Regarding pump-based generators, I have found that it is important to build the MAGMA pump first and the WATER pump second.
WATER + MAGMA = STEAM....
MAGMA + WATER = OBSIDIAN!!!!
Interestingly, both processes destroy both inputs in my experience.
Here's some ASCII of a working cave-in generator based on pumps (built in 34.04). With controlled volume inputs, you can generate a single cave-in and thus wire it up to pressure plates, etc...
Z+1 (# = wall, * = gear, | = axle, . = floor, = empty space)
Gears support the screw pumps from above. Axles support the gears which are not on floors. Floors are channeled out to provide power to pumps and prevent overhead support for the obsidian. You can build bridges over the central gap if you like.
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##* *##
##| |##
##|.|##
power from somewhere over here...
Z=0 (M = MAGMA, W = water, sS = screw pump (inputOUTPUT))
Obsidian will form between the pumps then collapse (as long as there is no support NSEW on this Z or Z-1 or Z+1)
Output end of screw pump is not on a floor. It is channeled out and supported from above by the gear.
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MsS SsW
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Z-1 (key is the full cross pattern of empty space - you can have more empty space if you want...) (the other key is open space one Z level below the pump input to draw from!)
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M# #W
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Z-2 (channel on left for obsidian to fall into, channel on right for things to get knocked into by cave-in! Make them nice and deep. Some things will fall on the left as well but most will be blasted right.)
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