Hi All! I hired a GC for Underslab plumbing and they tested the DWV at 5 psi. The pressure held for an hour then slowly dropped to 0 psi after 8 hrs. Is it normal to have 0 pressure after a period of time or could it be a possible leak? …I’m not sure about this. I read the AHJ requires DWV to hold 5 psi for 15 minutes. Thnx for any feedback, opinion!

IF the pressure held for over an hour, when only a shorter term is required, then it should have passed.

Thnx for the quick reply! And that’s what I’m reading though I’ve not ordered the inspection yet. But the plumber said they’ll look for a leak as if some pressure should remain. I’d like to know if a DWV pressure test can read 0 psi after time (contrary to water supply lines) and not necessarily be an issue. Of course it’s my decision what caused drop in pressure, just need some input. Thnx again!

you can always pump it up again and spray bubble water on the joints looking for bubbles.

The AHJ is looking for MINIMUM code.

What YOU want is good or best practice.

Of course there should be 'some' pressure left after 8 hours.

? Where did it go ? LEAKAGE

Thnx packy. I tried that, didn’t notice anything. But pressure was low (2 psi) and I can’t test the section of pipe on the ground. …I may pressurize at 5 psi and try again.

Great bernabeu! The info will help me make an informative decision. Btw Plumber will retest DWV system today which tells me 0 psi is problematic.

test it with a static 10 foot 'head' of water (approx 4.32 psi)

level/pressure should NOT drop at all

every once in a while, my friend from SC shows brilliance.
if it is not practical to stand up a 10 foot tall pipe, simply do a hydrostatic test.

What Is Hydrostatic Testing?
Fill the pipeline with a liquid, mostly water, unless its material is incompatible with water.
Apply pressure to the pipeline to bring it to its acceptable test pressure. ...
Hold the pressure for a required timeframe to examine the pipeline for possible leakages.

the 10' pipe IS the hydrostatic test

hydro = water / static = no motion



a 'cheat' would be to fill with water, pressurize with 5 psi air FROM THE VERY TOP depressurize after 1/2 hour and see if the water level dropped AT ALL

that would be called a hydro-pressure test

hydro-pressure test - Interesting!



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Thnx bernabeu and packy for the suggestions! Yes, the plumber has conducted both tests (hydrostatic and air) but same result - failed. Avoidable mistakes like end cap leak or plug blows off the exit pipe. And to move expeditiously isn’t their strong suit. This GC’s workforce is spread too thin imo. …a 7 day project is now a month!

Anyway they’ll TRY to finish repairs and re-test today, I’ll update you….



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The plumber arrived this morning and I thanked him! The system is pressurized at 6 psi (hydro-pressure test) and holding! I’ll watch it today and hope to call for tomorrow inspection.

it is the water LEVEL, not the AIR PRESSURE, which is important

the air PRESSURE will act somewhat like an expansion/compression tank and 'tend' to remain constant, especially if charged in the AM of a rapidly warming Arizona day

Open the topmost fitting, fill the system with water to the very top, add a nipple and valve, top 'er off with water, pressurize with a bicycle pump to about 4, close the valve, come back 'later' to see if the water LEVEL dropped.

I’m sold on hydro-pressure test, a good way to find leaks. The plumber pressurized the system and a couple hours later I hand checked each pipe joint and found two leaks (water on my fingers). …very cool!

since the probability of leaks (plural) is real, i would strongly suggest the plumber mixes a fluorescent dye into the water and then pressurizes the piping.
they will know what you are talking about.
the dye will make any leaks much easier to find.

[www.amazon.com]

funny story...
i knew of one inspector who would come out to the job, look at the gauge for five pounds and then ask to have something opened up so he could hear the air rushing out. yeah, some plumbers actually have a gauge that the hand is stuck on 5 PSI.

Thnx packy for the dye suggestion and link. …I did mention it to the plumber. Anyway I’m at a standstill waiting for repairs and running out of time and patience!



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Plumber is here! …let’s all pray and I feel lucky

Underslab DWV pressure test Passed!!
Thnx everyone for suggestions and encouragement. I’ll be back as I continue the build. Cheers



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