Gas system maintenance
Threaded parts seldom seal gas tight; especially when exposed to full cylinder pressures, in the case of most cylinder-mount propane torches. The common fix is to use gas rated Teflon tape, but such tape is meant for relatively low pressures encountered in household natural gas lines. So, Teflon tape is not likely to work well on lines without a pressure regulator installed. Even then, they must be turned in the right direction to avoid unraveling during installation, and the tape must be kept away from the last two pipe threads to avoid Teflon shreds from migrating into the gas line; inevitably plugging up the gas jet.
A surer method is to apply gas rated gasket sealant on the threads of the male connection (kept away from the last two threads on the fitting’s end). If you disassemble the fitting later, be sure to thoroughly clean all traces of the sealant from threads first thing, lest some end up inside the gas line. You can also employ gas rated thread sealant (AKA Thread-locker).
Always clean the gas system before assembly: Teflon shreds are not the only junk that can enter your gas system. Burrs from cutting, grinding, sanding and threading operations must be thoroughly cleaned from the work pieces, and all lines and hoses cleaned out with compressed air, to avoid debris from accumulating in the small gas orifice of a burner. Debris could have collected in the fuel hose from the gas cylinder, if you rent cylinders from an exchange system, from junk in the hose, if you leave it off for a long time. Insects and spiders are attracted to fuel hoses, because of their stench of fuel vapor. Propane can leave a buildup of tar and wax in a burner's gas orifices; especially from really poor quality fuel. The wrong kind of hose fuel will rot out over time; only use propane rated hose.
Pressure test the gas system before use: Use liquid detergent in water to pressure test all joints on any gas assembly, starting at the fuel cylinder, and checking every joint including those in the burner. Some burner designs can tolerate minor leaks in the gas jet parts, by drawing them into the mixing tube along with incoming air; other designs will backfire from the smallest gas leak.
Caution: Normally the gas pressure within a burner is a little less than line pressure, due to its open gas orifice. But a plugged orifice will allow full line pressure to accumulate in all parts; without a pressure regulator (such as with cylinder mount torches) that will reach full fuel cylinder pressure; this can be well over 150 PSI. The very small orifice sizes used in small air/fuel torches are given to clogging from impurities found in propane fuel. Keep a set of torch tip cleaners on hand to clean out clogged gas orifices immediately.