That depends on a number of factors such as:

Load – what is the weight or mass as determined by pounds or kilograms?

Friction – how much resistance? Smooth surface or rough?

Speed – how many inches per second will the load be traveling?

In general, the air cylinder bore should generate at least 25% more force than the load you plan to overcome.  For higher speed applications, over-sizing the bore by more than 50% greater than the total needed to overcome the load is required.

Example: Your load needs to travel 12” in one second.  The load is on a platform that you plan to lift 12 inches.  The total weight of the platform and the load is 65 pounds. The platform    is well guided with little resistance or drag

To overpower the load by 25% as a minimum, you will need a cylinder capable of providing approximately 82 pounds of output force.  A 1-1/8” bore cylinder operating at 82 PSI, will produce approximately 82 pounds of output force.  If it requires high-speed travel (such as 6 or more inches per second) it is advisable to over size the load by a minimum of 50% and or even double.  Over-powering by 50% would require the same 1-1/8” bore cylinder to be operated by 98 PSI air pressure or higher.  Since most plant compressed air systems tend to supply less than 90 PSI, then the wiser alternative would be to move up in bore size.  A 1-1/4” bore cylinder operating at 80 PSI will deliver 98 pounds of output force.

NOTE:  This is the force generated on the “blind” end or NON-rod side of the piston.  The output force on the ROD end side of the piston is reduced due to the loss of the annular area of the piston rod, itself.

You can short-cut the sizing process by using a “Force Factor” matrix offered by many of the cylinder manufacturers.  For a quick reference, click here, to see the Clippard Force Factor Chart found on pages 3 through 7 of their Complete Products Catalog.  This easy to use chart helps identify the force generated on the “extend” side of the piston versus the retract side.

You’ll find other useful information in these pages such as the maximum load recommended to avoid “buckling” of a cylinder rod based on its diameter, information on “cushioning” your cylinder load, and various spring recommendations for single acting air cylinders.

And as always, please don’t hesitate to contact Isaacs Fluid Power Equipment Company to assist you in your application or selection process, and of course, to place your order.