Selecting a Canister Stove for Cold Weather BackpackingPart I: Stove and Fuel Fundamentals

[Robert Miller]

I was surprised to see the blue plastic extend so far. The lower exposed portion broke off. Note the gaskets.

[Brian James]

Oooh… so pretty.

I’m wondering if that metal “cap” that seems to form the sealing surface of the valve could be the safety mechanism. If that cap were heated enough, would it expand outwards and seal the valve?

Or am I seeing that right?

[Robert Miller]

I hadn’t cut to the centerline of the lindal valve in the previous pic. Note the two layers of the metal portion. Both are ferrous.

[Robert Miller]

Here is a close to 180 degree section of a lindal valve. From the top down – exposed metal layers, black neoprene gasket, the red plastic plunger seats against the neoprene with pressure from the spring. The blue plastic acts as a guide for the spring and valve.

Side view of the red plunger. The left end would normally be down.

Top view of the red plunger. The circular feature seats on the neoprene gasket. The dowel in the center is depressed when the stove is screwed on releasing the gas.

[cushing hamlen]

Robert – thank you for you excellent job of dissecting the valve, and the great pictures that show us what you see. Once at home (and the kids in bed) I pulled out an (almost empty) MSR cannister…and at least looking at if from the top, your pictures seem to make great sense. Contrary to what might seem to “make sense”….it would not appear that the valves have any safety shutoff mechanism at all. Check me on this: my interpretation of what I see is that the inner blue plastic sleeve acts simply as a retainer/tensioner for the spring, which in turn loads the red valve plunger, which in turn loads the valve gasket against the top of the threaded shaft. Put on the stove burner, the red plunger gets depressed against the spring, the gasket becomes unloaded, and gas gets past the whole thing.

If it gets too hot, the gasket could deform and loose the seal (though the material is probably cross-linked, and would simply burn, not just deform), the red plunger could warp, and again you loose the seal, or the blue sleeve could deform and/or break, in which case the loading from the spring is lost, and you get catastrophic loss of the seal. In the end, once you take the burner head off, you leak out all your remaining fuel (either slow, or really, really fast!).

Does this look correct to you? Do you see anything that looks like it might act as a safety “shut-off?”

If what I said above is correct, then we would need to look at the thermal behavior of the red and blue plastic parts, and also the seal, and see which degrades at the lowest temperatures (for the techno-geeks out there – look the the glass-transition temperatures of the red and blue parts, and the decomposition temp. for the gasket….).

I think I will go let that almost empty MSR can leak out its remaining fuel and liberate those parts. Maybe next week I can get some time on the machine I need and do that thermal testing…..please bear with me though if it takes longer – the next several weeks are either busy, or have me out of town…..

Thanks again Robert – excellent work!

added in edit: oh, by the way, pretty much the highest temperature you can expect plastics to not become soft at is about 200C (though this is really high-end)…but that at least puts one boundary on the quesion.

[Brian James]

Great photos! They are definitely worth a thousand words!

My a-technical interpretation is this: when the red and blue portions get too hot, perhaps they melt and fuse together. Specifically with the (now hot) gases flowing around them, is it possible that the two pieces simply become one gob of molten-hot goo and seal the canister?

Perhaps malleability of any sort cause the blue piece to lose retention of the spring; causing catastrophic seal failure.

Having never owned a canister product, can anyone answer me this? Do canister stoves/lanterns have their own valves, or do they operate by variable depression of the canister’s valve? I think you could find this out by looking at the needle on the bottom of your stove and operating the flame control.

Cushing, I look forward to the results of your investigation!

Brian

[Robert Miller]

I resized some earlier pics. Hit your refresh button to load them.

Cushing,

Your description is accurate and much clearer than mine, thanks. I took the liberty to borrow some of your verbage and edited some of my captions above for clarity.

Here is my theory on how the safety shut off works. Refer to the last picture I posted. –

The dowel in the center of the red plunger is in a hollow recess. This allows the hot butane vapors to swirl around the dowel softening it until it mushrooms under pressure from the spring while the rest of the plunger remains functional and cooler due to its greater relative mass. Once mushroomed the plunger reseats itself against the neoprene gasket cutting the flow of gas. The canister becomes unusable even though it may contain gas. In an earlier post Coin Page confirmed he had experienced this.

The plunger would perform its primary function perfectly if it were a simple blunt end. IMO, the only reason to design in the dowel and recess is as a safety shut off mechanism.

Brian, good question. This valves only function is to contain the gas in the canister, there is a seperate valve which controls the flow of gas to the burner.

