MAPP gas usage problem

[Mark Witczak]

Hi all,

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, Mark

[Gideon]

Mark,

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 this problem:

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.)

Good luck, Gideon

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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, Mark

[SQLit]

As a WAG, are you using a self ignition torch head? If so try a old brass head with just a knob.