusses:

- Increased circulation within the pool
- Collection of debris at the bottom near the drains
- I always have circulation, regardless of how "full" the skimmer gets (I have them both cut in full at the pump)
- Draining of the pool (excess water from rain, or draining to winterize) is easy


I will say, the skimmer works best without the main drains being cut in, but that is also dependent on a single return being used (seemed to force the largest amount of floating garbage to the outside quicker).

But, with both returns, the main drain and the skimmer all operating full, the pool had the best circulation, the surface always stayed clear, the garbage collected near the main drains as much as possible (which means vacuuming was kept to minimum, since all you do it shut off the skimmer and the main drains sucked in as much as possible) and in general the pool was as low-maintenance as possible.

Dennis, Can I post and this may wind you up a bit but I don't mean to, just trying to go nearer to what really takes place?
Increased circulation of mainly clean water from midway down the pool?
Collection of debris at the bottom near the drains, if the skimming action was working well there wouldn't be debris on the bottom? Dirt enters from the surface first? Near, near the main drains, not into the main drains so not clearing the debris unless you push it in, so misses the dirt and just circulates cleaner water from above the dirt layer.
I always have circulation regardless of how full the skimmer gets, A second skimmer? for the reasons stated above?
Draining the pool, well yes that's why they were fitted but a submersible pump or opening a return?

I can see the heating point though.
Please don't take this the wrong way, I am just discussing.

[DennisP]

Oh, no big deal on the discussion... I take no offense...

Well, without going into too much detail, I think you are oversimplifying the way water currents work and the way any body of water reacts to not only currents, but how debris within those currents get filtered out...

Honestly, I think two skimmers AND main drains would be beneficial in a pool where you have debris making it's way in (such as trees/excessive winds/etc)... Now is a second skimmer going to make a 100% difference, no. Will it make a 30-50% difference, for a pool with lots of floating debris, sure.

Now, for me, the big issue for main drains is not for just the ability to drain the pool. It is for all the reasons I stated above. My pool stays cleaner, there is always good flow regardless of how full the skimmer gets, and I have great equalization of temp throughout the depth because of the constant pull of water from all areas in regards to heating.

In regards to debris, only some debris will float. Only what floats will get sucked into the skimmer. Anything else that falls to the bottom will stay there, unless it gets sucked into a main drain. Now, does that mean that all debris that falls to the bottom goes into the main drains, no. But, from experience, a substantial portion does make it's way either into the main drains, or close enough that while vacuuming it is easy enough to push whatever will go into the main drains and whatever is left actually gets sucked up by the vacuum. ie, the pool is much cleaner with less work with a main drain compared to not having one. I must also point out the folly of assuming that you have full circulation if you only have a skimmer and the skimmer basket gets full. That is far from my experience with large leaves that get sucked up in my installation, as it is obvious that when the skimmer gets full the majority of water gets pulled from the main drains by way of the amount of floating debris that still exists on the surface, yet when I cut to only pull from the skimmer in such cases I get a huge reduction of output from the returns...

as far as draining the pool, there is a huge difference from using a main drain with 2" piping and a submersible pump. The main drain allows for full pipe volume in draining, with the pump only allowing for the max hose size you can connect in draining. Apples and oranges in comparison, since there isn't any. It took me all of 30 minutes to drain the pool enough with the pump running and the main drains cut in exclusively. With a submersible pump I would have been lucky to do the same in 12 hours. There is a massive difference in volume between the two. Opening a return is only valid if you wish to flood the immediate area with chlorinated water, and even then you wouldn't have the speed of using main drains with the pump running.

I do agree that a lot of dirt settles to the bottom and stays there, regardless of how many returns or skimmers/drains, so you will always have the need to vacuum the pool at times (or use an automated pool cleaner), but I can attest to the fact that the pool stays way cleaner with main drains running along with the skimmer overall, so cleaning via vacuum/automated pool cleaner is reduced in all cases, especially in mine.

[J_Palmer_Cass]

Thanks for the reply Dennis.

And, from your perspective, being a pool installation professional, I can understand your motivations to keep the "common owners" from going with a main drain.

I am far from a "common owner", and I have noticed that a large number of those on the web posting about pools seem to be those are are far removed from being engineering types, handyman types and/or those with mechanical proficiency.

So, as you said, for the majority of people, no main drain is common sense. But, for those of us "with a clue and ability" a main drain is essential.

Without a main drain winterizing is a PITA. Without a main drain you can't circulate water while heating a pool and melting the ice the formed over winter for an early spring opening (which I did this year, which required using only the main drain to pull water out, circulate it through the heater and then send heated water back to the pool while also allowing me to fill the pool with my dedicated fill bib and line setup)... My kids were swimming the first week of March when we hit 70 degrees for a day or two. Without a main drain that would have been impossible as I would have had to fill the pool first to use the skimmer, then I would have had the issue of ice shards plugging the skimmer (which would have prevented flow through the system to use the heater)...

I just want to be sure that those that are true DIY types that are extremely detail oriented seriously consider a main drain setup for it's many advantages. Those hiring others to do everything need not consider it.

I must say that I have never attempted to heat a pool while there was still ice on the surface. Kind of a luxury heating an outdoor pool while it is still "winter". Kind of hard to remove the pool cover when there is ice and snow on it!

That being said, I would never put a main drain in the bottom of an above pool liner. Too much risk of a leak for my taste, with very little benefit. I also prefer an easy way to winterize the pool. Having water lines below grade are not for me. The only time I have ever drained the pool was when the liner was replaced, so I don't need to worry about drain time.

I have a Fanta Sea 16' x 32' x 4' flat bottom pool that is now on its third vinyl liner. The pool has one skimmer, one pump outlet, and one lower drain/pump feed on the sidewall about 5" from the bottom of the pool. Circulation is fine. However, over time debris does settle in the center of the pool. That's pretty much to be expected due the circulation pattern. Then again, I only vacuum the pool once a month.

[mas985]

Many PBs are building pools now without main drains but not because they don't have a clue or because they are trying to save costs but because studies have shown that they really don't contribute much to the sanitation and cleanliness of a pool. Here is one such study done by the APSP: http://apsp.org/portals/0/PDFs/Case%...n%20Drains.pdf

The video at the end shows how ineffective a main drain really is even at very high flow rates. I have confirmed this myself with my own pool since I have a MD and have operated with it on and with it off and I saw absolutely no difference in water quality or bottom cleanliness. I once dumped a bucket of small debris around the MD and even with the pump running over 8 hours with ONLY the MD running, only the first couple of inches around the MD were free of debris. Because of the VGBA, MDs are now designed to have very low water velocity to reduce the risk of entrapment which makes these MDs even worse at drawing in debris. While you may have seen debris setting around the MDs, that could be due to the slope in the floor rather than the MD itself.

But there is another significant reason not use MDs. Skimmers require a certain flow rate in order to effectively draw in debris. Some manufactures recommend at least 15 GPM. With the addition of an MD, it steals water from the skimmer and there may not be enough suction on low speed of a two speed pump so running on high speed may be necessary which is about 4x the energy use. Same is true with a VS pump. More suction ports require higher RPM settings and higher energy costs.

Sorry but I really think you are fooling yourself into thinking that the MD is actually doing anything at all. The evidence simply doesn't support it.