Magnetically coupled cylinders are air cylinders designed to fill a specific need!
Unlike other types of rodless air cylinders such as band cylinders or cable cylinders which have the cylinder carriage mechanically attached to the piston, there is no mechanical connection between the carriage and the piston inside a magnetically coupled air cylinder barrel.
Instead, a magnetically coupled, rodless air cylinder will have a strong rare-earth magnet as part of the cylinder piston. Another similar high-strength magnet will be part of the cylinder carriage. The attraction between these two magnets is what allows the carriage to be propelled along outside the cylinder barrel by the compressed air driven piston inside the cylinder barrel.
In the drawing above I focus on the piston inside the cylinder barrel, conceptualizing the magnet built in as part of the piston assembly.
Each manufacturer of magnetically coupled air cylinders will have their own design, of course, the drawing is to show concept, not engineering details.
The sketch below shows the carriage on the cylinder to the left, and then an end view of the carriage, with the magnet as part of the carriage itself.
It is necessary to select the cylinder that provides the coupling force between the carriage and piston that suits the mass of the load and the speed that the mass is desired to be moved.
Different styles offer variations on plumbing, with air ports in the end or on the sides of the end caps.
Make careful note of how you want to install the magnetically coupled cylinder in your application. That detail might determine the manufacturer of the mounting style you need.