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Thread: Pressure test, and results

  1. Back To Top    #1

    In the Industry

    Join Date
    Jun 2010
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    74

    Pressure test, and results

    I did a pressure test on a pool recently to try and narrow down the source of some vacuum problems. The issue is that after about 5 minutes, the pump starts pulling a ton of air out of absolutely nowhere. From then on, lots of air moves through with the water, making vacuuming very difficult as the pump goes through a repeating prime-run-cavitate-try-again cycle. This ONLY happens when vacuuming. A new hose did not help. This problem has gotten a little worse every year.

    First, let's verify that I did the test right. This particular 25-year-old pool has dual main drains and two skimmers. The two skimmers come into the pump house in a single line; they are not separate. I plugged one skimmer with a threaded plug and closed the skimmer isolation valve near the pump. In the other skimmer, I set up an assembly consisting of a pipe with a threaded adapter on one end (screwed into the skimmer), and a pressure gauge, a ball valve, and a hose bib at the other end.

    I tested the incoming water at 35 PSI. After hooking up the hose and turning it on, I opened the ball valve. I expected to see the pressure climb to the 30-35 PSI range, same as the hose pressure, at which point I would close the ball valve and see if the pressure dropped over the course of 10 minutes or so. What I got instead was that the water pressure never climbed over 4 PSI, no matter how long I left it on. Perplexed, I traded the plug and moved to the other skimmer (closer to the pump house). At this skimmer I got 7 PSI, and again no higher. Just to be sure there wasn't a hidden cross connection to the main drain, I poured a bunch of dye into one skimmer and forced water into it. The dye came out of the other skimmer, but not from the main drain or any other location.

    I believe this suggests that I have a large break somewhere in the skimmer line. My theory is that the ground around the break is flooded (from leaking), and after years probably has a hollow around it. I think that when I am vacuuming, three or four times the normal suction is put through one skimmer, pulling water back in the break - and after roughly 5 minutes of this, the hollow is evacuated and air starts getting pulled in.

    Does this sound right, or am I way off base or missing something? (I will be doing a pressure test on another site on Monday so it would be good to know I was doing it right...)
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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    Apr 2013
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    Sacramento, CA
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    Re: Pressure test, and results

    Your presure test sounds correct. And I agree with your conclusion. However, why is this only happening when vacuuming? Shouldn't it be sucking air at other times also?
    22k gallon IG pebblefina, Jandy 1.5 HP VS, Jandy CV Cartridge filter, Fafco solar panels, Polaris 360 supply side cleaner, waterfall

  3. Back To Top    #3

    In the Industry

    Join Date
    Jun 2010
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    74

    Re: Pressure test, and results

    My best guess is that at normal times, the suction through the skimmer line is not enough to actually cause suction through the break, so it allows a LEAK. This explains the water loss we get (about 2" a day in a 20x44' pool). Roughly 50% of the pump's suction goes through the main drain; of the remaining 50%, roughly half would go to each skimmer. So if the break is before the skimmers meet up, only 25% of the pump's suction is at the break. If it's after, it's still only 50% of the pump's suction. When vacuuming, we close the main drain isolation valve and plug the other skimmer, so 100% of the pump's suction is going through that one skimmer - which must be enough to reverse the flow through the break.
    * Responsible for the operation of 21 semi-private pools and spas at 11 locations, varying from 1,900L to 20,000L spas and from 13,000L to 200,000L pools.

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