Canister stove question

Normal when a canister goes to empty.  Last liter boiled takes 2 or 3 times as long.  2nd to last liter takes longer too.  It’s worse if it’s cold, getting down to the minimum temperature for that fuel.

Try a new canister.

I have a pocket rocket.  It works pretty good.  3 minute boil.  I got a Soto Windmaster for free which I like a tiny bit better, else I’d still be using the pocket rocket.

It seems that you are observing normal behavior.  Test results for two cups of water in the link are consistent with your increasing boil times for one liter as the fuel is depleted.

https://tinyurl.com/y9ll97oo

Usually you are using a larger proportion of propane to start with. This will burn hotter, with greater pressure. Later, they may be none, decreasing pressure. I believe this is what you are experiencing. It is rare for a topper to get plugged.

Hi Karen

Read https://backpackinglight.com/effect_of_cold_on_gas_canisters/: this will explain everything.
Yes, your canister ran out of propane and was too cold to vaporise the butane.

Cheers

not that it’s all that important, but the propane is mostly gone after about half the canister is used up, according to the Roger (Robb?) spreadsheet.  This does not explain why the last few boils slow down so much.  This does explain why in cold temperatures, like less than 32 F, the first half (or 1/4) of a canister will be better if it starts with a significant amount of propane.

when a canister gets down to the last little bit, since there’s so little butane, it’s thermal mass is much less, so to provide enough heat to evaporate, the butane will lose a lot more temperature.  Even if the air temperature is fairly warm, the butane will lose enough temperature to go down approaching its boiling point, thus it will slow way down

another factor is that if the canister contains isobutane and N-butane, the isobutane will preferentially boil away leaving almost all N-butane which has a higher boiling point.  This only happens when the canister gets down to about 10% full or less.  According to the Roger spreadsheet.

When I’ve wandered through the REI recently, I noticed that all of the canisters said they had isobutane and propane.  I don’t think they used to specify that.  Maybe the canister manufacturers are now making an effort to reduce the amount of N-butane.  MSR Isopro says it’s less than 5% N-butane.  Of course, just because it says it has isobutane doesn’t mean it doesn’t actually have a significant amount of N-butane.  It would be very difficult for a user to notice the difference.

when a canister gets down to the last little bit, etc
Just so.

just because it says it has isobutane
It is a sad state of affairs when customers are reduced to not believing the labels any more. Understandable though.
Looking at those cheap ‘fly-spray’ cans of butane – I suppose the vendors are actually being honest. The contents are butane – percentages (wisely) not specified. Fair enough.

Cheers

The last time I used it, it took more than 10 minutes to boil a liter of water. Not bad conditions, warm, dry and just a small breeze. Pretty sure this wasn’t how it used to operate. I just tested it on my deck with very little wind, and using an old canister, and the gas ran out in 9 minutes, no boil achieved.

Hmmm.  Well, I see a lot of talk about cold and propane content and such, but Karen I believe said that it was warm.  Unless Karen lives in the very far north (or far south for that matter), warm usually is going to mean upwards of 15C/60F, if not warmer, perhaps even 20C/70F.  At those temperatures, it shouldn’t matter if the can were 100% butane; it should work fine.

However, as has been pointed out, near empty canisters sometimes do funny things.  I’d get a new canister and try it out.  I think highly of the MSR brand, but it shouldn’t much matter if you buy any major brand and it’s “warm” (well, except perhaps Coleman which sometimes has trouble mating with non-Coleman stoves).  Even if you do buy a new stove, you’ll still need a new canister, so no loss there.

Please let us know how it works out.

HJ

Canister stoves slow way down when they’re almost empty even if it’s warm.  Like the last liter or two of water boiled.

If I’m in a hurry I’ll just swap in a new canister, or wait 5 or even 10 minutes for it to slowly burn out.

Now-a-days, I just refill and have enough fuel in the canister so it never runs out.

So reporting back much later – must have been a problem with the canister because since then, I’ve used the Pocket Rocket many times, with multiple other canisters, and it has been fine, about 4-5 minutes to boil in less sheltered areas and a bit faster in a hiker shelter (all partly used canisters, since I scrounged some).  That system works well for 2 of us, however I did decide to get a Windburner for solo use. It is 4 ounces heavier total than the pocket rocket/pan combo, but if I skip bringing a bowl and cup and use the integrated one with the Burner, I’ll come out ahead about one ounce. More critical though is that the Windburner is compact, taking up less width than my pan. I think that will work well, especially if I need a bear barrel.

I have only tested the Windburner at home so far, and immediately burned my hand grabbing the wrong part to get the pan off the burner, doh. Good reason to test at home first! User error, to be sure, but I’m still going to call the stove the Handburner. Other than my own mistake, I like it, it was 2 minutes to a full boil, easy to pour. Not sure the pot and cozy will work for keeping food hot off the burner. I may make a separate better cozy for it, since that’s how I usually cook.

I occasionally get a canister like that, even worse when using “flyspray” canisters, just the luck of the draw s perhaps?

Take some tinned Spam along and you could call it the Hamburner?

The crimping machine which attaches the Lindal Valve fitting to the canister can sometimes malfunction just slightly. I have seen this before. When it does malfunction the pin on the stove may not depress the valve itself enough.
I am not saying this happened here, just that I have seen it happen.

Cheers