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Gas Canisters Calculations

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Gas Canisters Calculations

Postby maverick » Fri Jun 06, 2014 1:49 pm

How do you estimate the amount of fuel you have left, or the times you will
be able to boil water for your freeze dried meal? Over the years have met folks
who swished the gas around and estimate, those who weight the canister, and
those who know how many boils they get per canister from experience, marking
down the boils after each usage. Which category do you fall under, or do you
have your own method? Have you ever miss judged and could not cook your
dinner?
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Re: Gas Canisters Calculations

Postby longri » Fri Jun 06, 2014 2:23 pm

I just shake it. It's not highly precise but good enough. I can't calculate boils exactly because conditions change. And sometimes I'm not paying attention and it boils longer than necessary. And yes, I have run out of fuel although this has usually been because I screwed up and didn't take enough to start with.

One option is to float the canister in water. You can figure out in advance (using a scale to calibrate) where a canister floats at different fill levels. MSR canisters now even come with the float level printed on the side for empty, 1/4, 1/2, 3/4, and full, just like a gas tank. I think you have to be careful and burp the air from the concave bottom.

If you're OCD you could carry a pocket scale. Mine weighs 120 grams and is quite durable. I'll bet there are lighter pocket scales that would work. If you carry a fishing scale (do people do this in the Sierra?) you could use that.
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Re: Gas Canisters Calculations

Postby ucangler » Fri Jun 06, 2014 5:02 pm

Greetings!

My trips are short and due to work (self employed) prolly will never get a chance to do something longer than 1 week. Plus, don't want the wife to be alone for that long :(

For my jet boil flash, I always have 1 brand new canister (small) in my pack regardless of what is in the gas canister used before.

I believe 1 canister (small) can boil 48 cups which last me about 8 day.

I'm the kinda guy that maybe takes a little more things than needed with me expecting worse case scenario.

Id rather have something and not use it, then need something I don't have.
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Re: Gas Canisters Calculations

Postby sparky » Fri Jun 06, 2014 7:06 pm

all my half full canisters I take car camping to empty them out. I think I have ran out a time or two, but not for a long time. 1 can lasts me 4-5 days depending. I like coffee, and cheese quesadillas!
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Re: Gas Canisters Calculations

Postby freestone » Sat Jun 07, 2014 5:52 am

I am new to canister fuel after using alcohol for many years and white gas before that. Glad to see how other folks do this. Currently I measure how many grams it takes to boil 2 cups of water at sea level, then calculate how many boils I can get per canister, but in reality, I take one old, and one new since most of my trips are short. What I find frustrating about canisters are the long boil times as the canister becomes empty. Is that normal?
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Re: Gas Canisters Calculations

Postby fishmonger » Mon Jun 09, 2014 9:45 am

freestone wrote: What I find frustrating about canisters are the long boil times as the canister becomes empty. Is that normal?


two things - keep the canister as warm as possible, especially when it gets close to empty. And much more importantly, get something that's a propane/isobutene mix, not the cheap stuff (as in Primus)

http://zenstoves.net/Canister.htm - look under fuel mixes to see what difference that makes in boiling point temps (as in when the stuff evaporates and comes out of the canister). Lots of other interesting details about fuel mixtures and canister weights on that page.

Another issue can be the stove efficiency. I've gone through several stoves, done a lot of measuring and testing at home and in the field, and have settled on the Jetboil Sol with various pots (when alone the small one, when in a group the Sumo cup). Using Jetboil and SnowPeak (Gigapower) canisters, I really barely notice the end of the canister even on cold mornings at high elevation (as in April on Whitney). Those have a really high ratio of Propane to Isobutane and no butane at all in them. Butane is the stuff that doesn't evaporate well when cold. Propane pure is too dangers.

Near the end of the canister, you'll notice how cold the canister gets due to the pressure drop inside. If it isn't totally empty and you need to use it again, keep it in the sleeping bag overnight, or warm it up in the sun if available.

For the really cold trips, I use a Jetboil Helios, which allows the canister to be used upside down, pushing fuel out of the canister at very low temperatures, much lower than any upright canister stove will allow. It's just a little heavier than Jetboil Sol with Sumo pot, so I don't bring it in summer.

Jetboil Helios in use at Outpost Camp on Whitney in April - water was frozen solid in there overnight. Note upside down SnowPeak canister and ice on the black lid in front of it.

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Re: Gas Canisters Calculations

Postby longri » Mon Jun 09, 2014 10:14 am

freestone wrote:What I find frustrating about canisters are the long boil times as the canister becomes empty. Is that normal?


Annoying and unavoidable to some extent. As Fishmonger said buying a canister that has isobutane instead of butane helps a lot. The thing that bugs me most about canisters is the canisters. They're bulky and heavy.
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Re: Gas Canisters Calculations

Postby hikin_jim » Wed Nov 05, 2014 3:06 pm

longri wrote:The thing that bugs me most about canisters is the canisters. They're bulky and heavy.
Yep. I ran some numbers, and even on longer trips (2 weeks without re-supply), alcohol stoves are almost always lighter in the end (and if a canister stove is lighter, it's by less than an ounce). If anyone is interested, my numbers are here: Which is Lighter – Alcohol or Gas? It's that steel canister that kills you. The smallest size weighs almost a quarter pound, empty.

HJ

P.S. The Excel spreadsheet at the above link is yours for the asking if you want to run alternate numbers.
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