Are you sure your nitrogen braze purge is clean? Look at this...

[hvac5646]

http://www.abbottwelding.com/index.p...urity%20Levels

Soda fountain CO has less H2O than some of these classifications.

Which one does your supplier sell you?

[hvac5646]

The suppliers I called did not know the purity of their own Nitro.

Called a national chain gas supplier an HE said they sold all industrial grade to HVAC houses in MI.

You guys might as well switch over to industrial CO2 if that is the case. It's drier.

[Greend88]

So industrial Grade has roughly 16 ppm water vapor in it, while the atmosphere on average has 2500 ppm, And With oxygen the nitrogen bottle has 10 ppm while the atmosphere has on average 209,460 ppm. That 16ppm and 10ppm hasn't caused any known problems that I'm aware of, While industrial grade CO2 has average 32ppm water vapor...http://www.abbottwelding.com/index.p...urity%20Levels I'd Stick with Nitrogen and a Deep Vac considering CO2 has twice the water vapor according to abbott.

[hvac5646]

That is not the table I was getting my info on Co2.

Seems the purity levels vary by mfg. The Airgas table we have shows 15ppm for their CO2 welding gas.

Airgas shows their bone dry co2 as a Cat IV while Abbott calls it a Cat III.

[air1]

Daikin says to use "dry nitrogen". When I asked the supply house guys if the nitrogen was "dry", I got a blank stare and they said "huh?".

[Greend88]

So what does your purity sheet show for Nitrogen from airgas?

[hvac5646]

Don't use nitro. I looked for it but could not find it on Air gas. But even if THEY have a grade that is close to what I posted you are still more cost effective using co2.

I raised this question cause there seems to be no firm consensus on what we call "dry". So my point is with so many grades of co2 dryness that don't seem to agree, how do we know what we are getting ?

[Greend88]

Id say use whatever your comfortable with. When it comes down to it we just want something that will prevent copper oxide from forming. whatever inert gas that works and is cost effective you can use. A small ppm of oxygen isnt gonna be enough to cause any problems nor is the few ppm moisture content. your vaccum pump will remove all that and the dryer will catch any thats left.

[hvac5646]

Don't use nitro. I looked for it but could not find it on Air gas. But even if THEY have a grade that is close to what I posted you are still more cost effective using co2.

I raised this question cause there seems to be no firm consensus on what we call "dry". So my point is with so many grades of nitrogen dryness that don't seem to agree, how do we know what we are getting ?

Edit: Meant to say nitro not co2 dryness.

[Chuck]

I use nitro, its what the co. buys me to use. What's the big deal? Use whatever you like.....

[hvac5646]

I use nitro, its what the co. buys me to use. What's the big deal? Use whatever you like.....

For you and and other guys who use co supplied nitro it's a moot point.

But those of us who are responsible for our own materials, CO.2 is the better bet cause you get approximately 3 to 4 x the amount of gas in the (close to ) same size tank than you would with nitro. And Co2 cost less.

A lot of friends, and posters here, have complained about running out of nitrogen
on a busy day or a big job. Which would you rather carry?

An aside:
The MBK 6 using a flow meter runs out of gas when brazing up a four ton evap and line set with a flow rate of 5 sftf.

[ga-hvac-tech]

So industrial Grade has roughly 16 ppm water vapor in it, while the atmosphere on average has 2500 ppm, And With oxygen the nitrogen bottle has 10 ppm while the atmosphere has on average 209,460 ppm. That 16ppm and 10ppm hasn't caused any known problems that I'm aware of, While industrial grade CO2 has average 32ppm water vapor...http://www.abbottwelding.com/index.p...urity%20Levels I'd Stick with Nitrogen and a Deep Vac considering CO2 has twice the water vapor according to abbott.

Looks to me like we are splitting hairs...

Reducing water vapor by 99.36% and reducing O2 by 99.9948%... well that is close enough for work outside a chemistry lab (Used to do maintenance for a chemistry lab... know how procedures are done there).

Anyone know of any test results where less than 1% of water vapor or less than 1/100 of 1% of O2 would make a difference? Be interesting if anyone has even run that test...

[hvac5646]

Looks to me like we are splitting hairs...

Reducing water vapor by 99.36% and reducing O2 by 99.9948%... well that is close enough for work outside a chemistry lab (Used to do maintenance for a chemistry lab... know how procedures are done there).

Anyone know of any test results where less than 1% of water vapor or less than 1/100 of 1% of O2 would make a difference? Be interesting if anyone has even run that test...

The h2o content is emphasized because we use gas to sweep the system between evacs and blow out impurities. The less h2o the better.

[jtrammel]

The h2o content is emphasized because we use gas to sweep the system between evacs and blow out impurities. The less h2o the better.

A deep vacuum will remove the minute amount of h2o.

[hvac5646]

A deep vacuum will remove the minute amount of h2o.

You want to add time to your evacuation? If you are not concerned about the moisture content of your purge gas than you are disregarding every lesson ever taught on evacuation and system de hydration.

[jtrammel]

I don't want to add time, although there is usually plenty to do while pulling a vacuum. I don't have an inert gas moisture meter so I have to trust what the supplier gives me.

[hvac5646]

I don't want to add time, although there is usually plenty to do while pulling a vacuum. I don't have an inert gas moisture meter so I have to trust what the supplier gives me.

One good test I learned is to release about 75psi thru a 1/4 hose and let the gas hit a mirror. If it leaves behind a film or residue there is oil and an undesirable amount of moisture in the tank. Than you have to run your gas thru a filter drier or take the unpure tank back.

[ga-hvac-tech]

Remember that how deep a vacuum goes and how well it holds is a measure of dryness.

Most of the time a single pass with the vacuum pump draws the system down to around 200-225... and it rises to less than 400. Now that is a good vacuum for residential work... even 410. If it is stubborn... a triple evac will allow me to go below 200 with a rise to less than 300 if I wanted to do so.

Now I fully realize in refrigeration work deeper vacuums are desirable, and sometimes necessary.

In residential work... the difference is negligible.

Experience... many years (in my case decade +) and probably over a thousand systems opened and closed... teaches one what is necessary ans what is splitting hairs.

[Chuck]

One good test I learned is to release about 75psi thru a 1/4 hose and let the gas hit a mirror. If it leaves behind a film or residue there is oil and an undesirable amount of moisture in the tank. Than you have to run your gas thru a filter drier or take the unpure tank back.

It better be a brand new hose, otherwise the residue could be from what was in the hose. Even a brand new hose could have oil residue left in it from the manufacturing process.

[GT Jets]

I think this discussion went way off track.

The OP mentions purge, not evacuation.

Purging with nitrogen is to "displace the oxygen during the brazing process", you have to realize that the moisture content is pretty much irrelevant in most of our uses.

Co2 in the meantime causes condensation because it is in a liquid state when released and that change of state can cause WAY more issues than static moisture in "dry nitrogen". Nitrogen is in a gaseous state and does not cause the condensation issues.

So what's the argument? Because dry nitrogen should not be used because it is not lab quality? Give me a break.

Something to realize too, the molecular structure of nitrogen is a bit larger than that of o2, this incompatibility is where the moisture discussion becomes moot.

IMHO using CO2 will cause more problems than they will eliminate.

Unless of course CO2 is indeed the refrigerant being used... Then of course the action changes. Nitrogen also does not convert as much as carbon dioxide does when brazing temperatures are realized. If you really want to get trick, use argon.

GT