Subject: Has anyone designed hydraulic logic gates or a water-logic computer?

I have this crazy notion.  I would like to see a computer, which instead 
of using electricity, uses logic gates operated entirely by water pressure.

Maintain a sufficient head of pressure, and implement a simple system 
clock with a water wheel and valve.  Some logic gates are simple, using 
water pressure and valves with springs.

Anyone heard of anything like it?  Anyone want to have a go?

Re: Has anyone designed hydraulic logic gates or a water-logic computer?