The Evolution of a Winter Stove – Part 3

Billy

1. If your canister contains 20-30% propane, then when you are priming the gas coming out will be 50-60% propane, so the answer is yes, if you do a lot of priming and not much cooking then the canister will become less effective at cold temperature as the contents are used up. I don't think it will be useless tho'

2. The liquid propane and butane mix pretty well, so if the mix is 20% propane then that is what will come out when inverted.

Hi Billy

As Stuart said, if you do too much priming the canister will get low on propane.

However, if you switch to a filter disk under the jet, have the stove just a little warm before starting (body heat?), and start with a very low flame, there is little reason why you can't do the prinming thing with an inverted canister. If you are using a Powermax canister that is what you will be doing anyhow.

Filter Disk:
A recent upgrade. Cut out a 6 mm diameter circle of filter paper from either lab filter paper (I had lots left over) or use a paper coffee filter instead. You may find some sort of paper punch will give you the right size disk.
Remove jet, remove any tissue paper from inside. Check the jet is clear.
Insert filter disk into socket/hole and push down to near the bottom. It doesn't have to go all the way. It should NOT be floating loose: that would be too small.
Replace jet with just a little tightening.

It seems to me, from my testing, that this works a whole lot better than the tissue paper. It seems to catch and delay small drops of liquid fuel so they vaporise before reaching the jet. Well, works for me. Yes, this is included in the latest version of the Instructions.

I am making yet another batch of stoves, but my CNC is STILL playing up. I think I will have to replace most of the older electronics – all the motor drives. This will delay me a little, but it WILL be done!

Cheers

isobutane boils at 8 to 16 F – I don't know why there is a range given rather than a specific temperature

You said you were at 20 F, so it doesn't matter if there is less propane in the mix.

"isobutane boils at 8 to 16 F – I don't know why there is a range given rather than a specific temperature"

Jerry, since the vaporization temperature is lowered when the altitude increases, maybe that's why they state a range?

Thanks Roger and Stuart, very helpful answers.
Jerry, I have played around with the stove at 20F just because that's the lowest temps I've had to work with on my deck lately; not because that is the only temp at which I expect to use the stove.

Roger, another question:
I would like to use a windscreen around the stove and pot fairly tight around the pot in cold temps. Will the heat inside the windscreen harm the flexible fuel feeder tube?

thanks,
Billy

Roger… also…
In your instructions sheet you suggest that it's and option to start cooking/put the pot on the stove while priming.

I would add that placing the pot and windscreen actually helps to shorten the needed priming time because having the pot on top of the flame (and the windscreen in place) shunts more heat out to the aluminum plate that transfers heat to the pre-heat chamber and thus warms the chamber faster and allows sputter free inversion of the canister sooner.

does that sound right?

Billy

Roger,

How about using a bic lighter to warm the heat transfer plate and/or the pre-heat chamber in order to shorten or eliminate the priming time?

thanks,

Billy

Great question, Billy. I've been waiting for some beta testing reports regarding how efficient (priming time needed to avoid inverted flare-up) the heating-shunt design is compared to the 'traditional' through-the-flame pre-heating tube on other invert canister stoves (windpro, etc)

For comparison, my Optimus Vega with the preheat tube has never flared or sputtered and I flip the canister within a second or two of lighting the stove in upright mode (basically the time it takes to put the bic lighter down and reach over to invert the canister).

The following pic shows the Vega in use at 10f, with preheat tube visible in the flame.

So is a 3 oz weight savings with the Caffin stove worth the compromise in priming/propane conservation performance? I'm thinking mostly about this in the context of alpine use where flaring in a tent vestibule, and preservation of gas mix ratio are of high importance compared to regular 3-season hiking conditions.

> So is a 3 oz weight savings with the Caffin stove worth the compromise in priming/propane conservation performance?