[Miguel Arboleda]

I haven’t a clue as to what you guys are talking about, but it just occurred to me how wondrous and strange and delightful it is that people who might be separated by thousands of miles can actually discuss in minute detail the inner workings of a stove valve. Who would have imagined this twenty years ago?

[cushing hamlen]

Robert – there are some dimensional constraints on what can be molded that might dictate the presence of the dowel in the middle of the red piece….but that said, your thoughts on deformation of the dowel make a great deal of sense…especially with that nice, small, probe from the burner head pushing on it (read – small = higher local pressure from the probe onto the dowel = first location to deform when the red piece gets too hot). I do not recall who posted the comment, but well thought out designs DO typically need to assume they need to be “idiot proof”….after all, in this case, some poor blighted backpacker might decide to actually go ahead and put a windscreen around the stove, despite the manufacturer’s dire warnings. :-)

BTW – I got confirmation I can get the analysis done on those plastic parts…though it will definitely be next week at least, and if not then, it will need to wait until early April (sorry…I have vacation coming up :-). I hope you all do not mind waiting until then.

Miguel – I share your musings regarding how the internet can connect people!

[Robert Miller]

Cushing –

I think I understand the dimensional constraints you refer to – post mold shrinkage is minimized by reducing the volume of plastic used.(?) It is a good point that I hadn’t considered.

Miguel – It is a wonderful thing!

[Eric Noble]

Another possibility is that when the plastic melts it is simply pushed into the stove by the canister pressure thereby shutting down the stove. If this is the case then when you remove the canister from the stove any remaining fuel will escape.

[Coin Page]

In my “experiment” the stove never shut off spontaneously, but rather roared along at high pressure until I closed the shut off valve. I took the stove off the canister as soon as I could handle it, to facilitate cooling. The O rings on the stove were not damaged. No gas escaped from the canister, but as I said, that canister never worked with the stove screwed in again. It wasn’t till several days later on the next hike that I put all this together.

So there was no evidence of self sealing. The thing plugged up apparently as it was cooling. The stove gave every sign that it would roar along at full throttle until the canister was empty, or catistrophic failure.

Beautiful photos. Thanks.

[Robert Miller]

Coin,

Do you have a guess as to the time it took for the canister to cool to the point you could handle it? I’m trying not to lead you. If you could describe your experience as best you can recall it would be helpful. TIA

[Robert Miller]

Eric,

The butane pressure is equal on all sides of the red plunger when the stove is on the canister.

[Eric Noble]

That is certainly the case when the stove is on the canister but turned off. I thought we were talking about when the stove is in use. Heating a canister until it fails is interesting but not nearly as interesting to me as the canister or stove heated to failure by the stove it is attached to.

[Donald Horst]

Most interesting. I hope someone does the testing or finds the information on manufacturers’ tests done under ASTM or other standards that may apply. I always like to know.

Re head volume, as most of you probably know, liquid propane expands greatly when heated, unlike water. That is why overfilling the big propane grill tanks is so hazardous, and why now they all must have float valve shutoffs on the fill connections. So head space is not constant as temperature rises. It is probably irrelevant here, because if the canisters did not leave PLENTY of expansion space for the liquid form, we would find plenty of explosion-injury reports.

But what is relevant here is that, from a practical standpoint, we don’t need to know any of this to keep from being blown up by our stoves. The warmest you need to get a stove to operate well is “cool” to the touch. If you make “slightly warm to the touch” your extreme upper limit, you will be FAR below the explosion point and the stove will work fine.

Liability disclaimer: Just remember, when you blow yourself up, I never told you it was “safe.” :-)

[Brian James]

This is why I was wondering if testing a mostly-empty canister would give accurate data…

I’m worried that if there aren’t test data posted soon, someone’s going to go squirrely and test it themselves in an inappropriate way… and I’m worried it’s going to be me!

One of our fittings suppliers will be in next week; I’m thinking of buying a stove just to show him the fitting. If I could get that fitting, it would take me 10 minutes to do a machine-charted nitrogen burst test on an empty canister… that would at least give us a baseline.

Hopefully I won’t get in the news as a miracle skin graft recipient or anything

[Coin Page]

Robert,

This was years ago. The base of the canister was pretty warm, but easy to hold, cooled by the ground and fuel evaporation. The pot supports cooled for maybe a minute until they were cool enough to hold with a cloth. The stove was a little tight coming off and took a firm twist to get started. I remember being concerned that the O rings would be damaged, but they showed no sign of smoke or melting. I think I tried touching the stove base after unscrewing, it was too hot to touch, but not so hot as to sear my skin.

Thanks for your query. It would be nice to know what the margin of safety with these things is. I’ve never heard of a canister failure either.

