The Smith Little Torch and Compressed Air
Q: I have a Smith Little Torch, and I wonder if I can run it on propane and compressed air, or even by blowing with my mouth. An old jeweler friend said it should be possible.
A: I think your friend is wrong. I’ve never seen a Smith Little Torch run with compressed air. Always, they’re set up with oxygen and some fuel gas. The design of the tips, a straight single orifice, isn’t well suited to compressed air. It might work with a very fast-burning fuel like hydrogen, or perhaps acetylene, but even then, I’d rather expect it to not work well, if it did work. The problem is that combustion with compressed air is not aggressive enough, and given the speed with which any burning action progresses through a gas stream; in fact it’s slow enough so that with any decent gas flow through the tip, the gas-air mix flowing out would be moving faster than combustion could travel back along the gas stream, so it would blow out. Tips for compressed air generally utilize a multiple orifice design that uses a wider head with more orifices and more cross-sectional area to the flame, which slows the gas down before it exits, so the flame can keep up and stay on.
Another consideration is that even the largest tip on the Smith Little Torch is quite small. The tiny flame you get with it needs to be quite hot to be at all useful for soldering or working metal. You’ll find that with compressed air, even if you get the tip to stay lit, there’s just not much heat there. An oxygen/fuel flame is much hotter, which makes those small tips a lot more useful.
Bite the bullet and get an oxygen tank. You’ll find that the Little Torch, due to its very small tip sizes, uses oxygen very slowly, and even a small R-sized tank will last a long time. I’d recommend a larger tank, like a 40 cubic foot one, however, since the tank costs a bit more, but not in proportion to the cubic feet it contains, and the refill on the larger tank is not much more than the refill cost of a small one. But a 40 cubic foot tank, running just a single Little Torch, even quite a lot every day, might easily last you many months, or even a year. The economics of this makes the cost for the refill rather trivial in the end.
If you wish the type of control over the flame often found in European workshops, where torches are fed just fuel gas, and mouth-blown, then you need the type of mouth-blown blowpipe torch that’s designed for that type of fuel. They’re highly versatile tools, they take a bit more practice to master. Few people in the U.S. use them, but in Europe, they’re what a lot of smiths learned with, and in the hands of someone who’s used to them, they’re very good tools, and cheap to run. They generally cost less than a Little Torch setup. The same basic torch design, but with an additional valve to control air flow, is what’s used with compressed air.
by Peter W. Rowe M.F.A., G.G.