Now, now....this is getting really interesting. I just "happen" to have some level of access (please do not ask any detailed questions......) to some pretty sophisticated polymer testing equipment. It might be worth disassembling an empty cannister, taking a close look at the valve assembly, and thermally testing parts that would appear to be most succeptable to thermal damage/degredation. No promises....as this would have to be done in a way that does not interfere with the normal workload on the equipment.......but it just might be very easily done.....

Robert - could you manage to get some picts that make it really clear how the parts are laid out inside the valve?

Edited by chamlen on 03/22/2006 12:27:43 MST.

Detail of blue plastic valve. Approx 1/4" dia x 3/8" long. Its function appears to be a guide for a spring. It is crimped into the sheet metal.


Detail of inside of blue plastic valve. At the bottom is a red plastic piece with a slot approx 0.090" deep across it. The red color is the same as the pin in the screw on portion on the exterior of the canister. I think it is reasonable to assume this is the same piece of plastic but cannot confirm absolutely at this point. The deformation of the blue plastic was from my attempt to dislodge the blue plastic from the canister.

Edited by procab on 03/22/2006 12:40:44 MST.

Seeing the metal liner in that plastic button makes me wonder if the canister could self-seal in the fashion that I proposed.

Do you see any other possible seal-off mechanism? Perhaps the needle in the needle valve is made of a fast-expanding material such that it expands to seal itself when the temperature is too high?

Now I'm definitely interested in an oven test. I'd love to know what happens to each component of the valve all the way up the temperature scale. I also wish I owned canister equipment so that I could deplete a canister and cut it apart! (And that I wasn't at work...)

Cushing, I'd be interested to know the makeup of the polymers in various brands of canisters; do post!

Brian

Unfortunately (because this is a more expensive proposition), we also should ask about the plastic components in the stoves themselves....unless we can obtain them via rebuild/maintenance kits.

I'm estimating the red plastic piece is 1/4" tall. There isn't much room for more pieces. The slot in the red plastic I believe is revealing. It allows the gas to bipass while keeping the majority of its circumference in close proximity to the steel to facilitate heat transfer.

This is a good point. I've heat-damaged a piezo igniter module from windscreen use, and am a little curious about those o-rings.

Better canister stoves seem to have mostly metal parts, other than the o-rings.

So Rick - this begs the question as to which are the better stoves.......?

At this point I'm thinking of extracting the red plastic piece, measureing it and throwing it in the oven. Any input would be appreciated. I've got some paperwork to do and will check back in a hour.

Edited by procab on 03/22/2006 14:57:19 MST.

Yes please :)

But do two side-by-side tests: one all by itself and one still-intact valve assembly as shown in the picture.

I look forward to the results!

Edited by bjamesd on 03/22/2006 14:50:28 MST.

I don't think I can do two tests. I think it will be beneficial to cut a pie section out of the cartridge and lindal valve so you can see exactly where the parts are in relation to each other. This will make it impossible to do the intact test. I only have the one cartridge.

Besides Brians original idea that the red plastic piece would expand to shut off the gas flow I see another point that may be a better alternative. There is a steel probe in the bottom of the stove that inserts through the lindal valve and presses on a corresponding probe on the red plastic piece to allow the gas to flow. This narrow plastic probe with spring pressure from the blue sleeve could easily deform if the metal probe were to become too hot.

Both ideas can be tested in one bake.

Has any one seen my Dremel?

Robert - does that blue plastic piece appear to actually be strong enough to compress the spring? If so, it could both be holding the spring in place, AND acting as a heat-sensitive element that when hot enough will fail to hold the spring back, and cause the flow of gas to halt......

The blue plastic piece is both guideing the spring and transfering the tension from the lower end of the spring back to the canister. It appears to be only in contact with plastic parts that I doubt would tranfer any appreciable heat to enable its failure.

UPDATE - plus if the spring loses tension the valve goes full open. Stand Back!

Edited by procab on 03/22/2006 16:18:25 MST.

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

Edited by procab on 03/22/2006 16:42:51 MST.

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?

Edited by bjamesd on 03/22/2006 16:47:00 MST.

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.

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.

Edited by procab on 03/23/2006 00:45:11 MST.

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.

Edited by chamlen on 03/22/2006 20:35:15 MST.

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

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.

Edited by procab on 03/23/2006 07:49:26 MST.

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?