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Old 04-13-2010, 11:18 PM   #1
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Pressure Testing Gas Line


Hi everyone, wondering if anyone had any insight here. I just had some gas line installed by a plumber. When he finished he put air into the line (25PSI). A day later the pressure has dropped to (11PSI). He mentioned it should be anything to worry about because air changed and expands based on temp and he also mentioned that his valve maybe leaking. So my question is does that make much sense? If the PSI is dropping doesn't that mean there is a leak in the system and when gas gets connected isn't it going to leak out as well?

I think the local inspector uses 5PSI for 24hrs for final inspection.

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Old 04-13-2010, 11:27 PM   #2
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Quote:
So my question is does that make much sense?
Uh, no. First, if he thinks his valve is leaking, he needs to verify that, correct it, and retest. Then, as I am not a fitter, I could not tell you the allowable drop of pressure based on the ambient temp but if the inspector only allows a 5 psi drop in 24, then your system cannot drop more than 5 psi in 24 hours. The fitter needs to so what it takes to meet those requirements.

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If the PSI is dropping doesn't that mean there is a leak in the system and when gas gets connected isn't it going to leak out as well?
if it is only what the fitter claimed, no. Air does expand or contract based on the temp of the air. If he charged the system at the end of a hot day and the following day (24 hours later) was not similarly hot, there will be a lower pressure reading simply because of the reduced air temp. and of course, if the leak is his valve, then as that will not be there when your system is complete, no leak there.

if he charges the lines when it is cold and then it gets really hot the next day, the pressure can actually go up. As I said, I do not know how to calculate of guesstimate the allowable loss or gain. Hopefully one of the other guys around here can be more accurate with how much loss based on temp would be expected.



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I think the local inspector uses 5PSI for 24hrs for final inspection.
then the fitter needs to be able to show that and as it stands, he obviously can't.

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Old 04-14-2010, 05:14 AM   #3
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Pressure Testing Gas Line


Gas lines need to be tested at 2.5 x the working pressure so never more than about 5lbs for residential gas. Gas lines must hold pressure forever. There should be no more than a couple inches WC change due to expansion. Any valves, fittings or gauges that leak need to be replace and the system needs to be re-tested. Hard to believe that a licensed plumber would be that casual about a gas leak.
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Old 04-14-2010, 07:32 AM   #4
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Pressure Testing Gas Line


Was the guy licensed ? He should know that losing pressure is not acceptable. did he pull a permit? Is the city going to inspect it? This is a safety issue your family lives there not the plumber
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Old 04-14-2010, 09:01 AM   #5
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Pressure Testing Gas Line


Yup he is licensed and permit is pulled waiting for inspection. Thats what I figured if the valve is faulty common sense to change the air valve. I'll update on inspection.
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Old 04-14-2010, 09:17 AM   #6
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Pressure Testing Gas Line


I guess it won't pass inspection then.

Usually the air valve leaks around the needle. We solve our leaking valves by either changing the needle, or putting a valve stem cap from the truck on it if we don't have a needle.

That shouldn't be acceptable by any standard that I can think of. If there's a leak, you figure out what it is and you get it to stop, even if it's only your test equipment.
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Old 04-14-2010, 10:37 AM   #7
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Pressure Testing Gas Line


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...air changed and expands based on temp...
Based on the old chemistry formula PV=nRT (and remember T is in Kelvin),
if the air had a temperature of 120F when he pressurized it to 25psi (let's allow for some heating of the air by the compressor), and you read the temperature the next day when it's 50F out, the pressure would have dropped to 22psi from the change in temperature.
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Old 04-14-2010, 10:53 AM   #8
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Pressure Testing Gas Line


Does anyone typically know what the process is when an inspector comes over to check the air pressure? I mean the pressure has been dropping over 24hrs and unless he is there for awhile he won't know if the thing is holding pressure or not.

I figured that a huge drop means leak. Can't understand why he wouldn't replace his valve if its faulty.
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Old 04-14-2010, 12:31 PM   #9
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Pressure Testing Gas Line


Read the meter before you go home tonight. Come back tomorrow and read the meter. Pressure lower? Test has failed.
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Old 04-14-2010, 01:10 PM   #10
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Pressure Testing Gas Line


Quote:
Originally Posted by cloves View Post
Yup he is licensed and permit is pulled waiting for inspection. Thats what I figured if the valve is faulty common sense to change the air valve. I'll update on inspection.
The point is that it's too late to find out (if all the reasons that the "plumber"? gave for the significant air leak were correct) when you already live in the house!!
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Old 04-14-2010, 08:24 PM   #11
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Pressure Testing Gas Line


It's supposed to hold pressure for 15 minutes. I'm not sure why it's like that. Whenever we test, we test in the AM, do some pick-up/clean-up work and 6-8 hours later if it's still holding, then we call in the inspection.
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Old 04-14-2010, 08:41 PM   #12
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Pressure Testing Gas Line


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It's supposed to hold pressure for 15 minutes. .
15 minutes? Wow, I've never seen a test less than 24 hours.

and in this situation, the OP even stated he believes it to be a 24 hour time.
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Old 04-14-2010, 10:03 PM   #13
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Pressure Testing Gas Line


I will find out tomorrow how long the test is. You know the problem with some towns and inspectors is that they don't give 2 shakes. Plumber was telling me that sometimes they just show up and are gone in 5 minutes. Cities just want money half the time imho. Not all inspectors and not all cities but that's the reality of the real world.
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Old 04-15-2010, 09:08 AM   #14
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Quote:
Originally Posted by cloves View Post
I will find out tomorrow how long the test is. You know the problem with some towns and inspectors is that they don't give 2 shakes. Plumber was telling me that sometimes they just show up and are gone in 5 minutes. Cities just want money half the time imho. Not all inspectors and not all cities but that's the reality of the real world.
It depends on the plumber and the inspector. If you have a good working relationship with them, there's not a lot of reason for them to spend half a day waiting for the pressure to drop if they already know you do good work.

For example : I was testing a gas line one morning, had already scheduled inspection, and the inspector showed up about 5 minutes after I had discovered a leak. I told the inspector right up front that it was leaking and that we'd have to order a new part to fix it. The inspector went ahead and gave me the sticker because 'it would be a waste of gas money and time to come back out here. I know you'll fix it right and test it yourself anyway' (which is exactly what I would have done if it was or wasn't getting inspected) We don't jerry-rig things and we don't try to slide stuff under their nose. They know this.

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