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View Full Version : Can we use dry air for leak testing of Refrigeration system







sagar45
03-01-2015, 01:42 PM
We want to use dry air for leak testing of refrigeration system .

Can i get information regarding the air drier and dryness fraction required.

We are going to replace nitrogen which are we using today.

Please guide.

install monkey
03-01-2015, 02:53 PM
fill the system with soapy water and look for bubbles
or alternativly
http://www.epa.gov/greenchill/downloads/RealZeroGuidetoGoodLeakTesting.pdf

The Viking
03-01-2015, 04:20 PM
Looked in to this in the past,

The air required is to the same specifications as a scuba diver would use with Nitrox mixtures.
Unfortunately in real life that is more expensive than OFN...
And, OFN will draw moisture out of your system making the vacuum cycle shorter whilst dry air won't.
Further more, you are likely to need OFN on site anyway if you are doing any brazing so why carry 2 different gasses when 1 will do?

:cool:

monkey spanners
04-01-2015, 01:06 AM
One of my customers has their own nitrogen manufacturing plant in their factory, might save soem money if you are in a manufacturing environment.

glenn1340
04-01-2015, 11:25 AM
You could produce dry air on site using an air compressor with good quality filters downstream (or even an oil free machine) along with a regenerative dessicant dryer. This should give you a dew point of at least -50c or even lower. The advantage this would be if a leak was present you wouldn't have to let the expensive nitrogen out and refill to test again.You`d then purge with OFN. Obviously you wouldn't be able to reach the higher strength pressures of 410a unless you had a high pressure compressor and dryer but for initial leak tests on a large system it could be an idea. You`d have to have all that already kit set up, possibly on a small trailer, so as to enable you to hook it up easily; so for small systems it`s not economical but for regular use on complex pipework systems it could save time and money.

Grizzly
04-01-2015, 12:27 PM
Hi Guys.
Am I missing something here?
Are we really condoning using air as a leak check medium?
There is a must be good reasons air which is the most plentiful and easiest to work with gas on the planet has/ is not used already.

I am not a chemist so I cannot describe the molecule ratio ect.
But every bit of training I HAVE EVER HAD says do not use compressed air to leak check.

Now because someone in India wants to cut corners and save Money. "We" are trying to help them!
What happens when someone thinks Ah! I could use that bottle of Oxygen that I have handy instead.
They kill someone, themselves or both?

Madness!
Grizzly

Rob White
04-01-2015, 01:10 PM
.

Nitrogen is inert and therefore does not react with anything.
Oxygen is a reactor and therefore it is dangerous to use as
a testing gas. Oxygen reacts with oil and can become explosive.

Air is part oxygen so there is a very, very slight risk when using air
under pressure with oil.

The reason why we use oxygen free nitrogen (OFN) is firstly OFN
is inert and does not react, but another is it's ability to attract moisture.

Moisture is H2O and for some chemical reason oxygen is
more attracted to nitrogen than it is to hydrogen so if oxygen comes
into contact with pure nitrogen it gives up it's bond with hydrogen and
combines with the nitrogen.

When the nitrogen is vented it takes the oxygen molecule with it and
if you take the oxygen away from the hydrogen it stops being water.

Regards

Rob

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Grizzly
04-01-2015, 02:30 PM
.

Nitrogen is inert and therefore does not react with anything.
Oxygen is a reactor and therefore it is dangerous to use as
a testing gas. Oxygen reacts with oil and can become explosive.

Air is part oxygen so there is a very, very slight risk when using air
under pressure with oil.

The reason why we use oxygen free nitrogen (OFN) is firstly OFN
is inert and does not react, but another is it's ability to attract moisture.

Moisture is H2O and for some chemical reason oxygen is
more attracted to nitrogen than it is to hydrogen so if oxygen comes
into contact with pure nitrogen it gives up it's bond with hydrogen and
combines with the nitrogen.

When the nitrogen is vented it takes the oxygen molecule with it and
if you take the oxygen away from the hydrogen it stops being water.

Regards

Rob

.

Thanks for the knowledgeable Answer Rob.
Grizzly

PaulZ
04-01-2015, 11:13 PM
Hi Grizzly
I am with you on this matter, I was taught to only us Nitrogen to test. In years gone by I have seen compressed air used on NH3 systems but I personally don't like doing it.
Regards
Paul

glenn1340
05-01-2015, 05:02 PM
Ok let`s take a step back here and look at what I`m suggesting here. Basically we`re using super dry oil free air to check for leaks on some pipework, that`s not brain surgery. After that we could carry on with higher pressures purging etc with OFN
I worked on lubricated screw air compressors for years for thirty odd years and have never had any problems with compressed air mixing with oil vapour and that was at temperatures up to 100c. Now, the reason it`s probably not used is the cost of setting up the equipment and getting it to the point of use.

chemi-cool
05-01-2015, 08:26 PM
I have received a few CO2 tanks from Tomco Usa that came with dry air in the refrigeration unit. Purged with onf, vacuumed and charged with refrigerant and all is well for over 10 years now.
But... the issue is different, air has big molecules, larger then refrigerants so you might not find all the leaks, Helium is the best leak finding agent as it has very small molecules and if your system is helium tight, you are safe.
Ofn is cheap, high pressure agent for a leak test.

piewie
06-01-2015, 01:00 PM
OFN is the way to go! But if you order a new performance tested compressor, guarantee it was tested using air!

Rob White
06-01-2015, 02:55 PM
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I have worked with high pressure air for many, many years.
Air well in excess of 200 bar and for the last 10 years or so
the air is enriched with oxygen.

Oxygen enriched air needs to be in oil free environments but
air just needs to be in a cleanish environment.

So I think the practicalities of using air, are the main reason
why it is not done. If you are in a workshop and if you have
access to good quality clean and dry air, I don't see any real
issue with it, but out in the big world you would need more than
one cylinder and more than one gauge/regulator and if you
forget which is which one day and you braze with air purging
then your warranty will be gone......

Regards

Rob

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