Filling empty propane cylinder from another full cylinder

[skyflyer]

FWIW I have extensive (although not necessarily entirely relevant) experience of refilling cylinders in this way as I used to do a lot of hot-air ballooning. The balloon tanks are aluminium and if you didn't have access to a bulk cylinder you had to decant from "104s', otherwise 47kg cylinders (=104lbs!)

The balloon cylinders were modified aluminium forklift truck cylinders and were fitted with a dip-tube and pressure relief valve. During filling this valve was opened to vent pressure from the aluminium tank which increased the speed of refilling. Once the tank level reached the bottom of the dip tube, liquid started to spurt out and the main valves were shut off. If you delayed it was very easy to get cold-burn off the evaporating liquid from the vent tube!

This left a safe space for expansion if the cylinder warmed up. This was a vital safety measure as the aluminium tanks could and have easily over pressured and burst if there was no expansion space, when heated, even though they had pressure relief valves, in a fire the gas cannot vent quick enough to prevent pressure building up and an explosion (The aforementioned BLEVE)

The disadvantage of a vent tube is that it vents gas! Refuelling fires were not uncommon, caused by some idiot with a lighted cigarette or a static spark!

So with no vent tube the only safe way to do it is by weight. My understanding is that in the USA they dont do exchangeable cylinders like Calor and camping Gaz, but boat owners have a dedicated cylinder on the boat they they get refilled. (and inspected on a schedule) The rule is that it must not be filled more than 42% apparently. I stand to be corrected!

There are further problems with decanting liquid from one cylinder to another. As the filling cylinder empties the gas inside expands and that takes heat from the air and so it cools (ever seen the frosting on the slide of a cylinder that is being rapidly used?). The cooling reduces the pressure so that sometimes no more liquid gas will flow to the 'empty' cylinder, even with the aid of gravity. This is even more likely if there is no vent valve to relieve the pressure in the recipient cylinder, which would be the case on 'boat' cylinders. The solution is to chuck buckets of hot water over the donor cylinder to increase pressure.

The next issue is liquid trapped in the connecting hose. Once refuelling is complete, the tanks should be stood upright and the valves opened to let any liquid in the hose to vaporise back into the cylinders. Then close the valves and only then, disconnect the hose.

If you do this whilst the cylinders are still inverted (i.e. close the valves then disconnect the hose) the hose will be full of liquid gas, which will evaporate and spray out, causing cold burns, fire risk and a lot more volume of gas, once expanded, than a simple hose's worth!.

Of course the steel tanks we use are much more robust than aluminium and are over engineered but bear in mind that the constant "exchange" of empty for new means they are regularly inspected when refilled at the factory, for dents and defects. Before each fill, IIRC. If you are forever re-filling your single cylinder, then who is checking it and testing it?

Just some food for thought.

 

[VicMallows]

A sensible and realistic summary .... even if I can already hear the howls coming from the 'don't even think about it' brigade.

 

[harrym1byt]

It would be extremely useful for me, to be able to decant from one BP/Macgas Gas Light cylinder to another. These are the all plastic bottles, green top, with a see through main lower part, where you can see the level of the liquid inside. I was all set to buy a second 27mm clip on adaptor (no regulator) and have a go at decanting, using my existing adaptor plus an HP hose - when I realised that the 27mm clip-on's include a one way valve. They let gas (or I assume liquid) to flow out of the bottle, but not in.

Is there a source for 27mm clip-on adaptors x W20/M20 which doesn't have a one-way valve please?

 

[jdc]

The one-way valve is trivial to remove (and I never put mine back). I too have a BP / Gaslight / Homebase composite cylinder, first bought in Norway, and find it excellent.

To get the one-way valve out, assuming it's the same as mine (GasBoat), carefully unscrew the outlet M20 connector (iirc it is a left hand thread) and the little piston and spring fall out. Then screw the M20 connector back in. Job done. It was only by doing this that I was able to get the bottle refilled in Brazil where I had to provide the adapter, and since then I've doen it several times by myself.

