Nitrogen while brazing opinion

[tecman]

When brazing with a nitrogen purge, I always try to have the nitrogen exit the fitting that I am brazing. My feeling is that minimizes the possibility of heat damage to the gas hose and it also helps carry heataway from the work area.

Anybody purge "into" the brazed joint ? Are there any opinions on the methodology ? Anybody see any other pros/cons to other ways of doing it ?

paul

[docholiday]

I wouldnt suggest trying to use the nitrogen to cool the fitting. The primary purpose is o dplae ny oxygen in the line that allows for scaling inside the pipe when the heat is applied. You should not try to pressurize the line. I would say purge it then reduce the flow to a minimum which will simply prevent the oxygen from returning. Take a schrader out and allow it to flow slowly but unobstructed.

[tecman]

Originally posted by docholiday
I wouldnt suggest trying to use the nitrogen to cool the fitting.

Just to clarify, I do not use the nitrogen for cooling, but I have just felt that carrying the heated nitrogen out of the tubing at the work area was better than having the hot gas circulate through other parts of the system.

Frankly I never remove the schrader valve, but just set the regulator to give me a nice steady, low flow while pushing through the schrader. Just one less step for me.

paul

[RoBoTeq]

I do the same this most times, but purely out of habit of "feeling" it is best to let the heated nitrogen exit the system immediately. I've never seen anything indicating that it really does make a difference but it does seem like a common sense thing to do.

[docholiday]

OK, I may have misuderstood... Thanks for clarifying.

What about when your brazing the indoor coil in? How do you deal with it there and why is it not a problem there? I suspect too as Robo and you feel that its a gut instinct thing that suggests that the heat is damaging but rest assured, the heat is considerably lower than the actual brazing temps and not a problem. I do see how it can make you think twice though.

[smokin68]

As long as there's nitro running through the brazed joint everything should be fine. I do remove the schrader's though as it only takes a second and prevents them from heating up and possibly leaking. this is just something I do though.....alot of people I've seen never run nitro.

[troyorr]

Why don't you purge with nitrogen like the manufacturers recommend as well as how the industry recommends ? I can't understand why we still have "professionals" trying to shortcut or improperly perform a task. What harm can heated nitrogen do to a system? I've used heated nitrogen to purge and dry crogenics tanks with no problem at all.

[tecman]

Originally posted by troyorr
Why don't you purge with nitrogen like the manufacturers recommend....

I agree, but every install sheet I have ever seen only states something like "flow nitrogen at 2 PSI while brazing..."

The only point I asked is if there are any preferences to the specifics of how different people do it, and if there is any real advantage of one way vs another. The basics of how and why nitrogen is used is clear, just is there perhaps a better way so we can all improve our methods.

paul

[troyorr]

tecman, to protect my hoses, I fabricated a 12" piece of 1/4" copper with a flare fitting on one end and a male 1/4" fitting on the other. This lessens the potential of heat destroying my hose seals. I still wrap the fittings with a wet rag too. I make up all of fittings and joints to be brazed and then adjust my nitrogen flow so I just feel a slight pressure against my hand. If the nitrogen is flowing while you braze, very little heat will actually be picked up by the gas. You don't want too much pressure because you could actually force nitrogen out of the joint you are soldering, resulting in a bad braze. By removing the schrader cores, you prevent damage to the seals and you allow the nitrogen to flow easily and freely. Remember, everyone will find their own way to perform this task. The only constant that everyone should comply with is to actually use nitrogen whenever they braze.

[GradyWhite244]

I too use a piece of 1/4" copper & wet rag. I don't know about now but York used to specify in the installation instructions to allow nitrogen to continue to flow until the joint had cooled completely. Years ago I got into the habit of doing that & still do. Go thru a lot of nitrogen but it's cheap & no air/moisture will be drawn into the lines while cooling.