Quote:
Originally Posted by GaryVoshol
Jason, I believe you've just described the process behind a double-expansion steam engine. There are triple and quadruple steam engines still in existance today. Each cylinder in sequence is larger, being driven by lower pressure, so that the steam from the boiler is used 2 or 3 or 4 times, making the engine more efficient.
Just a sidebar, nothing to do with the original pneumatic question.
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Actually it is quite relevant to the original question and an excellent example of recovering energy from a "used" gas. I seem to recall something from third-year thermodynamics about maximizing energy recovery from a compressed gas, and that if you could expand the gas infinitely slowly that you could recover 100% of the energy. (Those with more recent memories of thermo, please feel free to correct me... it was almost 20 years ago...) So the more stages that ocurr in the expansion process the more efficient the energy recovery from the compressed gas.
In this case it would also be interesting to use a constant pressure, rather than constant volume, compressor. The low pressure side of the system could be fed back into the compressor so that the air would only need to be compressed from 30 psi to max, rather than from atmospheric to max.
Jason