Anyone heard of, or had experience with flow-reversal?

[DennisP]

Here is my equipment setup:

- Pentair Dynamo 1.5hp 2-speed pump
- Sta-Rite System3 cartridge filter (300sq/ft)
- Jandy Lite2 250k BTU NG pool hater (millivolt unit)
- Jandy check and 3-way valves
- all 2" plumbing from the pool to the equipment pad and at the pad
- three 2" lines installed and one 3/4" line installed for configurability

I plan on adding a 15gallon chlorine tank with Stenner pump in the future along with possibly a booster pump and pressure cleaner or a robotic or vacuum cleaner. I am installing dual main drains to comply with code and to remove any concern about "entrapment".

I talked to a few people and if you have good circulation in the pool with plenty of turbulence at the bottom the main drains are supposed to do quite a good job of minimizing vacuuming. I figure for the minimal expense (I am doing the complete install myself) it would probably be worthwhile.

[DennisP]

Pics of the equipment pad can be found in this thread: http://www.poolforum.com/pf2/showthr...065#post126065

[nefretrameses]

I heard of this with respect to solar heating panels. I don't recall where. I think their premise was the same as yours - warm water introduced at the bottom will push colder water up where it will be picked up for solar heating or something like that. But I think solar introduces a temperature delta irrespective of the input water temperature (within a relevant range). It sounds like there's not a significant difference anyway. I'd trust Mark's analysis and opinion.

[mas985]

I talked to a few people and if you have good circulation in the pool with plenty of turbulence at the bottom the main drains are supposed to do quite a good job of minimizing vacuuming.

Sorry but I think these "people" are just misguided and do not understand hydraulics very well. I have main drains and I can tell you they don't do anything. This is especially true of dual main drains with safety covers. The reduction in entrapment also reduces the force of the water in any one direction (done on purpose) so they do move anything very well. That is why they lower entrapment.

Perhaps you should read this article and watch the video if you still do not believe me:

http://www.poolinspections.com/manua...out-drains.pdf

https://www.youtube.com/watch?v=0IOUGhuKkSM

[DennisP]

I had a whole reply typed and lost it due to a browser error...

Long story short, I cannot see how having extra suction inlets are ever a negative. If a single skimmer is sufficient, then adding a few extra drains cannot hurt. I have 5 kids and have zero concern of entrapment due to dual drains tee'd together, and a 30% skimmer limit at least fixed in. Even with a 2hp pump on high, there would not be enough suction to cause anyone to be stuck to a drain. I also am a maintenance freak, so if a drain cap is broken or something I guarantee no-one will use the pool until I replace it.

I figure on leaving the pump on low almost 24/7... At that I am concerned about proper mixing, thus I figure a single skimmer, two returns across from each other and dual drains about 6 feet apart should give me the best possibility for proper and complete turnover throughout the pool all the time.

I read the entire article and watched the video, and I have little issue with any of that... But, from a "what is ideal" situation where entrapment isn't a concern, I don't see an issue.

[JimK]

Interesting stuff.

When I was shopping for an inground pool back in 2003 I got quotes from 3 different pool companies. Two offered designs that included a main drain and one offered a design that had a return at the bottom of the deep end rather than a main drain.

I'd never heard of a pool without a main drain so I thought the company that didn't include one was cutting corners to increase profit (their pool was a little more expensive than the others). So we ended up with a design that included a main drain.

Based on the links provided it seems the company who didn't install main drains was on to something.

[JimK]

I had a whole reply typed and lost it due to a browser error...

Long story short, I cannot see how having extra suction inlets are ever a negative. If a single skimmer is sufficient, then adding a few extra drains cannot hurt. I have 5 kids and have zero concern of entrapment due to dual drains tee'd together, and a 30% skimmer limit at least fixed in. Even with a 2hp pump on high, there would not be enough suction to cause anyone to be stuck to a drain. I also am a maintenance freak, so if a drain cap is broken or something I guarantee no-one will use the pool until I replace it.

I figure on leaving the pump on low almost 24/7... At that I am concerned about proper mixing, thus I figure a single skimmer, two returns across from each other and dual drains about 6 feet apart should give me the best possibility for proper and complete turnover throughout the pool all the time.

