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I've seen in piping and ventilation systems, when they branch off, the continuation of the main trunk gets smaller. Presumably this keeps the pressure (sorta) constant along the whole length of the main trunk.

So I wanna do this with a swimming pool pump return. My current outlets are about 9' off the pool bottom (very old in-ground). This causes a dead spot in the middle of the pool where cr*p collects and it's also the hardest to reach with the vacuum.

My thought is a single pipe running vertically down the sidewall with a number of holes drilled into it - try to get the water flowing "differently" than it does now. Ideally I eliminate this dead spot.

I'm not interested in lowering the diameter of the pipe so much as much changing the size of the holes (presumably smaller holes at the top where the pressure is higher).

Anyhow, there's gotta be an equation or method for determining this, but I'm only a lowly electronics engineer.. I never took any fluid dynamics classes! So I don't know what this principal is called so I can't even Google it effectively. Anything is better than me just guessing at it, so what'cha got??

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  • $\begingroup$ Before jumping down the rabbit hole of flow calculations, try just attaching a hose to one of your outlets and aiming it at the crap zone. Maybe put a weight on the end of the hose to keep it in place. Then use trial and error to figure out a good hose placement. $\endgroup$
    – Carlton
    Commented Aug 26, 2020 at 20:42
  • $\begingroup$ Fluid Mechanics For Gravity – Flow Water Systems and Pumps walks you through the math. Contunuity and Bernoulli. $\endgroup$
    – StainlessSteelRat
    Commented Aug 29, 2020 at 18:10

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This is a hard problem. Flow through an orifice is already hard to predict, and now you're changing the pressure of the exist due to depth of water.

Without going through a bunch of calcs, I suspect that unless you have a crazy big pump going through this pipe you won't get much from it with holes in it. I think better would be a single nozzle or two blowing at your zone of cr@p. If you want more outlets, nozzles with valves you can adjust (or just adjustable nozzles) let you do it yourself based on being there and getting it exactly how you want it. HVAC systems are designed like you say, but usually also have dampers because it's never quite right.

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  • $\begingroup$ Thanks for the reply! Yes, my pump is 'crazy powerful' - I over-bought it when I replaced it last year. If/when it burns out, I'll drop down a step in HP. The idea I have isn't so much to blow the stuff on the floor, rather to ensure the entire pool water circulates. As it is now, seems only the top few feet have any movement. The deep zone is basically stagnant. The holes I envision are maybe 3/8" - 1/2"?? But a bunch of them. So I guess what you're saying is, I SHOULD guess at it, make small holes, and see how it works. I can always drill them bigger later. $\endgroup$
    – Kyle B
    Commented Aug 26, 2020 at 14:02
  • $\begingroup$ I mean... it's a swimming pool, not a cooling system on a jet engine ;) It doesn't have to be optimally setup. It just has to be better than what it is! $\endgroup$
    – Kyle B
    Commented Aug 26, 2020 at 14:05
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I agree with @Tiger Guy's answer.

Pool filters have a wide range of working pressure starting from 50psi or more when clean to near zero when dirty. That makes the flow of your orifices very unpredictable.

Also to keep the stagnate zones in circulation you need minimal flow out of a miniature nuzzle.

There are pool robots in the $300.00 range that connect to your skimmer if your pool is very old and does not have a vacuum outlet. They do a great job crawling to every corner and trapping everything, dirt, algae, or big leaves.

If you are curious about the hydraulics of orifices just drill some holes along a vertical line on a bucket and fill it with water, the lower the hole the wider they spray.

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  • $\begingroup$ Thanks for the reply! If a robot were that cheap I'd consider it. Ingrounds require the motorized versions though cuz the lower cost units only work on flat floors. Anyhow I dont want ANOTHER piece of gear to maintain... $\endgroup$
    – Kyle B
    Commented Aug 27, 2020 at 2:10

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