Re: Vacuum
you might be able to duplicate what happened with a simple experiment
a) pressurize a plastic 2L bottle somehow [specia cap?] using something that's close to its condensation point, like a refrigerant gas.
b) release the pressure rapidly [it will cool the bottle slightly]
c) quickly seal it after venting (a check valve might help)
d) watch the fun
note that gas velocity through the valve will draw a slight vacuum if the valve closes rapidly, due to momentum, depending on the length of the pipe involved. And it cools the place where the gas once was, even more effectively if it can try and condense into a liquid afterwards (like refrigerant).
similarly, (don't try this at home - gutless disclaimer) lighting off alcohol vapor within a 2L bottle through a 9mm hole in the cap might give you a similar effect (it also makes for a fun rocket - distance and safety precautions apply). The velocity of the escaping exhaust through the cap literally draws a vacuum behind it, and the bottle (which quickly cools down the remaining gasses and they have lots of water vapor in them) implodes a bit.
Also...
Rocket fuel tanks are designed to be pressurized because that gives the entire rocket more structural strength, gives positive head pressure [stop it you with dirty minds] for the fuel pumps, and also PREVENTS the 'implode when the pressure drops too low' problem, particularly on launch where compressive stress would otherwise 'accordion' the rocket.
Biting the hand that feeds IT
