I need to make a water trap

cmc0619

Gold Supporter
May 2, 2018
132
Cherry Hill, NJ
Hi TFP
I'm adding sensors to my DIY controller and I need some hydrodynamics advice. The sensors I'm using aren't supposed to get dry so I need to keep them in the pool water at all times. I was thinking of creating a p-trap to my pad plumbing like they do on sinks to keep water there.

Will this work? I'm worried about suction pulling water out of this low spot when the pump shuts off. Would there be a benefit to adding a check valve before or after the manifold or am I worried about nothing? I plan to install this unit in between filter out and heater in and it's low spot will be approx 6-12 inches above the pump output.

I'm less worried about added head pressure as I'm redoing my piping and removing lots of bends and replacing the existing 90s with sweep 90s so whatever I lose with this p-trap setup I'm hopefully net equal with the changes I've made in other spots.

Any thoughts, comments or things to consider are welcome before I start gluing this all together.
Thanks!
Cliff

IMG_6843.jpg
 

RMcGirr83

Gold Supporter
Nov 19, 2018
877
Tuscola, TX
I believe, unless you have an air leak, you'll always have water in the piping. I don't see anything wrong with putting in a p-trap but what would happen if the plumbing lost pressure and the water behind the trap turned into air? When you start the pump, the sensors wouldn't be sitting in water for a bit until everything got pressurized.
 

Brett S

Well-known member
Mar 15, 2019
626
Orlando
I’m not sure that would work. A P-Trap in a normal drain is very different because the drain is open to the air with vents and has a pretty slow flow because it’s just using gravity to drain the water.

Pool plumbing is a closed system, and like Rich said above the plumbing will normally be full of water, even when the pumps are off.

If air is introduced into the system and the water drains from the pipe I believe it will siphon out and even drain the water from your little trap.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,584
Pleasanton, CA
Do you have solar? If not, then water should remain in the plumbing. But even if the pipe emptied, the sensors should still remain damp just not submerged so they should not be completely dry.

BTW, are those Sch40 90's? Do not use regular DWV pipe. It is not as strong as Sch40.
 

Newdude

Well-known member
Jun 16, 2019
3,660
NY
If air is introduced into the system and the water drains from the pipe I believe it will siphon out and even drain the water from your little trap.
It will drain but when it gets to the last bit it will start to drain the bottom of the trap, suck air and the water will fall back into the trap filling it halfway or more. If there is enough volume in the vertical drop it will fill the whole bottom piece when it does.
 
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cmc0619

Gold Supporter
May 2, 2018
132
Cherry Hill, NJ
Ok! So it sounds like this might work! I didn't think about the closed system keeping water in the pipes at all times. The sensors can be damp for an amount of time, I think they're just not supposed to dry out. Also, while writing this, I just realized I have a check valve between the most likely source of air (opening the pump basket lid) in the form of a flowmeter (idk why, it was there when I bought the house/pool) and this setup which probably makes this question moot.

These are Sch40 Pool Sweeps. 409-020SW. I only use DWV as on-ramps for the kids hot wheel tunnels we build out of my surplus PVC. :D

Thanks for the feedback!

EDIT:I just came up with a backup plan too. Behold this beautiful picture... :)
Reallybadpictureofptrap.png
 
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RDspaguy

In The Industry
Mar 21, 2020
752
Cabool, Mo
Use standard pressure fittings, sweeps are not saving you enough head to matter. And be prepared for a bit more trouble priming because you are making an air trap as well as a water trap.
 
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