Closed loop or no closed loop on an irregular shape pool??????

neednewpoolSeptember 21, 2010

The work has started on my remodel which includes totally new plumbing. If I want him to do so, the contractor will install a 2" closed loop with 1.5" to each inlet. It was going to be 1 skimmer and 6 inlets but will be 2 skimmers and 4 inlets. My understanding from other posts here is the closed loop would result in equal pressure at all of the inlets. But he recommends an open loop with one 2" pipe for the west side and another 2" for the east side (the 2 longs sides of an irregular shape pool). He dos not think that an equal amount of pressure to each inlet is right for my pool because one inlet needs to push the water much further than the others. Each 2" pipe would have a manual valve to adjust how much of the water goes to each. Because of the location of the skimmers and the shape of the pool, the west pipe will have 3 inlets but the east pipe will only have 1 (the 1 skimmer is on the shallow end of the east side and the other is at the deep end of the east side). So almost all of the east side and most of the south side will not have any inlets. The 4 inlets are positioned to move the water counter clockwise to the skimmers.

The closed loop certainly made sense when the plan was 1 skimmer and inlets but this does make sense with 2 skimmers and 4 inlets. The pool is surrounded on 3 sides by many large trees. So I do get a LOT of leaves in the pool which is why he suggested the 2nd skimmer. FYI, he is not charging me extra to add the 2nd skimmer and delete 2 inlets. He will do either for the same price.

Please let me know what you would do. Thank you

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mas985

A closed loop "helps" to equalize pressure amongst the returns but it is not perfect either. However, you don't necessarily need a closed loop to equalize pressure as there are other ways to do that but requires a little knowledge of head loss and hydraulics. Simply using a large diameter header connecting the returns can help. Your PB may be right that he wants more flow out of one of the returns than the others. Really having exactly equal pressure is more important for spa jets then it is for pool returns.

It is hard to know for sure what his plan is without a drawing and knowing the size of the pool and the placement of the returns and skimmers. Perhaps the most important thing is the placement of the skimmers. You want one down wind because in reality, once the wind starts to blow, the returns really won't be able to fight against the wind anyway.

One option would be to run 4 x 1.5" pipes from the equipment to the pool all with ball valves. That way you can control the flow rate to each return for fine tuning. This would be equivalent to runing a single 2.5" line or two 2" lines. But if the one return really needs that much more flow rate than the others, then you might want to use 2" line for that one but I don't really see why it would. Again a drawing might help.

    Bookmark   September 22, 2010 at 11:21AM
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rice_rocket

The other thing is that if you're in the northern hemisphere, water tends to spin clockwise going down a drain. When you "wire" a pool to flow counter-clockwise in this situation, aren't you actually going "uphill" so to speak? Just sayin'...

    Bookmark   September 22, 2010 at 9:07PM
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lbridges

The Coriolis force has an impact to large things such as a tropical storm or the muddy flow from the Mississippi River into the Gulf of Mexico, but it isn't large enough to cause water to spin in any one direction down a drain. It also varies by latitude - the force increasing proportionally to the latitude increasing (slower Earth rotation).

While I will admit I haven't calculated the strength, I'm pretty sure it doesn't apply even to a large pool.

As a physicist, just sayin' :)

    Bookmark   September 22, 2010 at 10:25PM
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fighting_irish

Accually I have found that the Coriolis force does effect a pool as a whole.

Many years ago I had a pool that was having circulation issues and could not figure out the problem. Again this was very early in my career as a builder. But after reading up on the Coriolis force. I decided the place all my returns in a counter clockwise direction to see what would happen. Guess what not more issue. If you take the Coriolis force and you add the assist of a circulation pump. I do think that there is an effect on a pool.

JMO,

David

    Bookmark   September 23, 2010 at 8:51AM
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just-a-pb

We are off issue, but a pool is too small to have any Coriolis force effect. Even the oceans are more effected by the winds (which are effected by Coriolis) then the movement itself.
Myths are so fun.

Irish you may have been fighting a natural wind pattern and when you swapped direction it worked better.

    Bookmark   September 23, 2010 at 9:54AM
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fighting_irish

I meant to put this may have been coincidence. And yes I took the closed or open loop question off topic. The comment just looked to intriguing to pass up. Anyway please ignore me and carry on.

David

    Bookmark   September 23, 2010 at 10:03AM
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rice_rocket

Sorry about that--I was just curious.

    Bookmark   September 23, 2010 at 1:34PM
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ncrealestateguy

Isn't the Coriolis Effect the reason why our toilets, when flushed, go clockwise? Don't toilets in the Southern hemisphere spin counter clockwise? Same for tornadoes, which in the scope of things are very small, intense storms.

    Bookmark   September 23, 2010 at 2:19PM
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rice_rocket

I think the toilets design has more to do with the flush direction than Coriolis.

    Bookmark   September 23, 2010 at 4:27PM
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mas985

The whole toliet and bathtub thing is a myth. The forces in that size body of water is just too small. Wiki has a very good description of the Coriolis effect as well as the bathtub myth.

Here is a link that might be useful: Coriolis Effect

    Bookmark   September 23, 2010 at 5:25PM
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trhought

neednewpool...bet you didn't think this post would go the direction it did and bring out the geek in all of us.

The closed loop proposal with 2 skimmers and adjustable flow sounds OK. This will allow flow to be changed depending on skimming needs and 2 skimmers is better than one. Agree with mas985...a drawing would help showing skimmers and return locations relative to shape of your pool.

Regarding the coreolis effect...this acceleration is directly proportional to the normal acceleration of the body in question. In the case of a swimming pool...the swirling effect is negligible unless your main drain was say 3 feet in diameter and you were moving over 100,000 gallons per minute through the main drain. This would create a high normal acceleration (movement of water down the drain) that would impose a noticeable coreolis acceleration (swirling) in the pool. The depth of the pool above the main drain would also be a factor for this academic exercise....the deeper the pool the less swirling at the surface.

For us mortals who are only moving 30-100 gpm in our pools, we don't have to worry about the coreolis effect on skimming action...Thank goodness! We just have to worry about wind patterns, and pushing debris towards the skimmers.

Hope this helps.

    Bookmark   September 23, 2010 at 8:49PM
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