UPDATE: check out this more recent post to learn how I assembled my own super-duper propane refill adapter!
It’s my new manifesto, sort of. See, these 16-ounce "disposable" propane cylinders are such a convenient size for camping and cruising on smaller boats, sometimes there isn’t any other alternative. In the lazarette aboard Two Lucky Fish, A C-Dory 22, this is really the only propane storage solution that doesn’t involve a costly custom propane installation.
So go ahead and use the 16-oz cylinders if you can’t fit one of the DOT-approved refillable cylinders. It’s a shame that even major suppliers such as Coleman have no recycling recommendations for them.
But I’ve learned that they CAN be refilled. The reason you don’t hear much about it, though, is that these cylinders aren’t DOT-approved for refilling. This means that you can’t take your cylinders to the local propane-equipped service station and have them refilled. That’s against the law. And refilled cylinders can’t be sold commercially. And commercial operators can’t transport refilled cylinders across state lines. There are all sorts of limitations and potential liabilities associated with refilling these cylinders.
It’s perfectly legal to refill them for personal use, however.
Obviously, because it’s propane, you need to handle it properly and observe all the best-practice safety protocols.
First thing, though, you need to purchase one of these little adapters from Mr. Heater or one of their distributors.
I got mine at Joe’s (which was G.I. Joe’s when I was a kid, and actually sold military surplus gear, but I digress). Cabela’s sells a similar item called the Mac Coupler, and it’s worthwhile to read the negative reviews on their site.
The negative reviews, which are by far the minority, describe some of the difficulties people experience using this adapter. This can be helpful, because there are a few tricks to refilling these cylinders. To obtain the best results, it helps to understand a little bit about how propane works.
At normal atmospheric pressure and temperature, propane is a gas. It’s heavier than air, so it will tend to settle and collect in low spots, such as the bilge, cockpit, or cabin of a boat. That’s what creates the explosion risk when there is a propane leak, and that’s why propane storage locations must be designed to vent overboard, not inboard. This is absolutely crucial. Don’t cut corners here.
The propane we purchase is "Liquefied Propane Gas" (LPG), which has been compressed into a liquid and is stored in cylinders designed to keep the propane compressed. The propane is always under pressure, and will tend to escape if you let it. So the integrity of your storage cylinder is another extremely important safety factor. Don’t skimp. I don’t know what the lifespan of refilled "disposable" cylinders is, but if they leak or they’re visibly damaged, it’s time to get ride of them.
Myth: larger propane cylinders generate more pressure than small tanks. This is false, they all generate the same pressure, which is dependent on temperature. Lower ambient temperatures produce lower internal cylinder pressures. Higher temperatures produce higher pressures. That’s why one of the guidelines for refilling disposable propane cylinders is not to do it in direct sunlight or on hot days; you could be dealing with very high pressures indeed under those circumstances.
See, what happens inside the cylinder is that the liquid gas vaporizes just until the pressure is sufficient to prevent additional vaporization, which depends on the temperature.
Pressure keeps the propane a liquid, right? And the vaporized propane gas exerts pressure, right? So just enough of the liquid vaporizes to maintain the pressure inside the cylinder to prevent any more of the liquid propane from vaporizing. Got it?
Then you come along, open the valve, light your grill, and thereby release some of the pressure inside the cylinder. Propane abhors a vacuum, so the liquid starts vaporizing again to "fill the vacuum" left behind due to your cooking.
So here’s an interesting feature of propane systems: As long as some liquid propane remains in the tank to vaporize, whether it’s 90% full or 10% full, the pressure inside the cylinder remains constant. That’s why you can cook just as well with a nearly-empty tank as with a full tank.
OK, back to the subject at hand: refilling disposable propane cylinders. The goal is to move LIQUID propane into the empty cylinder. It does no good to move GAS into the cylinder. The heavier liquid sits at the bottom of a cylinder, and the lighter gas sits at the top.
So there are two tricks involved in getting liquid out of your big DOT-approved cylinder and into your small one. First, you need to turn the big supply tank upside down, so that the pressure inside the cylinder pushes liquid, not gas, out through the valve.
Second, you need to create a pressure differential between the supply cylinder and the cylinder being refilled. There are two ways to do this: The official way is to chill the empty cylinder. Remember how propane pressure depends on the ambient temperature? If you can keep the supply tank at room temperature and chill the empty cylinder in the fridge for 15 minutes, you can create some temperature differential, and therefore some pressure differential.
But even so, many users report that they only get about a half-full cylinder this way. It may take some experimenting to get it to work optimally. Chill the empties longer? Freeze them? I’m not really sure. Feedback from readers is most welcome on this!
To get a full refill, you could reduce the pressure in the cylinder another way, though. It’s possible, I learned, to take a pair of needle-nose pliers and pull the pin on the pressure relief valve of the cylinder you’re refilling. This reduces the pressure and allows the liquid propane to fill the cylinder.
If the instructions that come with your refill adapter don’t mention this method, though, it’s probably because it entails more potential risk than the manufacturer’s liability attorneys are willing to accept. Obviously, you should not use these refill adapters in any manner that differs from that described in the documentation.
Still, if you were to give it a try, as I did, you might discover that it works so well that you can overfill an empty propane cylinder. I used a postal scale to compare mine to a new, full cylinder, and I got about two ounces more into the cylinder using the pull-the-pin method. So if one were, hypothetically, inclined to use this method, which one should take care NOT do, of course, I would strongly urge one to weigh one’s cylinders to ensure one is not overfilling them.
Regardless of the method you use, though, once you’ve refilled a cylinder, you should place some soapy water on both valves (the pressure relief valve and the regular valve you connect to your appliance) and check for bubbles. Bubbles = leaks. I had some extremely slow leakage from my overfilled cylinder, barely perceptible, coming out the pressure relief valve. I left the cylinder outside overnight where the propane would tend to dissipate and not collect. In the morning, the cylinder weighed about the same as it had the night before, but it was no longer leaking. I assume the relief valve was working as designed.
I cooked with it at home until it weighed the same or less than a new, full container, before taking it to the boat. I cooked aboard the boat last week while the kitchen floor was being refinished at home, and now I’m cooking with this cylinder at home again. It seems to be working just fine.
I’ve intentionally avoided providing a step-by-step procedural description of the refill process. I’ve probably put myself at enough risk here already! The adapters all come with instructions, and you should follow them.
For liability purposes, I should once again advise you NOT to pull the pin on your cylinder’s pressure relief valve. If you do so, you do so at your own risk.
Hopefully, though, I’ve given you enough background to understand how the process works and why the instructions are written the way they are.