longri wrote:Where did you get this grainy chart that you included in your blog?
That's from an old climbing magazine from the 70's called "On Belay". I had seen a lot of talk about how the vaporization (boiling) points of gasses are affected by temperature, but I hadn't seen a lot of talk about the effect of elevation. My "How Cold Can I Go?" post was written in part to emphasize the affects of altitude. It probably doesn't matter much if one is living in Florida (the highest point in Florida, Britton Hill, is only 345' above sea level!)
but for us Californians who regularly travel above 10,000', it's a significant
difference -- as in 20 degrees Fahrenheit. In other words, if you can operate a particular stove with a propane/isobutane fuel mix at 20 degrees Fahrenheit at sea level, you can operate that same set up at 0 degrees Fahrenheit at 10,000 feet. THAT'S COOL!
No one was talking about it, so I did. And that graphic was illustrative albeit old. In a way, I chose that graphic on purpose, just to illustrate that the concept had been around for a long time. We just need to reincorporate it into our thinking. It's not just a matter of temperature and fuel type. Elevation (really air pressure, but that's highly correlated to elevation) must also be considered. Now, is the graphic, precise? No. But it communicates the idea very effectively.
longri wrote:Assuming you need between 5 and 10 psi gauge pressure for acceptable stove operation...
Actually only about 3 psig is required for decent pressure on an upright canister stove. Keeping the fuel temperature about 10 Fahrenheit degrees above the boiling point of the fuel mix should be sufficient to generate that pressure. Your stove won't necessarily be screaming at maximum, but it'll be decent. For an inverted canister stove, you can get by on as little as 1 psig. You just need enough to get liquified gas to the generator (i.e the "pre heat loop").
longri wrote:the last time I camped above 13,000 feet in the Sierra in mid-winter it never got below 20°F.
Wow, that's warm. I've camped in the teens in lower elevations than that. If you're not getting below 20F, then bringing an inverted canister stove isn't absolutely necessary, but God help you if the temperature drops unexpectedly low. Of course at 13,000', you've got a lot of "slack" because of the low pressure which depresses the vaporization temperature of your fuel. And you'll do better with a fresh canister with an upright canister stove since the propane content is still fairly high when the canister is full.