While a leaking pneumatic cylinder does not represent the environmental and safety catastrophe that a leaking hydraulic cylinder does, it’s still a serious situation that you should pay attention to. In addition to the fact that air leakage means wasted energy, it’s also a sign that either the system was designed improperly (say, with high side loads that are damaging the cylinder upon extension), or more likely, that the cylinder is nearing the end of its useful life and has to be replaced.
An air cylinder will generally leak the most at the shaft, at the point where the rod moves in and out—the location of the rod seal. Some technicians recommend putting a small amount of soapy solution (bubbles) in this area to better see if this is the source of the leak. Other areas include welded seams or at the air connection points—where the air lines enter the cylinder body.
Air cylinders generally leak because their seals have worn out, sometimes exacerbated by internal rusting of the metal components. If a piston or rod seal is the culprit, these can be replaced, and seal kits are widely available. Some cylinders are the non-repairable type, and if this is what you are dealing with, the entire cylinder will have to be replaced.
