I'm just going to add a few more details to what has already been written using propane with an oxygen concentrator for brazing. Now that I've had this setup for about a half year I can give some more refined observations. I've been amazed at how much longer and cheaper my BBQ bottle of propane lasts compared to acetylene. I have a fairly big acetylene tank that costs me $35 to refill. During those 6 months I've taught 3 classes with 3 students in each class (with Herbie as my assistant). 5 students have used propane and the other 4 acetylene to practice and build their frames. We gave our multiple demonstrations in propane. I've also done my own work between classes with propane. I've had to change acetylene tanks but my propane tank (which costs me $18 to refill) is only down less than half way.

I found that turning the propane line pressure down to 2 psi (instead of 4 or 5 previously) makes it easier to keep the flame attached to the tip when the propane is turned up before oxygen is added. I still seem to get plenty of oomph in the flame at that line pressure after the final adjustments with oxygen.

Ordinarily lighting a propane flame is a 2 step process to keep it from separating from the tip or blowing out. Only a small amount of propane can be initially turned on when lighting the flame. After it is lit, it can only be turned up so far before it separates. I start to add oxygen before the flame separates. I watch the end of the inner tip until the very end starts to turn a bit yellow/orange. That is about the right adjustment for propane and then I can turn up the oxygen to match. Usually the right gas balance is when the flame starts to turn from a greenish color to a more bluish. You can get a feel for where a neutral flame is by adjusting the oxygen back and forth and watching the flame color change a little from a greenish hue to a bluish one. You've got it right when it is in the middle of those colors.

As I learned from mattsummers post, it is not possible to tell how much propane is left in the tank by looking at the tank pressure gauge. I went to Lowe's to find a gauge that indicates how much propane is left in the tank (I tried at the local hardware store first). It cost me about $12. I attached this new gauge to the propane tank and my Victor regulator to the gauge mount. They both have 510 G fittings. It takes some seconds for the gas to get through the gauge before the regulator gauges pop open.

I will mention again that when I am using the oxygen concentrator, I have to turn it on a few minutes in advance so its internal bladder can fill and purge the line so only oxygen is coming out. I have to open the knob on the torch to let the oxygen pass through or the machine will beep saying Grandma isn't getting air.

Doug