Mapp Gas Or Oxygen-Acetylene Brazing?
One of the choices that any HVACR service company has to make is whether to supply their trucks with expensive oxygen-acetylene brazing rigs or Mapp gas torches, for each has its own unique advantages.
Mapp gas (a high-temperature mixture of petroleum byproducts) comes liquefied in compact canisters, which allows torches to operate for several hours, and some of the new instant-start brazing tips are quite inexpensive and very easy to use. Also, the gas canisters can be purchased locally at almost any hardware store. So they definitely have their place in HVACR service trucks, if for no other use than an emergency backup.
Oxygen-acetylene rigs, on the other hand, are usually about six times more expensive than their Mapp gas counterparts. They are bulky, heavy and unwieldy; the gas at startup creates a lot of soot; the gases cannot be liquefied so they don’t last as long; and refilled containers are usually not available in hardware stores. However, the flame they produce is much hotter. So at first glance, the Mapp gas solution looks much better to many contractors and technicians.
However, the hotter temperature of the oxygen-acetylene rig is a very important factor that should not be overlooked.
It isn’t that the heating properties of Mapp gas itself are the problem, but the lack of introduction of pure oxygen into the flame. And the resulting introduction of inert gases from the air into the flame creates a larger, less concentrated, and cooler burn. So combination Mapp gas-oxygen rigs (where available) are very desirable due to the longer burn and ease of product availability.
The problem with the larger, cooler flame common to standard air-Mapp gas rigs is: Not only is it limited to brazing smaller components and smaller copper tube sizes, but it takes longer and results in more heating of the surrounding area, which does more damage to heat-sensitive parts. Also, it creates more copper-oxide corrosion than a smaller, hotter flame. So, I don’t recommend Mapp gas-air brazing of such devices as heat-pump reversing valves, filter-driers and compressors.
Several years ago, I used to see a rig available at hardware stores that used Mapp gas and Solidox pellets, which created a hotter burn. However, I haven’t seen the combination available lately, probably due to its use by terrorists in making compact bombs. And if it is still available, compressed oxygen is probably less expensive and more effective anyhow.