 

[harrym1byt]

Thanks very much jdc, I will certainly give that a try.

I too find the Gaslight system excellent.

 

[William_H]

I havn't gone through all the replies however around here if you take your cyclinder to a refilling place. You just stand by and watch. Often hardware store or petrol station and they have a huge cylinder as a source. This is connected by a pipe to your cylinder. The overflow valve is opened allowing gas to escape. The valves on both cylinders are opened and the liquid flows from the source. This continues for a few minutes until when the receiving bottle is full to correct level the gas escapng from the overflow vlave clearly turns to liquid. They just shut all valves and away you go. receiving cylinder gets cold due to gas evaporation.
Now this is obviously always done outside. The operators are presumably trained on what to do. No you never hear of an explosion. Obviously also the source bottle has a pick up tube going to the bottom to pick up liquid.
The gas here is always called LPG I don't know if that is liquid propane or petroleum but I think is the same stuff used for cars on gas. Probably the higher evaporating temp type as I know the balloonists even when it is not frosty morning will take the cylinders inside over night to stop them getting too cold. olewill

 

[DeeGee]

Thanks very much jdc, I will certainly give that a try.

I too find the Gaslight system excellent.

jdc may well be correct, but I had to take the pipe with a non-return valve in it and drill out the valve. IIRR it was quite easy. Anyway, I have now had occasion to do this refilling a few times with nary a hitch, despite all the doom-sayers. I always do it outdoors and am a non-smoker !!

 

[PaulRainbow]

Just to give the elf and safety brigade something else to worry about, i used to fill portable oxygen and acetylene bottles from full sized ones. The oxygen was only at about 3000 psi

 

[sailorman]

Just to give the elf and safety brigade something else to worry about, i used to fill portable oxygen and acetylene bottles from full sized ones. The oxygen was only at about 3000 psi

Similar to the air in my Theoben Rapid

 

[PaulRainbow]

Similar to the air in my Theoben Rapid

Yup, but a bit clumsy for pigeon shooting

 

[SVBewildered]

Yes it is possible.

I started doing this in the 1980s when camping gas bottles were not available in Greece and there was no choice. This was carried out on land as I had a fleet of charter boats with camping gas bottles.

Today I hung a 10Kg Greek Gas bottle above my gas locker on my Cape North 43. I was able to successful transfer 9kg filling one 6Kg bottle and topping up a second. Slow and easy is the answer and make sure all gas is off, not smoking or other actions that could ignite gas while this transfer is underway. Cruising yachtsman with North American bottles face this problem often especially in Europe.

Always take all safety precautions and insure the link between the bottles have the correct end fittings.

Also keep in mind that a machine shop could make an adapter to allow filling of your bottles.

Best regards Richard Naylor - S.V. Bewildered

 

[DeeGee]

Just a little bit of extra info: we now live with a buried cistern of gas, it only gets filled to 85%, the delivery man shrugged his shoulders, explaining that it was for safety reasons. This bears out previous mentions of limiting the fill.

 

[ghostlymoron]

Doesn't this mean you have to weigh the receiving bottle during transfer?

Just a little bit of extra info: we now live with a buried cistern of gas, it only gets filled to 85%, the delivery man shrugged his shoulders, explaining that it was for safety reasons. This bears out previous mentions of limiting the fill.

 

[DeeGee]

I marked all my cylinders with their tare weight and use some old bathroom scales, semi calibrated, to keep an eye on how the weight is going in. The downward pressure exerted by the filling tube is ignored as it is an extra safety margin.

The tare weight is normally, almost unreadably, marked on the cylinders.

 

[Heckler]

I would not even think about doing it!! /forums/images/graemlins/shocked.gif

It would mean transfering the liquid component and not the vapours which is where you usually 'tap off' the fuel.

