Linear actuator

A linear hydraulic actuator comprising a hollow main piston axially moveable, through a range of movement, between a rest position and an actuated position, in an elongate cylinder under the influence of hydraulic pressure, the main piston defining a bore within which a seal member is provided, the seal member forming a sliding seal with the bore of the main piston wherein the seal member comprises a supplementary piston slidably received within said main piston and movable longitudinally relative to said cylinder between a rest position and a limit position, said supplementary piston and said main piston including respective abutment surfaces which co-act when both the main piston and the supplementary piston are in their respective rest positions and hydraulic pressure is applied to said supplementary piston to move it from its rest position towards its limit position, the abutment of said surfaces of said supplementary piston and said main piston being such that during movement of the supplementary piston from its rest position towards its limit position said supplementary piston pushes the main piston in its movement from its rest position towards its actuated position.