I watched several youtubes about filling the small (1 lb) tanks off the
20 pound tanks. In all of them they mention purging out the air. Where does this air come from ?Is it because the small tanks are ran all the way empty and the air then gets in ?
troposphere
Bingo!
Where does it get in? Valve closes when you take the torch off.
Hey, a 1 lb propane cylinder might make a nice portable compressed air tank.
I don't think you want to flic your bic near that 'air'.
I suspect it isn’t air but propane gas.
The refill process tends to transfer liquid propane, the donor cylinder being inverted so the liquid is transferred. The cylinder being filled gradually builds up pressure and the flow stops. Releasing some gas allows more liquid to flow in.
Of course the process isn’t exactly without risk to put it mildly and at least in the UK the companies who technically own the cylinders have rules against it. There are cylinders designed to be refilled of course which have safety features built in.
What isn’t clear is how the cylinders designed to be refilled (in particular the large ones designed for motorhomes caravans etc) avoid the need to be vented. It could be as simple as the pumps at filling stations simply run at a high enough pressure to overcome the the problem.
+1
I agree with Brian, it's the propane in the gas phase that they want to get out so it can be replaced with liquid propane. The only way for air to get inside would be to have an appliance of some kind connected and leave the valve open. And then you'd have to do it for a long time for any significant amount of air to interchange and get inside the tank.
That is what I was thinking. It was not just one,but several of the youtube videos that mentioned air and not propane gas. Looks to me that evenif you do vent the propane gas, just as soon as you do more will boil off the liquid in the samll tank and you would be right back where you started from.
I am beginning to think those doing the venting of the small tanks are just blowing smoke and do not know what they are talking about.
I have never tried filling the small tanks as I have never lost power for very long. I do have a camping stove and 2 propane lanterns that use the small bottles. I have about a dozen small bottles put back. I bought a propane/gas dual fuel generator a few months back. As I bought some 20 pound tanks for it, I thought I may use them to fill a small tamnk some day. I did just order the refill adaptor. Then the research on youtube seemed to lead me down the wrong path. I have seen some things on youtube that I know are very wrong, so I questioned the refilling when air was mentioned. Then even if the propne gas is let out, I would think that in the short time it takes to screw the bottle back on the large tank it would build up the pressure again.
My only experance with propane filling was at work where the forklifts ran on propane. We had a big tank to fill the 30 or so pound tanks on the forklifts. It had a pump that did the actual transfer. As I was not a forklift driver, but did need to use one from time to time, I was taugh how to do the filling. Only did it about 2 times and that was about 10 years ago. I don't know how much was put in the tanks as I really did not care because I was only going to use the forklift for about half an hour. I just did not want to run empty.
I just bought a campstove hose that connects the campstove or lantern or whatever directly to the 20 lb cyl. There is even a "manifold" available to connect multiple devices at once. Why fool around with 1 lb cyls that often leak when you remove them anyway?????
You are probably right about that in many cases. I just ordered one of those off ebay for less than $ 10. That is about the same as the refill adaptor.
Why have you crossposted your message to a Vietnam group? Do Vietnam Vets miss blowing stuff up so much they need another way to do it? Your post sounds like a great way to live dangerously. Note I removed that group. Brian
The large cylinders (eg for motorhomes/caravans) in the UK designed to refilled have special valves which limit how much you can fill them- typically 80% of their max capacity. The none refillable ones lack this feature.
The above cylinders are also designed for vapour take off, the liquid sits at the bottom of the tank and there is a ‘hulling’ area above filled with vapour which the outlet is taken from.
There are also tanks designed for liquid take off, used in things like fork lifts. I assume they are simply operated so the liquid is by the outlet ie upside down or similar.
Equipment designed for vapour take off becomes very dangerous if fed with liquid LPG.
I believe that, in the US, you take your cylinder and it is refilled. In the UK, and most of Europe AFAIK, you exchange your empty cylinder for a full one. The cylinder remain the property of the gas company, at least technically. In practice, people discard them when no longer needed etc.
Back when we were racing and using 20# nitrous cylinders we would fill them from the big ones just by putting the small one in a vat of ice water and hooking it up to the big one sitting in the sun. The difference in temperature would distill that liquid right into the little cylinder The fear was more of over filling them than not getting enough it. A good scale is your friend here. Vent off the excess into an empty one until you get the weight right.
Yeah, makes sense at home, not so much hiking the Appalachian Trail.
In the US you usually buy the small 20 to 100 lb tanks. You then take them to a place that fills them,if the place you buy them does not have a filling tank. You can also go to some stores that will exchange your small tank that is empty for one that is full. Lots of grocery stores seem to have the exchange tanks. They do not fill them, but the company I have seen in this area is called Blue Rhino takes the tanks off, cleans them up and puts propane in them and takes them to whever they are needed to restock.
The tanks were changed a number of years ago so you could not put more than 80% in them. I have heard that some of the exchange places put less than that in the tanks. Just a way of fooling the public for more profit. You just have to read the fine print.
The filling of the smaller 1 pound type cans do show people using a scale. You weigh the empty tank and then weigh it after you put some propane in it. Many years ago I took a 20 pound tank to a place and the weighed it before and after filling. That was before the 80% fill limit valve.
I just hada 20 lbb tank filled and it was about $ 12. That means I can fill the 1 lb tanks for about $ 1.50.
It was mentioned about just using a hose to use the 20 lb or larger tanks. This is fine at home, but going camping or some other activities you may not want to dran along a big tank. A friend has a small ( about 500 to 700 watt) generator that runs on the small 1 lb tank. Not sure what he uses it for,but I have one that is gas powered that I often use around the yard to power various electric tools that is out of reach of my 100 ft drop cord from the house.
That's where you use a naptha backpacking stove like a whisperlite or a dragonfly or a Trangia alcohol stove. The dragonfly even runs on Kero if you don't like carrying white gas, and weighs under a lb.
Yup, or exchange for a full one. Many filling stations here in UK stock them of different sizes.
But cars that run on propane are a different matter.
Personally, I wouldn't bother.
Tone
Blur Rhino puts 15 pounds in theirs. So it is nominally a 20 pound tank, they limit it 18 and BR sells you 15.
I don't know how many through hikers carry 1 lb canisters. I used to carry a Svea 123 but lately I've been using a Mini Trangia alcohol stove. It's lighter and quiet, compared to cooking on a blowtorch. I do use the 1# canisters in AZ. My 20 pounders are old without the mandated shutoffs so for a couple of weeks it's more economical.
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