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Old 03-13-13, 06:34 PM   #2
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For hobby or DIY (inexpensive) use, you have a few choices:
1. Blow torch bottles of propane
2. Cylinder exchange propane (BBQ grill tanks)
3. MAP/PRO bottles of propylene

Using option 1 or 2, you get HD-5 grade fuel propane. By the standard, it is at least 90% propane and up to 5% propylene. There is no higher standard in the USA for fuel-grade propane, so 99% propane and 1% propylene is still HD-5 grade. In reality, the gas in the bottles is nearly all propane and propylene, with a few ppm each of trace gases such as: butane, isobutane, cyclopropane methane, ethane, etc which varies by location. The propane industry works hard to keep nasty stuff out of their product. This includes water, air, acid, and generally anything not flammable and condensible.

For general-purpose hobby use, propane and propylene have very nearly the same properties in the refrigeration circuit, so a little propylene in the mix will not skew the performance of a unit. So as long as you charge slowly from the bottom of the bottle and run the exiting liquid through a filter-drier on its way into your system, you will be good to go. Just remember to stop charging before you run out of liquid in the bottle. The lighter gases, if present, will be in their gaseous state in the bottle along with the non-condensible gases.

Using option 3 is the next cheapest way to go. It is at least 99.5% propylene, at most 0.5% propane, and ppm amounts of stink oil plus even less ppm of contaminants. Propylene has even closer system properties to that of r-22 than propane. It is the next level up in off-the-shelf products in purity, and is readily available in stores that sell the torches that burn it. Again, running it through a filter-drier on its way in will remove the stink oil and any trace contaminants.

For long-term use, it is highly recommended to pony up and buy refrigerant grade gases.
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