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Originally Posted by Andy Baker
When sizing a pneumatic application, another thing to think about would be side loads and efficiency losses.
For instance, working from the numbers Chris posted above, there are many situations where you will not get your entire 176 lbs (retracting) for a 2" cylinder at 60 psi. If the rod of that cylinder is experiencing any side loads, then more friction is created inside of the cylinder. A certain amount of force is needed to overcome this friction. This amount may be up to 1/4-1/3 of the force of the cylinder, if the side load is significant. Therefore, cylinder output forces in these situations could be only 70% - 80% of your calculated force.
Andy B.
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I will go further and say that there is no legal way to move anything at the rated max forces for these cylinders. The cylinders can HOLD the max rated force, but they cannot move with that much force. Consider these the stall forces.
Do not forgot the time dimension part of the power equation. Cylinders also have a force versus time curve for each given pressure . My team has done some experiments and have proven that these curves are not linear. I have attached a sample of our experimental results. It is difficult to characterize pneumatics because the entire system affects the available airflow volumes (think of a current limiting analogy from electronics), so these curves are very dependent on your set up. I'm too busy right now to go into any more details but I may do a white paper on the power curves of our pneumatic systems during the off-season.
Don't forget to do a "Save As" on the XL file.