First and foremost, like many things around the shop/homestead, there are dangers with certain activities, and this is no exception. Do your research, and never do anything you don’t feel comfortable doing. We only refill tanks bought new, and have a known history of storage. Refilling random empties adds a margin of risk that outweighs the cost savings in our opinion, and we don’t recommend or advocate doing so. Always observe safe storage practices of any tanks, either new or refilled.
We have learned a lot about propane pressure around our farmhouse, and wanted to point out the pressures involved with an operation like this. Outdoor temp at time of filling was 79F, which puts pressure in the tanks around 125 psi. This is not excessively high in our opinion, and we feel an ample margin of safety while refilling my tanks. It should also be noted that the 1lb tank cannot be filled above the pressure of the parent tank if done properly.
Your mileage may vary… Keep in mind it is a federal crime to transport refilled cylinders; which we don’t do. These are all for fuel hungry appliances around the house. That said, where does one start?
A propane tank adapter is a must have for this project. These come in a variety of flavors, and vary in price from $10-$50 depending on how fancy they get. Our model is a Harbor Freight variety, and has performed well over the years.
The only portable tank we have around right now is a 40# tank, that holds 9.2 gallons filled. This tank ran the homestead with many refills prior to installation of our 500 gallon tank. A little awkward to use when full, but it is what we have to work with.
Adapter is installed via the female POL tank connection, and like most flammable gas/vapor applications, is a reverse thread. This means it tightens counter-clockwise, and loosens clockwise.
Filling the 1lb tanks requires the filling tank to be inverted, to allow liquid into the tank instead of vapor. This can be a bit tricky, but it likely the most hazardous part of the operation. It should go without saying, but we will reiterate: this should always be done completely outdoors while using gloves and safety glasses.
Two new cylinders were bought from the local big box store for a recent trip requiring our camp stove. I don’t know the empty weight, but this brand new cylinder has a filled weight of 1 pound, 8.6 ounces as a baseline.
Our empty tank being tared for filling, weighing in at 13 ounces.
As we mentioned prior, you are only using the pressure in the parent tank to fill the 1lb tank. One way to help get more liquid into the 1lb is to freeze it prior to filling. The theory is that the liquid will drop in temperature, thus reducing the vapor pressure and allowing more liquid to flow than at room temperature. There are many folks online who have many opinions on this front, but this is the method we are using for this post.
1lb tank threaded to adapter, tank valve is in the off position. Once the tank is tipped upright, the main valve is cracked open until the flow stops. It is fairly audible, and you will know when it has equalized. Turn the main valve off, and right the container to safely remove the filled cylinder.
Our baseline tank filled with 11.5 ounces of propane, and is within 0.6 ounces of a brand new tank fill. This is indicating that we are not overfilled. Overall, this is a great way to get a few more uses out of these tanks before disposal. These tanks aren’t meant to be pressure cycled indefinitely, and it would help to use a sharpie to mark how many times they have been filled. Refillable tanks are available as well, and are a great investment for those needing DOT approved refillable tanks for transportation.
To end, use your head and always follow manufacturers instructions and warnings. Never fill an unknown tank or one with dents, rust, or any other visual defects. Do not keep or store them inside your home, garage, or vehicle. If or when in doubt, dispose of empties according to local ordinances.