quoted by Benzonline
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hydraulic or pneumatic system including the control mechanisms and any advantages or disadvantages you see in the system when compared against some other system (say a mechanical system).
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I have always considered hydraulic or pneumatic systems "mechanical".
You can move a lot of BIG stuff with a properly designed hydraulic system. Way back before all the electronics were established in industrial control everything was done using pneumatic control systems. A 3-15 psi (in some applications 3-27) signal equaled 0-100% signal. The signals were used to position pneumatic damper drives, control valves, steam drum water level and turbine speed controllers in addition to providing the 0-100% "signal" to indicate anything from feedwater flow to steam flow (as applied to a utilities boiler). Like the old Benz with the vacuum leaks the issues that usually came up with these old robust systems were - you guessed it - leaks
. As long as you kept the compressor running you could run the boiler. With the way boilers and plants are run today you would not be able to stand the "inaccuracies" associated with a pneumatic control system.
I use the attached site from time to time and you can probably find some pretty good info in there.
good luck