Need to refill small gas cylinders?

[corvus]

I have only ever refilled canisters from an known provenance,450 g Isobutane to 230g cans (empty they weigh around 131g) check the weight to less than 365g and for summer use 220g cheap Butane to 230g so no danger of overfill there.
That "exploding" cannister I suspect would have been subjected to very high temperatures on the back shelf of a parked car

[hikin_jim]

It doesn't take that much force on a very small area (ie, a burst cannister's wall being forced out at high speed) to cause tempered glass to shatter.

Ah. I've experienced that myself. Good point. Still not sure I'd want to chance it, but good point.

HJ

[Orion]

I was really hoping, begging practically, for a photo. Surely somebody has one?

I read on backpackinglight that Roger Caffin intentionally overheated a gas canister until it blew up. He must throw fun parties. His article is behind a paywall but I'd be surprised if it didn't include a photo or two. From posted comments I gather that he used 30% propane and then heated the canister until at just below 100°C the bottom blew clean off.

[hikin_jim]

Roger's article did include some photos as I recall, but the bottom of the canister everted and separated from the canister. I'm not sure that it's comparable to a canister that did not burst.

HJ

[icefest]

Roger Caffin has done a destructive test on gas canisters. He filled them with a nonflammable gas then heated them in a water bath outside. His canister did not bulge before explosive decompression. The base seam just gave way.
Unless you have done good calibration weights I'd suggest underfilling by 5%. I have know scale that displayed weights up to tenths of a gram to be out by 10 grams, which is too much on a 100g canister.

[Moondog55]

My scales are calibrated [ that's SOP for cooks] so I don't think I overfilled, and none of the other canisters look anything except perfect.

[Orion]

Roger Caffin has done a destructive test on gas canisters. He filled them with a nonflammable gas then heated them in a water bath outside.

What nonflammable gas did he use? I thought that he posted that he used 33g of of a 30% propane 70% isobutane mixture here. I was wondering how he avoided a fireball. And also if there is a slow motion video.

Unless you have done good calibration weights I'd suggest underfilling by 5%. I have know scale that displayed weights up to tenths of a gram to be out by 10 grams, which is too much on a 100g canister.

How did you come up with 10g being too much? I think there's more free play than that.

[icefest]

Orion, my subscription has lapsed and I apologize for my poor memory, that's the article I was referring to. If I recall Boyle's law correctly, 10g overfill on a 100g canister would be the equivalent of a 10% increase in absolute temperature. 0°c be the pressure of 27°c. That would mean that you reach the normal pressure of 50°c at roughly body temperature in your overfilled canister. There is no way I would be happy to use that. Please correct me if I'm wrong.

[hikin_jim]

you reach the normal pressure of 50°c at roughly body temperature in your overfilled canister.

Yipes!

I've been very conservative in my refilling, using only 100% n-butane in canisters that originally came in propane-isobutane mixes. An 80/20 isobutane/propane mix will have a significantly higher pressure than 100% n-butane. People have encouraged me to refill with some amount of propane, but I have steadfastly declined to do so for that reason. Overfill with propane, and you might be ascending a good deal higher than planned if you get my meaning.

HJ

[Orion]

I don't have a BPL subscription and never read the article. I just read what Roger posted in the public "companion" thread.

As for the amount of overfill, it has nothing to do with Boyle's Law.

First, note that a Jetboil 100g canister appears to have identical dimensions as a Snowpeak 110g canister. That right there suggests that Moondog could have gone over by 10g without any worry.

I think the problem with overfilling is two-fold. First, an overfilled canister may emit liquid fuel into the stove causing a flare-up. Second, if the canister is filled with liquid and then heated the liquid can expand beyond the volume of the canister resulting in bulging or rupture.

I measured an empty Jetboil 100 canister and it was a little over 240ml. The amount of 20/80 fuel needed to fill that volume is 130g at 30°C or 124g at 50°C. So it's more like 20-30g over the 100g level that Moondog measured. He'd have to have a seriously screwed up scale to be that far off.

[Strider]

110g vs 100g might have something to do with the different gas mixtures?

[Orion]

110g vs 100g might have something to do with the different gas mixtures?

I don't think so. Snowpeak is supposed to be 15/85% propane/isobutane and Jetboil 20/80%. The difference in densities of these two mixtures is negligible. Besides, MSR is supposedly 20/80 just like Jetboil and it comes in a seemingly identically shaped canister.

[icefest]

I'm with Jim on this one, only use n-butane and be very careful with overfill. I'm not going to guess about relative safety margins.

Merry Christmas.

[Orion]

I wouldn't guess either. I'd figure it out if I were going to refill canisters. But in lieu of that knowledge I agree with you and Jim that the conservative approach is wise. That's why I don't refill at all.

What I would like to do is blow up a canister like Roger did. That sounds like fun.

[icefest]

You could probably do it quite easily in the same way dive bottles are pressure tested.

Fill it up 95% with water, then immerse it under 1m of water and slowly inflate it using another gas, preferably nonflammable.

If you stand back 20m and do it in 5psi increments it should be relatively safe.

