A rodless pneumatic cylinder includes main exhaust ports defined by the open ends (10, 11) of a pair of fixed tubular members (8, 9) that extend, respectively, into the cylinder body (1) from its opposed ends (2, 3). The main piston 14 of the rodless cylinder has an axial bore (18) formed in it in which is slidably mounted a small piston (19) that serves mutually to isolate the working chambers (16, 17) of the cylinder. The bore (18) carries seals (20, 21) adjacent to its opposed ends whereby, during motion of the piston (14), the bore (18) sealingly receives one or other of the tubular members (8, 9) at a pre-determined stage during the motion thereby effectively closing the main exhaust port (10 or 11). During further motion of the piston (14), air can, therefore, exhaust only through a throttled auxiliary exhaust port (12, 13) and such further motion of the piston (14) is thus cushioned.
The arrangement provides for a greater extent of cushioning relative to known arrangements in which the working chambers (16, 17) are mutually isolated by a barrier fixedly secured in the bore (18).