# Backpacking Canister Stove - Canister Pressure at Altitude

1. Mar 9, 2013

### Dexters

I'm raising these two questions based upon something I read on Backpackinglight.com - see link #1 - having to do with the internal pressure of fuel canisters filled at sea level and used at 6,000 feet.

The first question has to do with the boiling point of n-butane used in the test - see link #2

Temperature: 31F/-0.5C as measured on a digital probe type cook's thermometer. No calibration was employed on the thermometer.
Boiling point of n-butane at sea level: 31F/-0.5C
Boiling point of n-butane at 6,000'/1800m: About 19F/-7C

Question 1 - What was the boiling point of n-butane the canister?

Question 2 - Can anyone explain the canister pressure equalization disussed below? My gut tells me that the effects of altitude would have little effect on the internal pressure of the canister because of the rigid nature of the canister.

Paul Mason wrote: > What about the issue of the n-butane being in a canister? For the inside pressure of the canister to equal the outside pressure; wouldn't the volume/size of the canister have to increase while the amount of the fuel inside remained the same?

If my understanding is correct there is a 23% decrease in air pressure from sea level to 6,000ft.
http://www.endmemo.com/physics/pressurealtitude.php

If, I'm correct that means that the n-butane was below or at the borderline of its boiling temperature during the test.

Paul, the key difference in pressures is the relative difference between the inside (the canister) pressure and the outside. As gas is drawn off, pressure starts to equalize between the inside and the outside. At the point no more gas issues forth, the pressures are equal. Ultimately, it is the ambient air pressure and canister temperature that determines how much flow you'll get from a canister.

Link #1 - the bottom video is long but shows everything

Line #2

This is what a fuel caniste looks like - not used in the tests.

http://www.rei.com/product/643061/snow-peak-giga-power-fuel-canister

Here is more on canisters and the effects of cold.

http://zenstoves.net/Canister.htm

Last edited: Mar 9, 2013
2. Mar 11, 2013

### CWatters

I haven't the energy to go through all the links but...

Correct. If the temperature of the canister is kept the same the pressuer will stay the same.

However if the temperature of the canister falls then the pressure inside will fall. Especially if the temperature gets below the boiling point of the Butane.

Its well known that butane is usless in cold weather and many people use propane or a mixture for that reason.