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« on: August 22, 2010, 12:54:48 am »
Infinite water and drains can be problematic for traps, especially ones with a short cycle time like yours. Pump circuits are much more reliable; if you're clever you can refill what gets lost to spillage automatically via a diagonal connection to a lake or similar, and you don't have to worry about flow mechanics slowing down your fluid input. If and when I build such a trap, my "capacitor" reservoirs to make sure i have enough water for constant operation in variable conditions are typically larger than the rest of the trap combined.
consider the following setup in a top view of the only real level on which it operates:
Walls--------------/--------Walls
XXDPPPPPPPPPPPPXX/XXLXUFp to fort
Walls--------------/--------Walls
where L is the pressure plate that turns on pump stack p, causing it to flow water through fortification F, past upward staircase U leading to the rest of the fort, along a corridor of variable length -/- to reach the pit trap newly revealed by retracting bridge P, the bottom few z levels of which are filled with enough water to fill the corridor from F to the start of P. The entire siege will be either washed into the pit or drowned if flow mechanics refuse to move them, but they won't path through the water flow to staircase U. Once everyone is washed off of tile L, the pump shuts down and the bridge closes, and the goblins either flee or are already drowned. The water level in the pit below P is still what it was before the run, so next time L is triggered there is water ready to flood. Furthermore, the drain and flood machinery are linked, so if, for example, a goblin's pet giant olm smashes a pump, the trap is merely inoperative, not a danger to the fort. This is further assured by drain D, a simple floor grate in case something odd happens with the pressure plate and the bridge isn't open while the pumps are running.
Similar degrees of safety can be achieved by creating a constant drain away from your infinite source, but at the cost of a tunnel to the map edge; all local systems have a chance for catastropic, fort-flooding failure, particularly if the source is gravity fed and could teleport water up staircase U into the fort.
Incidentally, it's possible to make the above even more foolproof by having the pit trap be beyond a staircase arrangement similar to staircase U for entering the trap corridor:
Walls--------------/--------Walls
PPPXuXXXXXXXXXXXXX/XXLXUFp to fort
Walls--------------/--------Walls
This is the setup at work in my own fort, albeit with a short circuit to pull water from the higher levels of pit P around the walls to pump p.
EDIT: both designs can have grates installed to shorten the drop but allow your trap catches to wander into other traps.
Hope this helps.