Teflon tape is designed to act as a lubricant on pipe threads where
the seal is developed on the thread not the face of the joint this
is the type of joint used in plumbing and natural gas lines or
propane lines in a house for example.
Do no use teflon tape on any fittings for standard regulators, hoses
or torches. all of these fittings are designed for a metal to metal
seal. If you look at both halves of a fitting you will see one side
has a conical or hemispherical shape and the other side of the
fitting will have the negative form of that shape. These are the
sealing surfaces of the fitting they are designed to be brought
together in firm contact by the threads on the fasteners. If either
of those faces is scratched up or distorted in any way then they
will not seal properly. Adding teflon tape to the threads will not
improve the ability to seal as the threads are not what creates the
seal and it is likely you will get some teflon between the sealing
surfaces and make it impossible to get the metal to metal seal. It
is also very possible that over time as the joint is taken apart and
put back together that some teflon will get into the inner parts of
the hoses and regulator which could cause operational problems with
the regulator . If you can’t get a seal on these type of fittings
there is a problem, take it to your gas supplier and ask them to
check it out for you. Acetylene and oxygen tanks are often used on
construction or industrial sites where they are not very well
treated and can often have damaged sealing surfaces on the valves
due to rough treatment. So inspect the sealing surface when you
receive the tank from your supplier if it looks damaged don’t accept
it or send it back.
Jim