[Brian James]

I went to MEC tonight to look at the “Gravity MF”. One problem: no canister connection in the box, and no canister information on the box.

The “Gravity”, on the other hand, had a canister connection *only*, and included this goofy convoluted remote piezo device that looked like it was from The Sharper Image and was held on with electrical tape.

The Gravity and Gravity MF were two separate units, costing $76 and $106 respectively. One burned canister fuel *only* and the other was liquid fuel *only*.

The *burners* were in fact identical; the only difference was the hoses. The hoses connected to the burner via threaded fittings that looked like they could possibly allow for the hose to be swapped. I didn’t pull out the instructions, but it looked as though it was not a *user*-swap operation; more like a factory job with a sealing compound (likely) used. What gives, Primus?

Primus.se lists the Gravity MF as burning assorted liquid fuels plus “LP Gas”, which I took to mean canister gas. The BPL review confirms this in photos: a Gravity MF complete with canister hose, and white gas hose.

Are we getting “hosed” in Canada? Why do we have to buy two burners to get this functionality?

Brian

PS I compared the gravity to the WindPro in my hands and there seems to be no comparison. The windpro seems flimsy, flexible, and loose. It sits high and feels cheaply slapped together (for what you pay.) It seems like a “consumer” burner whereas the gravity feels “rugged”, sturdy, and permanent. The gravity feels solid like you could tie a rope to it and throw it over a tree for a bear hang — its’ pot supports don’t flex between the finger and the thumb, and it seems “purpose-built”. The WindPro, by comparison, doesn’t even have channels in the pot supports for stiffness; they are plain flat steel slapped onto a generic burner used in a lot of stove configurations for a lot of fuels. That said, lots of people use ’em and I’ve never tried either one. I’d love to see an in-depth comparo of the various remote canister stoves! My 2 cents CAD

[Woubeir (from Europe)]

I guess this could have something to do with the difference in Gravity models in 2005 and 2006. In 2005, Primus had 2 models: the Gravity running on LP and the Gravity MF running on white gas. For 2006 ther has been some name changing going on. The 2005 Gravity has become the Gravity EF, the 2005 Gravity MF has become the GRavity VF and then there’s a new Gravity MF running on both LP and white gas.

[Brian James]

Thanks for clarifying that. As anyone who’s ever bought a cellphone in Canada will attest, we live a year behind the curve no matter what technology you’re talking about.

Which I guess means that we’ll have to wait until 2010 to get this little baby:

http://optimus.se/product.asp?id=8

http://www.globetrotter.de/jpg_prod_xl/o/opt0102101a.jpg

…the new remote canister stove by Optimus (sold here by Brunton.) Folds flat, weighs 235g. It looks to have the burner from the Crux but… I don’t see a preheat coil. Maudit.

Brian

EDIT: added link to optimus.se. The stove is not actually linked from the site yet, but I guessed the product link so here it is for all to see. 9 OZ seems heavy for this thing, but I wonder if the piezo system could be stripped?

[Grzegorz Przeorski]

For my winter trips I am using stove base adapter by Markill (Vaude). It is 195 grams gadget. So it is not light but is very convinient and stable. And best of all you can use screw-on-top stove like Primus Micron for example. Works better with MSR fuel.

[Roger Caffin]

> Sigh…..looks like I need to go find a thermocouple and some thermally conductive epoxy :-) Roger: can I reserve the right to contact you to discuss what we think is an appropriate minimum remaining fuel level to preserve a vapor-liquid equilibrium under heating?

Of course! My email address is on the masthead (I think), but anyhow it’s [email protected]

[Roger Caffin]

> Primus.se lists the Gravity MF as burning assorted liquid fuels plus “LP Gas”, which I took to mean canister gas. The BPL review confirms this in photos: a Gravity MF complete with canister hose, and white gas hose.

In two words – ‘old stock’.
The original Gravity design had two versions: Gravity (canister) and Gravity MF (white gas etc). But that has been replaced as indicated in my article.

[Roger Caffin]

> One of our fittings suppliers will be in next week; I’m thinking of buying a stove just to show him the fitting. If I could get that fitting, it would take me 10 minutes to do a machine-charted nitrogen burst test on an empty canister… that would at least give us a baseline.

The fitting on ALL screw thread canisters is 7/16″ 28 TPI UNEF. Be careful, that’s UNExtraFine.
You can buy taps and dies for it from e-taps on the web. (I have).

You need to make sure the valve actuation pin sticks down far enough, that’s all. Well, don’t forget the O-ring of course. Neoprene is fine, or Viton.

And I want to know what results you get, PLEASE! Graphs!

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