I haven't noticed any compromise. The only time I experienced flaring was when the Caffin stove and canister were at -25F and I immediately inverted the canister after lighting, before placing the pot on the stove. (Producing and evaluating flaring was the point of that test, documented earlier in this thread.) By the time I reached out and grabbed the pot and brushed the snow off, there wasn't enough flaring to stop me from putting it on the stove with my bare hand, and it settled down quickly after that. The other stoves (Coleman Exponent Xtreme, MSR Whisperlite Universal) that I tested under the same conditions also flared until their pre-heat loops warmed. All three stoves seemed to take a 'reasonable' amount of time to heat up, considering the test conditions.

My normal practice with the Caffin and MSR stoves is to take several seconds to set down the lighter, put the pot on the stove, and adjust the flame before inverting the canister. This ensures the rotation of the canister doesn't flip the stove. The process takes the same amount of time for either stove. I'm in no hurry here because I'm cooking with fire near my tarp and quilt and wearing gloves–no flaring allowed. It takes the Caffin stove about as long to warm up as the MSR, so I don't find there to be a priming penalty. I have enough experience now with the Caffin stove that I don't add a priming delay before inverting the canister; it always seems to be 'warm enough' by the time I get to that point.

Since I also use best practices to maintain a 'warm' canister before I start (unlike in the above test), I always have a reasonable gas mix pressurizing the canister. Propane conservation just isn't an issue.

Added: a friend of mine has an Optimus Vega. That's a very nice little stove, way lighter and cheaper than the MSR, and it performs well. I've been recommending it.

The official boiling point of iso-butane is -11.7 C (10.9 F), at sea level. Yes, it will fall with altitude.

Cheers

that's weird, wikipedia says 8 to 16 F.

normally they give a range for something like gasoline which composition can vary

I guess wikipedia isn't perfect, you get what you pay for?

Hi Billy

> I would like to use a windscreen around the stove and pot fairly tight around the pot
> in cold temps. Will the heat inside the windscreen harm the flexible fuel feeder tube?
From page 20 of the Instructions:
'Both the Viton O-rings and the PFA hose can handle over 230 C (446 F). The rest of the stove body is metal.'
So if you can get the stove parts inside the windscreen up to 230 C, then there will be damage done. However, your chances of doing this are kinda slim!

In general, I would say that the stove parts inside the windscreen are unlikely to exceed 100 C in practical field use. If things do get start to get near 'sizzle-hot' then you should open the windscreen up a bit. I have never had any problems there.

In the snow I am happy to let the canister cop a little radiation from the stove, through the gap in the windscreen. Not a lot: just enough to take the chill off the canister. The plastics used on the canister connector should have no problems up to 40 C, which is the limit of comfort for fingers, but do try to keep all the canister end of the hose down to luke-warm.

Cheers

Hi Billy

> I would add that placing the pot and windscreen actually helps to shorten the needed
> priming time
Exactly!

Cheers

> How about using a bic lighter to warm the heat transfer plate and/or the pre-heat
> chamber in order to shorten or eliminate the priming time?
That certainly works to warm the heat shunt ('plate'), but it is not essential.

I have been using the same Bic lighter for maybe 6+ years. I will probably wear the flint out first!

Cheers

Hi Douglas

> My normal practice with the Caffin and MSR stoves is to take several seconds to set
> down the lighter, put the pot on the stove, and adjust the flame before inverting the
> canister. This ensures the rotation of the canister doesn't flip the stove. … …
> I have enough experience now with the Caffin stove that I don't add a priming delay
> before inverting the canister; it always seems to be 'warm enough' by the time I get
> to that point.
Which is what I normally do myself. Good to have independant confirmation of this.

> I also use best practices to maintain a 'warm' canister before I start
Always a good trick!

Cheers

> that's weird, wikipedia says 8 to 16 F.
> normally they give a range for something like gasoline which composition can vary
> I guess wikipedia isn't perfect, you get what you pay for?
I have no idea where the author of the Wikipedia entry got his data from. I prefer to use technical reference sites for technical data – for that reason.

Gasoline does have a very variable composition. Commercial supplies of iso-butane will also turn out to be rather variable in composition, and that will influence the BP of the mixture.

