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

[mas985]

To argue that is just showing how ignorant you are being.

Really? You have to hurl personal insults to prove your point? I guess you have to attack the messenger because you can't argue the message.

[DennisP]

Not at all... It is a very simple principle that you have been arguing against aimlessly for this entire thread. Simple, cool water sits at the bottom. Warm water at top. Cool water gets sucked in, warm water gets injected. Complete turnover with the shortest amount of time. You will NOT have that without pulling water from the furthest, lowest point of the pool while returning water at a higher further point away. C'mon, how hard is that to understand??!?!?!?

Basically you are trying to say the sky is not blue because you are color blind and a study by color blind people is stating that the sky is mauve... I am not color blind, I know the sky is blue and I know what happens in my own pool. I pay my heating bill. I have a HUGE financial motivation to make sure I get the quickest result in the shortest time.

[mas985]

Not at all... It is a very simple principle that you have been arguing against aimlessly for this entire thread. Simple, cool water sits at the bottom. Warm water at top. Cool water gets sucked in, warm water gets injected. Complete turnover with the shortest amount of time. You will NOT have that without pulling water from the furthest, lowest point of the pool while returning water at a higher further point away. C'mon, how hard is that to understand??!?!?!?

I understand that very well and was not arguing that point at all. But the effect only occurs as long as there is a temperature difference between the surface and the bottom. My main point is that after the pump turns on, any temperature difference disappears very quickly (< 30 min) because the returns mix the water pretty effectively. So I fail to see how the heating efficiency is going to be affected that much by a main drain especially when the pool is only 4' deep. I maintain that it will still take about the same amount of time to heat a pool 1 degree with or without a main drain (~40 min) and if you measure the temperature difference of the top vs bottom of the pool, it will be about the same after about 30 min.

Remember too that this site and other pool sites recommend a 30 min run time to fully mix added chemicals throughout the pool so there is precedence to the fact that mixture of chemicals, and by proxy heat, throughout the water usually occurs within about 30 min.

[DennisP]

And I thoroughly disagree on your "conclusions"... Even with just over 4ft of water I can tell a difference in temp between the upper levels and the bottom without the main drains. With them on it is drastically different.

I would argue your assumption that since chemicals mix that temperature variances are also nil. That is far from the case.

Again, believe what you want. I have direct observation and quantifiable results to backup what I have posted. And unless you have the exact same pool setup, in the exact same environment, you have no point of reference other than flawed studies to fall back upon. I am an engineer, but far from blinded enough to think that those are the only answers and fully realize there are environmental factors that change everything compared to a set of "fixed examples". Your diatribe on pump dynamics show that you understand those aspects of engineering, so why be so obtuse on this???

[mas985]

Even with just over 4ft of water I can tell a difference in temp between the upper levels and the bottom without the main drains. With them on it is drastically different.

Within the first few minutes of the pump turning on, I would agree but I think you would have to agree that at some point even without a MD, the water temps would eventually equalize. It is illogical to think that the water temps would remain different at the top and bottom of the pool forever while the pump is running and constantly mixing the water. Even with a single return pointed horizontally, you would see with a dye test, return water mixing with the pool water at all levels of the pool. I really don't think it would take long at all for the temperatures to equalize.


But let me be clear, I am not disputing that MDs help to equalize the temperature difference. What I am saying is that there are other ways to accomplish same thing and they are equally as effective. As I mentioned before, I have one of my returns pointed down to my deep end and the deep end temperature at 9' equalizes very quickly, within minutes. So instead of a MD, you could have added a lower return and had the same results.

I would argue your assumption that since chemicals mix that temperature variances are also nil. That is far from the case.

Why would it not be the case? Both heat and chemicals move along with the water currents as they are both part of the water. Seems logical to me.

you have no point of reference other than flawed studies to fall back upon.

Actually I do, my own measurements and observations as well as a few posts from other POs that have pools without MDs and have no such problem with temperature difference. But why do you think these studies are flawed? They were performed by well respected universities and organizations. If you have any other contradictory scientific evidence then please share it. My point with the studies is that somebody actually went to the trouble of running experiments and simulations and documenting the results. This is what engineers and scientist do to confirm hypotheses.


I understand your reluctance to accept this evidence because you went to the expense and trouble of installing the MD and you really want it to have a benefit that you could not possibly have achieved in any other way but to me, the evidence is indisputable.

