|A very dangerous canister refiller. ** AVOID! **|
|A "bulk" type 100% propane tank|
What could go wrong? A whole lot, and it could be bad, very bad. First, backpacking canisters do NOT contain 100% propane. Standard backpacking type canisters in the US are rated at not more than 20% propane (mixed with 80% isobutane) or 30% propane (mixed with 70% butane). Propane is a very high pressure gas. Put 100% propane in a canister rated for only 20 to 30 percent propane and what do you get? Quite possibly a very nasty explosion.
Oh! I know! If my canister is only rated for 20 to 30% propane, I'll just fill it up to 20% of capacity and leave the rest empty! Duh! Problem solved.
Uh, not exactly. When combined with butane or isobutane, propane actually forms a blend. The resultant blend has a lower vapor pressure than 100% propane. Odd as it sounds, you'll actually have less vapor pressure in a canister with 20% propane and 80% isobutane than a canister 20% full with propane alone. Besides, what good is a canister you can only fill to 20% of capacity anyway?
Basically, you should never fill a backpacking type canister with 100% propane.
But what if you filled a canister to 80% of capacity with butane first? If you filled to 80% of capacity with butane first and were exactingly careful about not exceeding the overall rated capacity, then maybe this adapter would be safe. I'm not saying that it is safe, I'm saying that there's the possibility that the adapter might be safe -- from the perspective of the mix of gasses. The adapter might still have other problems in terms of materials, design, and construction. The very fact that someone put a dangerous refiller like this together suggests that they really don't know about gasses. I have NO confidence that such a person has the ability to build a refiller that is safe in other respects. I'm certainly not tempted to buy one.
Putting it into perspective
Now, am I just a "Nervous Nellie?" Maybe this is actually pretty safe, but you know this is modern society, and we have to protect people from themselves, don't we?
I submit to you that I am no Nervous Nellie. I refill my backpacking canisters all the time (with butane!!). I use a windscreen with my upright canister gas stove. I sometimes use my stove inside a tent. In other words, I do all sorts of things that manufacturers tell us not to do lest doom and disaster overtake us. I do things like refill, use a windscreen, and cook inside my tent because I've studied the objective dangers and found them reasonable for a person who is careful and has an understanding of how to mitigate the dangers. But I will NEVER fill a standard backpacking type canister with 100% propane. It's just too dangerous. Period.
This refill adapter is: NOT recommended (in the strongest possible terms).
I thank you for joining me on another Adventure In Stoving.