I have a trangia 500 fuel bottle with(because of) the safety spring cap: I have noticed if it is filled with meth somewhere colder, then brought somewhere warm, or just gets warmer, some pressure builds up resulting a surprise spurt when top button depressed...I gave never noticed anything related in the 500ml bottles uk meth is supplied on? Forewarned is forearmed, but I wonder why I never noticed any effect from the suppliers disposable bottles?
Perhaps the disposables are able to expand and contract enough to mitigate the pressure change, while the rigid bottle just pressurizes.
After numerous times experiencing the fuel "spurt" due to pressure and/or temp changes when trying to fill the burner first thing, I developed this habit years ago, and subsequently haven't experienced the fuel "spurt" since: Stand bottle upright, unscrew the valve button. Do not initially hold the bottle in the "pouring" position. Depress the release valve button for a second or two. With no fuel up against the valve, the only thing "released" is air pressure, and no fuel is gonna go spurting out. Release the valve button. Hold bottle in pouring position, press valve button/pour, release button when burner (or whatever) is filled. Side note: after you're done pouring, there could be a little bit of fuel remaining in the "nozzle" of the release valve. Again, position the bottle upright, depress the valve button for a few seconds, and those few drops of fuel will go back into the bottle (notice how the "nozzles" are tapered).
Got reminded about venting the Trangia bottle before pouring this weekend. Definitely vent while upright.
