If you let the cylinder set for a day and then attempt to use it again,
can you now get decent pressure again and a decent flame? If so,
then the problem is the fact that you are drawing the MAPP too long
and too fast. The liquid in the cylinder is evaporating as you draw off
gas, and this evaporation cause the same cooling effect that we get
with refrigerants in an AC system. The cooling effect is considerable
and the liquid inside the tank does not warm up as quickly as you
may believe when you feel the side of the cylinder.
You can pause and warm the cylinder - remember that you need to
immerse it in warm water and swirl the liquid that is in the cylinder.
Watch an HVAC guy as he pumps refrigerant into your AC system -
he has the same tank pressure drop problems and uses the same
method to warm the liquid inside.
You can also purchase a second MAPP torch. They aren't that
expensive and this is a very easy fix. Now you can alternate between
two torch setups, allowing one to warm up while you are using the other.
People keep giving me their old torch kits and propane bottles plus
I find them cheap in garage sales. I've got at least 6 or 7. Sometimes
I'm warming the work with MAPP hooked up to a "turbo-torch" while
my son or wife is also holding a second propane flame on the work.
Plus I've got another MAPP tank and torch ready if needed. Obviously
this is for larger tasks.
Depending upon your applications, there are other ways to attack
1) Consider a "turbo-torch", which provides a hotter flame through
more efficient fuel-air mixing. You'll heat the work better and
faster and use less fuel, hence cooling the MAPP cylinder less.
2) If you are brazing, you can switch to more expensive, lower-temp
brazing materials. One example is the class of silver brazing
alloys. These cost more, but save you time, fuel and oxygen
(if you are using O2).
3) For some applications, you can use MAPP and oxygen. But for
the average person, this is costly. Those small disposable tanks
of oxygen don't hold a lot of gas and the unit cost is extremely high.
Even the small refillable oxygen tanks are very expensive to refill on
a gas volume basis. (I do encourage serious DIY types to consider
oxygen-gas cutting, brazing, and welding. You feel more self-
sufficient and you can become very popular in your neighborhood.)
I've got a question about using those small yellow cylinders of MAPP
gas. It seems that I can only use one until it is half empty. Then the
pressure drops off to the point that the flame won't stay lit. I've
tried tipping the cylinder in all directions and I'm using it indoors so
the cylinder is warm. What am I doing wrong in using it?
This has happened with other cylinders in the past, by the way.
Thanks for the plumbing help,