[Orion]

I thought about simply pumping it up with air. But it would be way more fun to heat a canister that has fuel in it, like Roger said he did in that companion thread. Here's one of his posts:

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Exploding Gas Canisters: The Hazard of Overheating on 05/03/2007 15:22:03 MDT

Hi Tom

> what influence has the amount of fuel inside the canister on the temperature at which the bottom of the canister pops out? You used 33 grams of the gasmixture

Yeah, this bit gets technical.

If there is liquid fuel in the canister, the pressure of the vapour is set by the laws of physics - the so-called 'vapour pressure'. The vapour pressure of the liquid is set by the temperature, as shown by the graph in the article. The key thing here is that it does NOT matter how much liquid is in the canister, just that there still is some liquid. I know some people have written otherwise, but they are wrong.

Of course, once your canister gets very low you can't be sure what the remaining liquid fuel is: 30% propane, or maybe just 10% propane, so there is some uncertainty about the pressure. Under most any circumstances I can think of, the concentration of propane will not be greater than the initial concentration, so the pressure may be a little lower than predicted.

In the case of the experiments described, the liquid in the canister would have been very close to 30% propane and 70 % isobutane, because I refilled some empty canisters from a new canister of known mix. However, refilling canisters is complex and something I strongly recommend you do NOT try. I only did it for this article; I do NOT do it for normal use.

If the amount of fuel in the canister is small, such that it all turns to vapour as it heats up, then the pressure will be different - lower in fact. Then and only then does the PV=nKT equation come into play.

Hope this helps.
Cheers

[hikin_jim]

110g vs 100g might have something to do with the different gas mixtures?

I don't think so. Snowpeak is supposed to be 15/85% propane/isobutane and Jetboil 20/80%. The difference in densities of these two mixtures is negligible. Besides, MSR is supposedly 20/80 just like Jetboil and it comes in a seemingly identically shaped canister.

My understanding is that most of the major brands are all made in the same factory in Korea. MSR, Primus, Optimus, Jetboil, and Snow Peak are all labeled as "made in Korea", and all have the same molding markings on the caps.

HJ

[Moondog55]

HJ That has been my understanding as well, most of the worlds supply of canister gas for bushwalking and climbing comes from a single factory in Korea

[Orion]

My understanding is that most of the major brands are all made in the same factory in Korea. MSR, Primus, Optimus, Jetboil, and Snow Peak are all labeled as "made in Korea", and all have the same molding markings on the caps.

We're not talking about the caps. Are all the metal canisters from the brands you listed identical? Not according to their web sites. But in the cases I mentioned above they appear to be the same or very nearly the same in shape and size.

[hikin_jim]

The contents of the canisters differ brand to brand. The canisters themselves appear to all be the same. Maybe I'll weigh some empties from various brands and see if there are any differences. If the canisters are all coming from the same factory, it would be hard for me to imagine that they'd make a 110g canister for say Jetboil differently from a canister for say MSR.

HJ

[aronwidforss]

I'm not from Australia and have therefore never seen the need to post before. But i thougth you could find these images interesting.

http://www.utsidan.se/forum/showpost.php?p=505210&postcount=45

They were supplied by Primus AB in a Swedish discussion where the question of refilling of propane blends came up. Apparently the owner of the Omnifuel had refilled the bottles and had them placed on the lid of the ETApot. Those of you who own one of these pots know that the lid doesn't easily go above 50 degrees C.

The bottle exploded and pushed the pot down over the stove. Apparently the stove is still working though.

[Orion]

The contents of the canisters differ brand to brand. The canisters themselves appear to all be the same. Maybe I'll weigh some empties from various brands and see if there are any differences. If the canisters are all coming from the same factory, it would be hard for me to imagine that they'd make a 110g canister for say Jetboil differently from a canister for say MSR.

It isn't that hard to imagine, is it?

Look at a recent vintage MSR 227g canister. They print the gross weight on the outside. Now look up the specs on the Jetboil web site for the gross weight of their 230g canister. Even though the Jetboil canister has an extra 3g of fuel its gross weight is about 20g less. That suggests that they aren't identical containers.

The other thing to keep in mind is that they change them over time. The 110g Snowpeak canisters used to weigh about 10g less empty than they do now. I have some 220g Snowpeak canisters that I bought last year that are clearly a different shape than the 227g MSR canisters I bought at the same time. Do they have the same volume? I wouldn't hazard a guess.

[hikin_jim]

Good questions. I'm away right now and don't have access to my canisters. I'll weigh some empties when I get home from mum's. She's fattening me up with beef and home made pie, so you'll pardon me if I don't drop everything to go weigh some empty metal canisters.

One thing to note is that Snow Peak was the last of the hold outs. Until about 2011/2012 Snow Peak made their canisters were made in Japan. Apparently they decided to outsource production to Korea. The SP canisters are definitely different now.

Made in Japan, left. Made in Korea, right.

