text: Rodless cylinders have no rod, only a relatively long piston.  Cable cylinders retain openings at one or both ends, but pass a flexible cable rather than a rod.  This cable has a smooth plastic jacket for sealing purposes. Of course, a single cable has to be kept in tension.  Other rodless cylinders close off both ends, coupling the piston either magnetically or mechanically to an actuator that runs along the outside of the cylinder.  In the magnetic type, the cylinder is thin-walled and of a non-magnetic material, the cylinder is a powerful magnet, and pulls along a magnetic traveller on the outside.
  In the mechanical type, part of the cylinder extends to the outside through a slot cut down the length of the cylinder.  The slot is then sealed by flexible metal sealing bands on the inside (to prevent gas escape) and outside (to prevent contamination).  The piston itself has two end seals, and between them, camming surfaces to "peel off" the seals ahead of the projecting linkage and to replace them behind.  The interior of the piston, then, is at atmospheric pressure.
  One well-known application of the mechanical type (albeit steam-powered) are the catapults used on many modern aircraft carriers.