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Typically, air cylinders are linear devices. They are designed to transmit force down the axis of the piston rod. In order to use the air cylinder it’s necessary to attach some sort of tooling to the end of the rod, and it’s this attachment that is often the source of the problem.
As a typical double-acting air cylinder operates, compressed air alternately extends and then retracts the rod, by moving the piston from end to end inside the barrel of the cylinder.
When the cylinder is in a retracted position - with minimal extension - any tangential force on the rod tip or rod end tooling, can be more easily absorbed by first; the rod bearing which is what the rod passes through as it exits the end cap of the cylinder, and then by piston itself, being forced sideways against the inner surface of the air cylinder barrel as pressure is applied sideways against the tip of the rod. The distance between the two bearing points, the rod bearing and the piston itself, ameliorates the side load.
Consider how the ability of the cylinder to withstand sideloading changes as the rod extends. Now the rod bearing and the piston are very near to each other, and since the piston cannot provide the same support, more of the tangential load is taken up by the seals and the actual rod bearing itself.
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Sideloading of the cylinder rod is a very common cause of failure of an air cylinder or air actuator through leakage at the rod seals, scoring and leaking of the inside of the cylinder barrel, or the inability of the cylinder to overcome the additional friction imposed by the side load.
Where the rod tip or rod-end tooling might see tangential force, you can use larger rod bearings, have a stop collar installed inside the cylinder barrel to ensure that the piston can't reach the rod end of the cylinder - thus effectively increasing the bearing area, or by guiding the load in such a fashion that sideloading is absorbed by the guiding mechanism, and any force from the side is not applied to the cylinder rod at all.
An alignment coupler is a device that connects the end of the rod to the tooling, and can itself adjust to reduce side load as the rod cycles.
Clevis mounts on the rod end connecting to a mating clevis in the tooling will allow some movement of the tooling without side loading the cylinder rod.
Here's more info on compressors in general sideloading.
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