HJ

[madmacca]

I'm not from Australia and have therefore never seen the need to post before. But i thougth you could find these images interesting.

http://www.utsidan.se/forum/showpost.php?p=505210&postcount=45

They were supplied by Primus AB in a Swedish discussion where the question of refilling of propane blends came up. Apparently the owner of the Omnifuel had refilled the bottles and had them placed on the lid of the ETApot. Those of you who own one of these pots know that the lid doesn't easily go above 50 degrees C.

The bottle exploded and pushed the pot down over the stove. Apparently the stove is still working though.

Aronwidforss,

Thanks for the link, and the photos. Google translate took care of the text, but those photos need no translation.

My understanding is that the vapor pressure of propane is a lot higher than that of butane, iso-butane, etc. The photos are a graphic illustration of the risks of refilling with a propane-rich blend and exceeding the tolerances of a standard cannister.

[hikin_jim]

The 110g Snowpeak canisters used to weigh about 10g less empty than they do now.

Absolutely. The Snow Peak canisters made in Japan are about 10g lighter than the ones made in Korea.

I weighed 10 or so made in Korea canisters of the 100 to 110 g class yesterday. They all came in with a canister weight of about 100g. There was some variability, from about 98 g to 102 g, but the variability was not correlated to brand. In other words canisters all from the same brand showed minor variations in weight. I weighed MSR, Snow Peak, Jetboil, and Optimus brand canisters, all made in Korea, all with identical dimensions and all with identical caps (except for color). Does that prove they're all made in the same factory? Well, no, not at all, but it is at least consistent with them all being made by the same company if indeed that were the case.

I have some 220g Snowpeak canisters that I bought last year that are clearly a different shape than the 227g MSR canisters I bought at the same time. Do they have the same volume? I wouldn't hazard a guess.

I'd be very curious as to where the canisters were made. The Snow Peak canisters made in Japan are very clearly different from the Snow Peak canisters made in Korea.

I guess this is all somewhat abstruse. For sure I wouldn't refill with a mix with higher vapor pressure than the original, no matter where the canister was made.

HJ

[Moondog55]

I would have said the rupture was due to misuse myself, I read that as having heated the canister to higher than hand hot temperatures.
None of the other 3 canisters I refilled show signs of anything abnormal [ which reminds me i should take it out of the deep freezer and puncture it for recycling

[Orion]

I'd be very curious as to where the canisters were made. The Snow Peak canisters made in Japan are very clearly different from the Snow Peak canisters made in Korea.

It was one from Japan, purchased within the last year from REI.

That still doesn't explain the difference in the Jetboil 230 canisters though. Are they wrong about the gross weight of their canisters or are they different? I hope they are. I rather like the idea of more fuel in a slightly lighter canister.

I guess this is all somewhat abstruse. For sure I wouldn't refill with a mix with higher vapor pressure than the original, no matter where the canister was made.

I thought the whole canister size question was in reference to overfilling, not filling with a more volatile mixture.

That said, if a few precautions were taken it wouldn't be unreasonable to use something more volatile than any of the commercially available blends. The limits are there to protect you against a certain degree of abuse. If you stored the canisters where they stayed relatively cool, didn't leave them in the trunk of your car, used them inverted so they weren't exposed to the stove flame, etc, you could enrich the mixture without worrying about a bomb going off. I'm not suggesting that's worth doing. I don't think refilling is worth doing. But it wouldn't be crazy dangerous if you went about it intelligently.

[hikin_jim]

The real issue, whether overfilling or refilling with a higher pressure mix, is pressure.

With regard to overfilling, I think there's a good safety margin there. I notice that canisters routinely overfill by 2 or 3 grams with no apparent harm.

A lower pressure fuel only adds to that safety margin.

HJ

[Mark F]

My take on the over-fill/over-pressure issue is that as a canister heats up and the internal pressure increases, the liquid component expands and the gas component is compressed with some of the gas converting to liquid. In an over-fill situation the the expansion of the liquid component may fully fill the canister reducing the gas volume to zero. Then the internal pressure increases far faster than when there is sufficient gas volume to absorb the increasing volume of the liquid. If you fully filled a canister at room temperature (20 deg C) it may only need heating to 25 degrees before rupturing where as one with enough gas volume will withstand heating to 40 or 50 degrees.

[Orion]

In an over-fill situation the the expansion of the liquid component may fully fill the canister reducing the gas volume to zero. Then the internal pressure increases far faster than when there is sufficient gas volume to absorb the increasing volume of the liquid. If you fully filled a canister at room temperature (20 deg C) it may only need heating to 25 degrees before rupturing where as one with enough gas volume will withstand heating to 40 or 50 degrees.

It's hard to know when rupturing will occur since the pressure will drop if the canister expands or bulges as the liquid expands. From 20 to 25°C the liquid fuel would expand about 1%. In a 110g canister that would be a few milliliters, just half a spoonful. These canisters are required "to reverse before bursting" so you might expect that you'd be okay, ending up with something like Moondog's canister... at least most of the time.

Modern propane tanks have overfill protection built in. Part of the problem with an overfilled propane tank is that it will eject liquid fuel through an appliance, before there is a risk of tank rupture. The same is probably true of the small backpacking canisters.