A few guidelines for figuring pneumatic-actuator load requirements

Cylinders are rather simple devices, and calculating the theoretical force output is fairly straightforward. But sizing a cylinder for a specific application can be a more challenging task. Undersizing, for instance, is a common mistake. However, by following a few simple guidelines, engineers and technicians can quickly determine the right cylinder to fit a specific need. The theoretical force output of a cylinder is the usable piston area multiplied by the applied air pressure ( ). For example, a cylinder with a 1 -in. bore and an extend force of 80 psi generates 141 lb of force (1.767 × 80 = 141). This is the theoretical force output, but there are several factors that lower the actual output force. Keep the following issues in mind when sizing a cylinder. Subtract the rod area, if applicable. The theoretical force output is the usable piston area multiplied by air pressure. If using the return stroke, or a double-rod cylinder, then subtract the rod area to calculate the usable piston area. Know the actual operating pressure. Although a compressor is rated for a certain pressure, the pressure that the cylinder actually sees in operation can be much lower due to factors such as other equipment's air consumption or other air-supply restrictions. An air system that runs at 100 psi may drop to 80 psi or lower during peak air usage times. Because of internal friction, cylinders never reach their theoretical force output. Seals, bushings, wear bands and other load-support items all produce internal friction. The force loss is typically 1 to 10 psi of theoretical force output of the cylinder, depending on the type of seal. Cylinders with side loads, misalignment, or specialty features have even higher internal friction. Remember that cylinders convert pressure to linear force. Considerable side loads and bending moments should