Hey, gas canisters are expensive. Why NOT just refill them with cheap gas from a bulk propane tank?


                                A "bulk" propane tank

Yeah, and on eBay you can get a cheap canister refiller that will do just that.


                                A very dangerous canister refill adapter

But refilling backpacking canisters with this particular canister refiller is downright dangerous.
                                   
Find out the whys and wherefores in my latest post: Canister Refiller -- WARNING

HJ
Adventures In Stoving

Edited by hikin_jim on 03/27/2012 14:31:29 MDT.

I don't know if the seller on eBay knows how dangerous his product is. I wrote him but got no answer. I also reported the item to eBay. The item is still there this morning. I really hope no one gets hurt because of this thing. It's not instant death, but it is an accident waiting to happen.

HJ
Adventures In Stoving

If you follow the sellers directions why would it be dangerous? His photos are very descriptive.

Because Jim's science is correct and your could hurt yourself and others. The pressures are easily double what the can is designed for.

I can imagine what Chinese consumer protection regulations are like. I think this character has taken two devices and re-purposed them to work together in a way they were never intentioned. Getting horribly burned or killed to save a couple dollars is just getting in line for the Darwin Award.

Used to work in the aerosol industry. There are DOT specs to the canisters that are used, and can be transported. Any can with the rolled lip and standard aerosol valve, which is what you find on the gas blends canisters, is NOT rated for the pressures propane exerts. That is why the 100% propane canisters are thicker stronger steel, with more robust valves and safety release valves. It is all about the vapor pressure. And to the poster that said that propane and butane are not that different in size, you are right, there is only one -CH2- unit difference, but in a molecule that small, that is a huge percent increase in moelcular weight (propane MW= 44, butane = 58, 31% increase in MW), thus the large drop in vapor pressure from propane to butane.
Another hazard of this is over-filling. All liquified gas canisters should have "head space" to allow for expansion of the gas if it is heated. The hazard being, if you overfill the canister, there is no room for the gas to form, you get hydrostatic pressurization and the canister fails. It is industry standard to leave 15-20% volume of a canister empty for headspace.
I would also say that this device looks incredibly dangerous from the perspecive that the tubing used looks like simple PVC or tygon tubing, which IS NOT RATED for the pressures you are going to be transferring that gas at. You should only be using tubing rated for pressure, which will have a braided stainless sheath around the tubing core.
Another issue to consider as well, the DOT specs for canisters that are considered refillable vs non-refillable. Non-refillabel canisters do not have to pass results for long term use and are not spec'd to be corrosion resistant. When refilling a canister you are potentially introducing water vapor which can potentially corrode the can causing catastrophic failure. Refillable DOT canisters are made with this corrosion resistance in mind, and therefore are "over-built" to make sure that they can withstand some corrosion without failure, at least until the next testing period. ALL refillable DOT canisters have notices on them regarding occasional hydrostatic testing.

Roger said this:

Obviously filling can be done - after all the supplier fills the canister in the first place.

Tony identified one of the major problems. If you overfill a canister and it gets hot it can explode. There MUST be gas space left above the liquid. But without an LPG valve on the canister, how will you know when it is full enough? Dangerous stuff.

There is a second problem. When new the surface of the Lindal valve is nice and smooth and shiny and it seals well agianst the Neoprene or Viton O-ring in the stove. When the canister comes from the factory this plating is protected by the plastic cap. But in our fine profit-driven society we find that the plating on the steel is so **%%$$## thin the steel does start to rust rather quickly. A rusty surface may not seal adequately, leading to a gas leak ...

The canisters are rated to take up to a 30% propane content (depending on brand) at up to 50 C. Fill them with LPG and you have a potential bomb. Trust me, they can explode with appalling consequences. No, don't trust me - go read our article on exploding canisters at
http://www.backpackinglight.com/cgi-bin/backpackinglight/exploding_gas_canisters_the_hazard_of_overheating.html

So, what can you do with the empties? RECYCLE them!
But first make very sure they have been punctured. You don't need to spike the metal - a dangerous business anyhow most of the time. Let the canister run out while using it. Then take it home and hammer a nail down through the Lindal Valve. You will break the plastic doodad inside and all will be well. This can be done with the shepherds hook part of a titanium tent stake too, with skill.

