Abstract: Apparatus for generating linear motion comprises a body on one end of which is mounted a cylinder. A piston in the cylinder is joined to an actuating beam extending into the body. The actuating beam has moving surfaces that cooperate with fixed surfaces in the body to define a linear bearing. Fluid under pressure is introduced through a duct in the body to a port in the fixed surface of the linear bearing. It enters the space in the cylinder above the piston via a port in a moving surface of the actuating beam which leads to a duct in the actuating beam that opens through the crown of the piston. A resilient sealing member between the fixed and moving surface of the linear bearing maintains fluid-tight communication between the fixed and movable part over their range of relative movement. The actuating beam may carry a rack that drives a pinion through ninety degrees as the piston travels, and two opposed cylinders may be provided to give a reciprocatory movement, or a spring return may be provided.