Do you always purge?

[Emperor Zurg]

So, the freezer temps get the remaining fuel and air to 'condense' a bit, allowing more room-temp butane to inject?

There's no air in there. There is butane in there; liquid butane on the bottom and butane vapor above it. Lowering the temperature reduces the vapor pressure of the butane. The result is that the butane CAN, which is at room temperature, is at a higher internal pressure than that of the lighter. That means that fuel will flow from the can into the lighter - which is what you want. The fuel entering the lighter will be chilled by coming into contact with the cold fuel tank so the lighter will remain at lower pressure even as it is being filled.

The worst case scenario is probably what all you people have been doing. That would be taking the lighter out of your warm pocket and attempting to fill it with a room temp can of butane. In that case, even if the lighter is basically empty, the instant a little butane enters the tank, it immediately flashes off on the warm surface of the tank and suddenly the lighter is at equal or higher pressure than the can. So fuel transfer stops with a drop or two of butane in the tank. Then you wonder why you can only get a light or two out of it before it's empty. It MUST be because it's full of AIR because I forgot to purge it! No, it's simply empty because you never got any fuel in it in the first place.

[Deke]

There's no air in there. There is butane in there; liquid butane on the bottom and butane vapor above it. Lowering the temperature reduces the vapor pressure of the butane. The result is that the butane CAN, which is at room temperature is at a higher internal pressure than that of the lighter. That means that fuel will flow from the can into the lighter - which is what you want. The fuel entering the lighter will be chilled by coming into contact with the cold fuel tank so the lighter will remain at lower pressure even as it is being filled.

The worst case scenario is probably what all you people have been doing. That would be taking the lighter out of your warm pocket and attempting to fill it with a room temp can of butane. In that case, even if the lighter is basically empty, the instant a little butane enters the tank, it immediately flashes off on the warm surface of the tank and suddenly the lighter is at equal or higher pressure than the can. So fuel transfer stops with a drop or two of butane in the tank. Then you wonder why you can only get a light or two out of it before it's empty. It MUST be because it's full of AIR because I forgot to purge it! No, it's simply empty because you never got any fuel in it in the first place.

This is spot on. My tailgating grill uses the 1 lb propane cylinders. There is a method of refilling them from a large propane tank through a hose by first putting the one pounder in the freezer. Because of the temperature difference, it makes the propane flow into the smaller tank and end up under pressure.

Same concept here.

[fiddlegrin]

..............The fuel entering the lighter will be chilled by coming into contact with the cold fuel tank so the lighter will remain at lower pressure even as it is being filled. ............

Right on_! Great post.