Cheers

Very interesting article to be sure. But given the risks involved... and especially how inexpensive new canisters are... it's really not worth refilling at home. I certainly wouldn't do it.

clear plastic tubing for a pressurized application, i'll take 3!

That's the most dangerous propane hose combo I have seen. First the hose and fitting are made for low pressure air for aquariums Instead of braided rubber hose crimped on so the hose does not come off or leak.

For the size canister we use the canister cost is cheap. I have seen people refill car camping stoves canisters but that dangerous also. Most people just use the refillable large white canister with proper adapter to cook with car camping.
Terry

Roger says canisters are rated to contain 30 percent propane.

Ebay seller says:

"Please observe the change of real-time weight, when the weight reach the rated weight(Suggest below the rated weight, This would ensure security), please close the valve on the big gas tank at once, then close the valve on the Inflatable converter."

The seller clearly suggests to fill below rated weight.

30 percent leaves plenty of head room for expansion.

Using an electronic scale as instructed by seller will let us know when to close main valve. The electronic scale is our safety gauge.

Fill to recommended weight and were good to go.

Use appropriate hose and clamps and were good to go.

potentially missing the point, but 30% full of 100% propane is still 100% propane and all the vapor pressure that come with it.

I don't see how under filling addresses that the canisters are not built to hold the pressure.

The hose is the safety as it was pop before the can ;)

That's the most dangerous propane hose combo I have seen. First the hose and fitting are made for low pressure air for aquariums

As soon as you have liquid propane in the canister the canister pressure will be the vapour pressure of the fluid.

So it doesn't matter if the canister is 90% filled with liquid and 10% filled with gas or 10% filled with liquid and 90% filled with gas the Vapour pressure and therefore the pressure the canister sees is the same.

Therefore a canister not designed for 100% propane vapour pressure is not safe to fill to any capacity with propane.

Roger says canisters are rated to contain 30 percent propane.

And in another thread Roger said this:

"A caution about what you use for refilling. While the standard canisters are rated for 70%(iso)butane/ 30%propane, they are NOT rated for straight propane. Propane has a far lower boiling point and will make the pressure too high for the ratings."

And in the same thread Edvin said this:

edvin mellergård
(Edvin)

Real scientific figures on 07/18/2010 13:05:28 MDT
At the end on this page there is a graph displaying the pressure for variuos propane and butane blends, both in metric and imperial.

http://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html

Dan,

The tables from the engineering tool box site you reference prove why this device is not safe.

At 60F a 100% propane mixture, regardless of how much you put in the container will have a pressure of 93 psi

At 60F a 70% Butane, 30% propane mis, regardless of how full the canister is will have pressure of 36psi.

The canisters have been designed for the Butane/propane mix and not just pure propane. By filling with pure propane you are over doubling the pressure in the container. This is not safe.

What part of the Eng tool box table makes you think that this is safe to do?

Hi, Dan,

Yes! You've got it. This is exactly what I've been trying to get across and why I'm so concerned about this particular refiller.

If someone uses this particular refiller, they can wind up with pressures inside the canister that are WAY over what the canister is designed for.

This is a good discussion. Thanks for asking the questions.

HJ
Adventures In Stoving

Kudos to Hikin Jim for hiliting this and keeping on it. Folks need to be informed.

The behavior of mixtures vis-a-vis vapor pressure does seem counter intuitive but that does not make it false! I can only point out that it is not reasonable to deny or fail to accept advice that this is dangerous when the only reason is that you don't understand why. You need to have a reason to believe or accept that it IS safe.

Sorry to be blunt, but proceeding in absence of that reason is volunteering for what one local radio personality used to call "Nature weeding out the stupid".

OK, I'll crawl back under my rock now.

My Snow Peak canisters read, "WARNING: DO NOT REFILL."

My 1 lb propane canisters read, "Never refill this cylinder. Refilling may cause explosion. Federal law forbids transportation if refilled - penalty up to $500,000 and 5 years imprisonment (49 U.S.C. 5124).

I knew this before Jim posted the thread. I am sure my MSR canisters have similar warnings, but I am too lazy to walk out to the garage and get one.

Why warn people, let nature (Darwin) takes its course. Fewer people in the wilderness the way I look at it. :)