Cheers

You know, what some stoves like this might need is a flame-based canister warmer. Imagine this. Imagine a tiny-size butane cigarette lighter that you store in your pocket for warmth. When you are almost ready to light the stove, you slip the lighter into a little clamp/holder that positions the lighter into a place at the middle of the base of the canister. You light the lighter and let it burn for a minute or two. Meanwhile, you turn the canister valve and light the stove. The warmth from the lighter would last for only a minute or two, until there is some feedback heat from the main burner, and then the lighter would be returned to the warm pocket.

In the old days, we used to do something like this using a small candle flame. As long as the flame hits a good place in the broad surface of metal, it seemed to work well for temperatures around 0*F.

–B.G.–

just poking around trying to understand why they have a temperature range

I noticed that the refrigerant R600A is isobutane

on ebay, lot of 12 containers of 420 g costs $95 = about $4 per 210g (8 ounce) typical size for stoves. Plus shipping? A little cheaper than normal but not enough.

I wonder if you can buy a big container of R600A cheaper and use it to refill regular containers… Like from a refrigeration supply place?

Hi Bob

I am sure you could use a 'flame-based canister warmer', but I could not in all honesty recommend it. To be sure, experienced stove users might have no problems at all, but can you imagine what novices might do with the idea???? Terrifying!

Cheers

This is probably a dumb question, but it theoretically possible to also use this stove with white gas or kerosene like MSR's WhisperLite Universal? I'd love to have this option.

Obviously an adapter would be needed, but are there are other hurdles?

" I also use best practices to maintain a 'warm' canister before I start "

Glad you guys all agree on the above statement. But how about tell me what you mean specifically by that. (I have my own ideas, but have now idea what yours are on this)

Billy

Typically, the coldest/worst time to have to light a cold stove is first thing in the morning, so you have been camped overnight there. You can sleep with a canister inside your sleeping bag, so right away that canister is going to be just below body skin temperature. If you take it out and leave it in cold air for too long, then it goes to hell again. Getting it lit and then letting some flame heat feedback to the canister keeps it going.

Putting a canister inside an insulator during operation may not get good results, because the evaporation cooling of the canister will make it cold, but then the insulator may hold that cold in it. Putting the canister into a pan of water may help if the air temperature is below freezing. That water may have come from your water bottle, and it may have been inside the sleeping bag as well.

–B.G.–

Hi Jerry

Yes, one certainly could use R600a on a stove. It is a high-quality (ie fairly pure) isobutane. It is available in various places in anything from common pressure-pack cans to 300 kg tanks. MSR use this fuel in their isobutane canisters already, so I would argue that practical field experience says this fuel is quite safe.

The problems I can forsee with attempting to do this are:

1) The vendors sell this to refrigeration engineers, and require that the customer complete a safety training course first. After all, you are switching from a relatively non-inflammable freon refrigerant to a very inflammable butane!

2) You would need to find a safe adapter with (preferably) two valves to go from the R600a container to the canister used for the stove.

3) You would need to be able to control how much gas (liquid) you put into the canister to avoid over-filling it – which could lead to an explosion in hot weather if you fill to 100%.

4) All the canisters are rated for a single use, with refilling legally banned. My personal opinion here is that main reason for this is that the authorities are terrified of the idea of amateurs refilling a canister, and I can't blame them. A secondary reason could be the problems you would get with rusty canisters: they may not seal properly at the external O-ring.
That said, I note that you can legally buy the adapters in Japan, so maybe they don't have such a ban there.

Disclaimer: neither I nor BPL advocate refilling canisters, for obvious reasons.

Cheers

> [is] it theoretically possible to also use this stove with white gas or kerosene
> like MSR's WhisperLite Universal?

In practical terms, no. The problem is that the boiling point of white gas is much higher than the feedback from the Heat Shunt can sustain at the stove body.

The Heat Shunt is sized to keep the stove body a bit above 0 C, which is fine for butane and propane, but white gas needs a temperature of over 150 C. Kero needs even higher temperatures.

Cheers

> " I also use best practices to maintain a 'warm' canister before I start "
> tell me what you mean specifically by that.

See Bob's reply.

Cheers