How does a pressure vacuum valve works on tanker ships?

Answer 1

It is merly a valve which will open when pressure build up above a certain pressure OR opens when pressure drops below a certain pressure(creating a vacuum).

Answer 2

Yes! The gunpowder and explosive material in the primer already contain all the oxygen they need; they'll ignite and burn quite happily with no external source of 02. Consider how tightly a bullet is clamped into its casing – how would free oxygen get in there anyway? Temperature, on the other hand, could be a problem. People typically think of space as cold, but in fact space, being a vacuum, essentially has no temperature at all. Objects in space may get very hot or very cold, depending on their proximity to the sun and their reflection coefficiency—basically, their tendency to reflect radiation rather than absorb it. It's certainly possible that a handgun way out in the middle of interstellar nowhere might become so cold that the gunpowder in the cartridge no longer reliably ignites and burns fast enough to produce an explosion. That’s not a result specifically of being in space, though, but simply of being very, very cold. As far as shells being airtight, some (mostly military) rounds are sealed. The Soviet SPP-1 is an underwater pistol. They also had a APS underwater assault rifle.

Answer 3

Try this link for an explanation of how pressure relief valves work -- I think that will do it.

http://www.dynamicair.com/products/reliefvalve.html