One of the questions I asked when interviewing teams for machine awards, especially anyone using pneumatics, is:
How do you determine the approximate force of a piston.
A lot of teams couldn't answer.
A lot of teams looked up the answer on a Bimba chart
Some actually answered with piston surface area x air pressure which was what I was looking for.
A more detailed answer can be found here:
http://www.engineeringtoolbox.com/pn...ce-d_1273.html