okay, I'm trying to build a magma-lock system >> the idea being that in uber emergencies, my dwarves can throw a switch, and all the compartmentalized parts of my fort will seal themselves. Then I can just have my miners burrow back through to the safe areas to keep the fortress running, while all the nasty demons and forgotten beasts are safely locked inside their own tiny compartment and unable to get out.
The system is simple.
have magma-safe 4 flood gates. These lock up a 2x2 area so that water and magma can't flow into one another inside of it (this would be the small halls connecting compartments of my fortress), when released, four more pop up locking the area in and allowing the water and magma to mix and form obsidian in those 4 squares. The make up of the squares makes it VERY unlikely that the hallway won't be completely sealed (diagnols and all that) so it all works for the best.
My question is this. If the magma and water mix together and form obsidian where the floodgate is. Does it have to be mined out in order for the floodgates to close? If so, I'll need to add some interior flood gates (or pumps or something) to control the amount of water and magma released into the magma-locks and ensure that the obsidian can be mined safely without having to worry about losing miner and dwarves as the excess floods out into the chambers >>