I am filling my castle moat with hot molten magma, which comes from a pipe that extends many z-levels above my fort and the layer of my moat. I am of the understanding that, if I were to simply tap a channel straight into this pipe with no cut-off, then the magma will keep pouring out until it fills my moat and then overflow and destroy the world, no? Or is the lack-of-pressure thing enough to keep that from happening?
Regardless, in the interests of !safety! I decided to put in an extensive cut-off system, all of it made from gabbro or alunite, including the mechanisms. I built a raising draw bridge raising up towards the pipe, and raised it. In the space next to it, I built a wall-grate. In the next square, I built a flood gate. I then built a second draw-bridge raising up away from the pipe. Now once my system is full of magma, I can raise both bridges and make the gate-system impervious to building destroyers.
But it didn't work that way.. I dropped the bridges and opened the grate and the floodgate, and used the busy-to-leave method to mine out the last square, opening the pipe. My legendary miner high-tailed it out of there, and the magma was hot on his trail.
But it SWEPT THE FLOODGATE AWAY!!! There is a gabbro floodgate with an alunite mechanism making its way down my chamber. Is this fort lost? Can I ever seal the chamber again? Especially in light that draw-bridges are not supposed to block fluid for much longer (if they still do).
WHY did the magma sweep away my flood-gate?? For Armok!
I will add that I cleared the chamber of stones first...