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This is the measure of pressure. Pressure is the amount of force exerted in a specific unit of area; in the case of compressed air, a single square inch.
When you have an application that requires a certain amount of compressed-air generated force, perhaps to lift a certain weight, you will need to flow compressed air into an actuator at sufficient pressure so that the compressed air, acting on the surface area of the piston inside that actuator, generates enough force to lift the load.
If the load that you are trying to lift is 100 lbs., and the surface area of your piston inside your actuator is 1 sq/in in size, then your compressed air pressure would need to be at 100 Pounds Per Square Inch to give you the theoretical lift force you would need for the application.
We say theoretical, as force is also consumed by friction caused within the actuator itself (seals against rod and piston) and friction caused by whatever the rod-end load may be sliding on or against; all of which adds to a greater-than-theoretical actual force requirements for your ‘real world’ application.
You will always need more force to be available from your actuator than the actual load you wish to move may suggest. You can, and you should, ‘design in’ a wide margin of safety by over-sizing your actuator.
If you needed 100 lbs. of lift, and you expected that your air supply would be at a constant 100 PSI., rather than having a 1 sq/in sized piston in the cylinder, you might consider using one with a 2 sq/in piston.
By moving up in actuator size, you’ve allowed for significant additional force to be available to handle the increased load due to friction.
Also, if your available air pressure should be reduced by consumption elsewhere in your plant, building in over capacity in a cylinder application means that you might still have enough air pressure left at that location to lift your load.
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