For the check-valve to do its job of preventing beer having a bit of an unscheduled ferment one "early hour of the morning" and the pressure pushing several pints of beer over the floor (or if attaching any vessel with a tiny amount of pressure in it), you need to put the check-valve in the wrong-way-around. Err ... the problem with that should be obvious! Okay, so you put the check-valve the right way around and beer comes out the pump again. Now at least beer that's been in the pump since last month, open to the air, (for example), can't accidentally run back into the container and ruin the contents. But if any pressure appears in the container, its beer over the floor again.
You need a "demand valve". Full-stop! ... Oh, alright, I'll explain a little more:
"Check-valves" used to be somewhat under-engineered, and before they allowed anything through there had to be enough pressure to open the valve ... it is known as the "cracking pressure". For many years now the improved manufacture reduced "cracking pressures" greatly. There is no problem making "check-valves" with higher cracking pressures of anything you want. But there are already devices now that can do that cheaply ...
... they're called "Demand Valves"!
History being history ensures the old name lingers on well past its "sell by". So, we call "demand valves", "check valves" ... well at least in that particular context.
More cobblers from the King of Cobblers, Anywhere! The only people who want to argue with me are even more deranged than I am! (It took me months to figure all that out ... plus a few aborted attempts to use an actual "check-valve"!).
