Pneumatic cylinders

You need four values: bore, stroke, port thread and mounting style. Bore is the inside diameter of the barrel or can be inferred from the rod diameter using the maker's table, and stroke is the rod travel from fully retracted. Also check the rod end thread and whether the cylinder has a magnet for sensors.

ISO 6432 covers small round cylinders with bores of 8 to 25 mm. ISO 15552 covers profile or tie-rod cylinders with bores of 32 to 320 mm. Both fix the mounting dimensions and rod thread, so cylinders to the same standard from different makers are usually mechanically interchangeable.

Theoretical push force equals pressure times piston area: a 50 mm bore at 0.5 MPa gives about 980 N. The pull stroke is lower because the rod area is subtracted. Size the real load at roughly 50 to 70 percent of theoretical force to allow for friction and pressure drop.

In SMC codes the prefix is the series (CJ1 is a miniature round cylinder), the next letter is the mounting, then the bore, then the stroke after the hyphen. Trailing characters are options such as thread type or accessories. The structure varies by series, so always check that series' catalogue rather than guessing.

Usually the speed is too high for the cushioning, or the cushion screw is fully open. Fitting meter-out speed controllers and resetting the air cushion solves most cases. Heavy loads at high speed may need an external hydraulic shock absorber.

Inspect the piston rod regularly for scoring, rust or bending, because a damaged rod surface destroys seals quickly. Listen for hissing at the end caps and rod gland to catch worn seals early. Replacement seal kits are usually available by cylinder model, so the unit can be repaired rather than replaced.

The common method is a one-way flow control at the cylinder port restricting exhaust air (meter-out), which gives smoother, steadier motion than restricting supply air. To make a cylinder faster, use larger tubing and valves or fit a quick exhaust valve close to the port. Single-acting or very small cylinders sometimes need meter-in control instead.

Pneumatic cylinders are designed for axial force, and side load on the rod wears the guide bushing and rod seal unevenly. Use a floating joint to absorb misalignment between the rod and the load. Where the load needs guiding, use a linear guide or a guided cylinder rather than letting the rod carry it.