[Anonymous [GDPR] European in the UK]

And I thoroughly disagree on your "conclusions"... Even with just over 4ft of water I can tell a difference in temp between the upper levels and the bottom without the main drains. With them on it is drastically different.

I would argue your assumption that since chemicals mix that temperature variances are also nil. That is far from the case.

Again, believe what you want. I have direct observation and quantifiable results to backup what I have posted. And unless you have the exact same pool setup, in the exact same environment, you have no point of reference other than flawed studies to fall back upon. I am an engineer, but far from blinded enough to think that those are the only answers and fully realize there are environmental factors that change everything compared to a set of "fixed examples". Your diatribe on pump dynamics show that you understand those aspects of engineering, so why be so obtuse on this???

Oh, I don't follow your ideas Dennis and your Facts are not really facts they are as you see it but not facts.
Of course you get better flow with you M/D's as you don't have more than the 1 skimmer? how can you possible get the same flow with 1 skimmer compared to when the M/D's are involved?
As to the M/D's getting your pool up to temperature, it depends where your thermometer is. I have the pleasure of playing with pools set up like yours and also ones I have put a 3 port valve on so I can switch the M/D's from inlet to outlet.
Now you believe taking cold water from the bottom and feeding it into the top via returns is quickest. I don't, the water at the surface is warmer (fact) take the water from there and it takes less energy and therefore less time to heat that up than the colder water from the bottom that's a fact to. feed that into the bottom of the pool via the M/D's and the lower part of the pool gets warmer quicker as you said it causes things to mix quicker, yes it does whether it's used as an inlet or an outlet is mixes more that's a fact, you've agreed, I have tested it, it follows physics and you can't mess with physics.

The daft thing you said back a few posts about taking out your other return and wishing you hadn't put it? Go for it Mr engineer! then you'll loose performance as the friction and restriction you'll place on the system will create a great big headloss. You cannot compress a liquid so you can only get into the pump via skimmer and M/D's what the return line will allow to flow, the headloss and friction is just wasted energy.

I am not bemoaning M/D's, I was amazed that pools without them worked at first, the guy who taught me thought as you did. My pool doesn't have a M/D but I don't have a robot cleaner either as I don't need it a net and a pool Blaster Max is all I have and the Max is only for shear quickness as there is bound to be one leaf that misses the skimmers but my debris is taken out before it sinks in most cases but you are right I have to empty my skimmers more often.

Dennis where is the floor in the studies? they use the same software that keeps planes in the air and the maths behind it is very very accurate, the same is used in films to generate waves and fluid movements?
You need a study to prove it's floored, is there one?

[J_Palmer_Cass]

Regardless of the so called benefits of having a pair of master drains on the pool floor, they would be of little use to me. I do heat the pool with solar deck panels.

First, it is hard enough to properly place a pool liner exactly where it belongs when you only have to locate sidewall drains, skimmers and the return. Floor drains just makes the liner installation difficult.

Second, I don't want to have to deal with winterizing the piping that feeds the floor drains. Not quite sure how I could winterize the master drain plumbing with my pool setup either.

My pool liner fits like a glove, and I doubt that it would fit that well if I had used floor mounted master drains.

[mas985]

Yes the bullet does but it also has a way higher velocity, it's path decays so quickly as the water put's up an opposing force (Newton's 3rd law of motion).

But you are neglecting the movement of the water itself. When the pump first turns on, there is a lot of resistance but as time goes on and the pool currents are setup, the resistive force is reduced and the directional flow moves further and further away from the return reaching farther areas of the pool.

Also, I didn't mean to imply that the currents are only in one straight direction. I was mainly referring the fact that water does not drop like the bullet does. I understand that the water travels more or less in a cone and the cone angle is dependent upon the orifice size and shape.

except the single lines for the returns is way too much

You mentioned that you try to keep the port size the same between the suction and return sides but the above quote would indicate that you do not bring those same ports sizes (i.e diameter) all the way to the pump for at least the return side. If that is the case, the return side would definitely have more head loss due to less parallel pipe paths than the suction side. So I have to ask, isn't that defeating the purpose of the whole "port size" objective? Pipe, fittings and the exit orifice all add head loss to varying degrees so I don't see any benefit having the port sizes equal other than they have slightly less head loss than a smaller orifice eyeball. Is that the main objective?

Also, I am curious about your pump. Can you give more details about it (make/model)?