I ran a new gas line for a garage furnace.
It is about 50 foot of 3/4 line
I pressure tested with air at 30psi to find major leaks.
I soaped all joints and did not see anything.
It dropped to 28.5psi in 24hours.
From what I have read the normal test is 10psi for 10-30min with no
I am now going to let it sit at 10psi and see when/if it drops.
Any other suggestions?
I am having problems with the unions leaking.
Thats probably why I had the pressure drop.
I jacked the pressure up to 50psi and saw the unions leak.
I found one had pits in the sealing surface - I replaced it.
The other has a very small leak with 30psi or higher. I tightened the
snot out of it.
No leaks at 10psi.
I will check for a drop in the morning.
That's why I use dry nitrogen for all my pressure tests.
Whenever I do an HVAC install with my friend, we're
usually having to test the refrigerant line set as well
as the gas line so we just use nitrogen for all of it.
In the summertime the air is indeed very humid here in
Alabamastan. I like dry nitrogen because it is inert
and has no effect on any of the materials I'm using.
For Freon lines it's a no-brainer but a gas line with
a little bit of moisture mixed with any trash left in
the line can clog a screen in a gas valve. I have seen
the screens in gas valves look like someone poured the
contents of a vacuum cleaner in them. With high pressure
nitrogen I can blow the line out, leave a suitable amount
of pressure in it because the pressure I use for testing
refrigeration lines would damage a gas valve. If we ever
install lines out on a new construction site, it could
be weeks before any equipment is set/installed outdoors
so I like being able to walk up, put my pressure gage
on a fitting and the pressure on a good line never seems
to vary outside the tolerance of my gage. If put 150psi
of nitrogen a line set and there are no leaks, I'll read
150psi a week later with the gage I have. I'm sure that
a very precise laboratory instrument could measure the
difference but with my "crude" gage I don't see any.
IIRC the test the inspector wanted was 15 PSI 24 hours no leaks. With that
said, your pipe should hold 30PSI with no leaks.
As someone else mentioned you have to be aware of temperature changes.
Several things go on. First as a gas is compressed it gets hotter and
expands. Let it sit in a pipe in November and it will cool and shrink, so
it might be that your initial observation of 30 PSI was of warm air and your
second observation was of a cooler pipe full of the same volume of air.
I would leave it at 30 PSI for several days and make a note of the ambient
temps with the pressure observations.
Assuming you have natural gas, the service pressure is 11 inches of water or
a little less than 1/2 psig.
Also don't forget to check for leaks at the fill valve.
If knowledge is power, and power corrupts, what does this say about the
11 inches is a lot higher than Alabama Gas uses for standard
residential service. Whenever I've installed a NG generator,
the specs called for 11 IWC requiring the customer to request
a 2 pound pressure service from the gas company and the regulators
for all the other NG appliances are usually adjusted for 3-3.5
IWC. The older farts working in the field for the local gas
company have told me that the pressure on the typical 3/4" black
pipe supply line coming off the meter and going into a home is
around 6 IWC. If you were to connect 11 IWC pressure to most
natural gas appliances, the gas valve may go into a safety lock
out state. Many other gas companies will require a special
request from a customer for pressures higher than 5 or 7 IWC
going into their home.
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