Where were you thinking of doing the decanting of the fuel, on the quay-side or on board your boat?

The UEA is warm and dry part of the world and static discharge is a huge risk and this would need to be taken into account.

The explosive power of propane and butane is considered to be like a mini-nuke and there would be nothng left of you or your boat if it went wrong /forums/images/graemlins/confused.gif

DON'T DO IT - DONT EVEN THINK ABOUT DOING IT!

Petrol is basically the same product, just slightly "heavier" thats why our American friends call it gas! The carb turns petrol into gas! Nothing intrinsically more dangerous handling "gas" then gas!
As the next poster says, NC describes in detail how to do it, no different than refilling a "gas" tank with petrol as long as suitable precautions are taken!
In Australia I watched as the BIL took an empty bottle to the "gas" station and refilled it. Not difficult and no more dangerous than filling a petrol container.

 

[skyflyer]

There is one extra thing to consider - having made your transfer of liquid propane, and turned off both valves, you now have a transfer hose full of liquid propane. When you undo the hose it will expand and vent liquid that becomes a relatively large amount of gas! (The liquid gas can also cause freeze burns)

The solution is to invert both tanks to a normal upright position then open one tank valve again and allow the liquid in the hose to expand back into the bottle, Close the valve, then disconnect the hose and only a small amount of gas will vent.

Blindingly obvious to many, no doubt, but hopefully useful for others

 

[Daydream believer]

Yes - I am sure it is very dangerous - but was common practice in many villages in Africa. Perhaps because of third world attitudes to life expectancy ?
Ken

Common practice in our village - ST Lawrence Bay, Essex- The chap that did it was a teenager at the time. Now in his 70's

 

[William_H]

Petrol is basically the same product, just slightly "heavier" thats why our American friends call it gas! The carb turns petrol into gas! Nothing intrinsically more dangerous handling "gas" then gas!
As the next poster says, NC describes in detail how to do it, no different than refilling a "gas" tank with petrol as long as suitable precautions are taken!
In Australia I watched as the BIL took an empty bottle to the "gas" station and refilled it. Not difficult and no more dangerous than filling a petrol container.

I have seen it done again in Oz so can't be sure gas types are same as UK. (No concern re evaporating/operating at low temps.)
The supplier's tank is quite large and previously filled from a tanker. The supply tank has a dip tube so no need to invert. It is connected to the cylinder to be filled. The little valve on the top of the cylinder is opened with a spanner which lets gas escape. The main valves are opened and liquid gas flows in. When the gas escaping from the tell tale vent turns to liquid as it does when cylinder if full it is obvious as a vapour. Turn off all valves and tell tale valve. The filler hose I think has a valve at the end so hose remains filled with gas. Now obviously with this little valve venting gas while filling you want to be outside and certainly no smoking.
It does seem now that it is more difficult to find someone to fill a cylinder. They tend to prefer the exchange system for largish cylinders as used on a caravan or barbecue. Probably all different in UK. olewill

 

[skyflyer]

I think one of the reasons we have the exchange system is that the cylinders are automatically reinspected.
In the US I believe the owner of a refillable cylinder has to have it inspected and certified at his own cost each year. No certificate means the supplier won’t fill it

 

[Steve_N]

There is one extra thing to consider - having made your transfer of liquid propane, and turned off both valves, you now have a transfer hose full of liquid propane. When you undo the hose it will expand and vent liquid that becomes a relatively large amount of gas! (The liquid gas can also cause freeze burns)

The solution is to invert both tanks to a normal upright position then open one tank valve again and allow the liquid in the hose to expand back into the bottle, Close the valve, then disconnect the hose and only a small amount of gas will vent.

Blindingly obvious to many, no doubt, but hopefully useful for others

I just turn off the top/donor bottle then wait half an hour before closing the valve on the lower/receiving bottle. All the liquid propane has drained out of the hose into the lower bottle by then and only a snift of gas escapes when disconnecting.