I believe the word you're looking for is valve. I'd love to see those. (Perhaps even configurable 'this way'/'that way'/'block all'?)

When ghost building (Shift+LMB) a locomotive on ghost tracks factorio froze up making windows ask me if I wanted to close it.

Microsoft Windows 7 Professional UK [Version 6.1.7601]

Savegame link

In answer to the OP: I tried to make a logical network to only let a train leave when it's full: i made a train crossing just after the filling station, blocking (with a signal) the main rail, and once the wagons are fully loaded, put only one wood into the train that's driving on the circle "...

New to the game, I've finally reached the point of oil trains w/o being bitten to death. Now, my oil pumps are so slow they can't fill up 1 wagon within 200 seconds, I'd like to not waste my train running back and forth carrying only empty drums in the back wagon.. short of removing the fuel, is the...