Margaret, It sounds to me that you have not properly adjusted the
valve on the regulator that controls the flow of gas to the torch
When you use a tip with a small oriface, the valve should be backed
partially out so the pressure does not blow the flame out. However,
when you change to a larger tip, you must turn the valve in almost to
the stop so you get the required pressure. The reason the flame
starts out strong and then shrinks is …there is pressure built up
in the hose when the torch is turned off but after opening the torch
and lighting it, the gas burns off and there is insufficient pressure
to keep it lit.
The Smith torch is engineered to give you a nearly perfect flame
just by using air instead of 02. In this case, as the pressurized
gas flows past the holes in the base of the tip, ambient air is
sucked in. As ambient air contains approx 20% 02 it mixes with the
proper amount of gas to burn at a hot even flame. If you turn down
the gas flow at the torch head, there is less gas but the lower
pressure will not pull in the right amount of ambient air. These
torches should always be used at full open (I don’t mean all 5 turns
of the knob…one full turn is the same as 5 in this case).
If you want more heat, use a larger tip, open the regulator valve by
screwing it in full, and open the knob on the head one full turn.
If that does not result in a full hot flame, have your local welding
supplier check the torch head…the filter system inside the body
of the torch may be blocked.
Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut2