Mt. Whitney Portal Store & Hostel Forums General Mt. Whitney Portal Store Message Board Does Gas Have An Expiration?

EP - the gas canisters follow Raoult's Law. Total pressure equals the sum of the pressure of each component times the mole fraction:

P=P1X1 + P2X2

Where P1 is the vapor pressure of component 1, and X1 is the mole fraction of component 1, and P2 is the vapor pressure of component 2 and X2 is the mole fraction of component 2. The graph that you have from the MSR website shows only total pressure, which drops as the gas is consumed and the mole fraction of the component with the higher vapor pressure (propane) decreases. And that graph clearly shows the superiority of isobutane over butane.

Looking at that graph, you can see where the curve starts leveling off as the canister nears empty, it is at that point that the remaining fuel is almost entirely isobutane (or butane, if that is what was in the original fuel mixture).

lambertiana - you've got it right, or close enough anyways. But you see that graph differently than I do. Where you say there is almost no additional pressure due to the propane I still see some left. The IsoPro curve is almost a linear decline. I'll take that extra little bump in pressure when camping in the cold, thank you.

The butane based canisters aren't as good. I used to use Campinggaz, the old bayonet removable attachment canisters. They are (or at least were) propane/butane mixes and were sometimes a challenge to use on ski trips.

SAFETY NOTICE;
Propane & Butane are HEAVIER than air. So if you are cooking inside your tent and have a leak of any kind, the gas will 'pool' at ground level. The LPG (liquified petroleum gas) available at commercial outlets is 'blended' throughout the year to suit local temperatures & geography. During the hot part of the summer it will be almost 100% butane, so if you fill up a 5 gal. tank for the barbeque and try to use it in the winter it might not work. These gases are all by-products of the gasoline distillation process, propane costing more than iso-butane and butane. They are the fuel used for interior fork lift operations because they burn so clean.

Unless they are illegal:

http://www.nps.gov/yose/planyourvisit/wildregs.htm

"Can I use a Sierra stove above 9,600 feet?
No, you may not use a Sierra stove (stick stove) above 9,600 feet in elevation. The small twigs used to fuel Sierra stoves are just as valuable a part of the ecosystem as is the larger wood used in traditional campfires. Regrowth at higher elevations is extremely slow and the soil is low in nutrients. Removing this wood from the system further slows growth."

In other words, they treat it like any other wood fire. And I don't think they allow carrying wood up from lower elevations for a campfire either.