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Old 07-01-2012, 03:41 PM   #1
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Gas Pressure Testing With Manometer


I've heard some pros do gas line pressure testing with a manometer at low pressure as opposed to a #10 pound test using #15 gauge. Given how sensitive manometers are to local conditions, what pressure and time frame to pros use when doing a low pressure manometer test?

Background regarding this question, I recently had a plumber friend help me redo my gas lines to fix a few problems (undersized, galvanized not allowed by local code, electrical conduit couplings used ). I passed my inspection with the pipes holding #12 for multiple days.

I also picked up a used gas grill that came with a quick disconnect and hose. While they looked to be in good shape, I decided it'd be best to test them as well since they're no gas in the pipes yet. Since the quick disconnect has a max working pressure of only 1/2 psi, I built up a water manometer and started testing. I then spent a good chunk of last night worried that I had a decent gas leak until I realized that a 1 degree F change causes a drop of around 3/4" wc when at 1/2 psi. And when I was testing, there was a 1 to 1.5 F drop every 15 minutes according to a nearby weather station.

So do the fancy manometers automatically account for temperature & ambient pressure changes? Or do pros using manometers just plop a weather station down next to the pipe they're testing? I'm assuming that this is what lead to the #10 testing, since these sorts of changes would just be in the noise and not noticed.
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Old 07-01-2012, 03:57 PM   #2
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Gas Pressure Testing With Manometer


Quote:
Originally Posted by a_lost_shadow View Post
I've heard some pros do gas line pressure testing with a manometer at low pressure as opposed to a #10 pound test using #15 gauge. Given how sensitive manometers are to local conditions...
Your info says you're in Livermore, CA
Wild guess: are you some sort of engineer?
Quote:
I also picked up a used gas grill...
Natural gas? Propane?

Quote:
that came with a quick disconnect and hose. While they looked to be in good shape, I decided it'd be best to test them as well since they're no gas in the pipes yet.
No gas in what pipes? In any case...
if you have any reason to doubt the hose and QD just change them out.
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Old 07-01-2012, 04:19 PM   #3
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Gas Pressure Testing With Manometer


If your rough in piping passed the pressure test and your inspector is happy, final appliance and meter connections are tested with soap and water AND a dial test.
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Old 07-01-2012, 04:27 PM   #4
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Gas Pressure Testing With Manometer


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Originally Posted by TarheelTerp View Post
Your info says you're in Livermore, CA
Wild guess: are you some sort of engineer?
Almost...I got my masters in mechanical engineering, but enjoyed playing around with computers more so I jumped to a computer programming job instead of taking the tests required to be able to call myself an engineer. I also suffer from extreme curiosity, thus these types of questions.

It's a natural gas grill. And by no gas in the pipes, I meant that the new natural gas lines haven't been hooked up to the meter yet.

I was mostly worried about the possibility of a pinprick hole that I couldn't see in the hose. The hose looks great, but there's always that nagging voice of concern. Work has well beat into me the philosophy of test and test again if there's a chance of someone getting hurt. Also building a manometer seemed like something fun to do. See above...

On the plus side, I now know for sure that there's no problem with either the hose or disconnect.
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Old 07-01-2012, 04:36 PM   #5
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Gas Pressure Testing With Manometer


hvac benny,
By dial test, am I correct in the assumption that you're referring to the following:
1) Finalize appliance connections.
2) Pressurize the system to working pressure.
3) Connect a manometer to a gas output, such as a stove/grill burner.
4) Close shutoff valves to isolate the system (or at least the appliance) from the pressure source.
5) Confirm that there's no leak shown by the manometer in a reasonable amount of time.

Given how little good information is out there on gas, I like to confirm all assumptions like this.
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