I read the entire article and watched the video, and I have little issue with any of that... But, from a "what is ideal" situation where entrapment isn't a concern, I don't see an issue.

I'm also not concerned about entrapment in my pool (no kids btw). The main drain shares a pipe with two skimmers and there's no valve to shut off the skimmers (there is a valve to shut off the main drain). That combined with the main drain cover (checked on a regular bases to ensure its secure) there's simply not enough suction to entrap someone.

[mas985]

I have 5 kids and have zero concern of entrapment due to dual drains tee'd together, and a 30% skimmer limit at least fixed in.

Dual drains only eliminate one type of entrapment due to strong suction. However, they do not eliminate the chance of long hair getting stuck in the main drain. Nothing can prevent that (except short hair) so don't get a false sense of security.

As to other problems, main drains are the hardest items to fix but on a AG pool, they are a little easier to fix although you will still need to drain the pool so that is not a huge issue. But knowing what I do now, I would never put a MD in residential IG pool again let alone an AG pool which makes even less sense.

I figure on leaving the pump on low almost 24/7

That really isn't required either. There is an article in my signature on run time that you should read.

[DennisP]

mas985, so, your whole issue on main drains have everything to do with entrapment, and nothing to do with circulating water?

I have seen almost a "fanatical" take on stuff, and for being a hydraulics guy, I can't see why you are so against them. If it is fully because of the entrapment issue, fine. But, I am almost getting a feel it is like the "right to life" issue... Either you are pro-choice or pro-life and there is little middle-ground. You can definitely tell when reading certain technical articles on subjects like the main drain issue that there is a hard "slant" towards "NO MAIN DRAIN!" in some of them. But, just like people against high-hp cars because of the high chance of killing yourself/others with it, or even those that are "green" about energy efficiency vs those of us with gas-guzzlers. (I have a 1000+ HP car along with a 750hp car and a large conversion van, so I am far from the "tree-hugger" type, yet I am far from wasteful in regards to saving energy where it makes sense, but with 8 people in my household, we are major consumers of energy, food, gas, etc, etc) I just want the best available options for the best outcome. I hate being told that just because someone got hurt with something that I shouldn't do it, since in a lot of cases people get hurt due to ignorance, stupidity, lack of parental responsibility, etc, etc... All things that are avoidable if people use some reasonable thought processes.

In regards to having the pump on low 24/7, I am referring to the fact that I figure we will have high bather loads in the pool during the summer, thus with it running on low longer it would be better overall. But, that is just an initial thought and I will modify the low/high speed schedules as needed with a outlook towards shutting it off for as long as possible when it makes sense.

[mas985]

mas985, so, your whole issue on main drains have everything to do with entrapment, and nothing to do with circulating water?

Not quite. I just think there needs to be a clear benefit before making a modification. MDs don't seem to add any circulation benefit (see below) and they will reduce the flow rate to the skimmer (split flow). The entrapment issue just adds to the argument against them. Let me simplify.

PROS - NONE

CONS - Entrapment, leaks PLUS reduced skimmer action (flow rate is split)

If you were to put two identical pools side by side, one with a MD and one without, you would see absolutely no difference in water quality although because of the skimmer issue, the pool without the MD would have a cleaner surface than the pool with a MD. So what is the point? Keep it simple.

Maybe you missed this in the Main Drain article:

Myth
A main drain is essential in a pool to maintain healthy water.
Science does not support this conclusion. In fact, science concludes just the opposite. In a 2006
issue of Fluent News, the leading manufacturer of computational fluid dynamics software, an
article ran that compared pools with and without drains. The conclusion: there were no
significant differences between the circulations of the two pools. In fact, the skimmer-only pool
was slightly better.iv What is even more disturbing is that on page 50 of this same 2006 issue, the
software was used to model a revolutionary new swim skin technology that was sure to dominate
the upcoming 2008 Olympic Games. Pictured in that review: Michael Phelps, Olympic swimming gold medalist. The swim-speed technology was embraced, but the swim-safety
technology was essentially overlooked by the mainstream media