Hydraulic actuator having frangible or deformable components

Abstract

A linear hydraulic actuator of small size having limited clearance between the inside of the cylindrical housing and the outside of the piston rod is provided with a deformable or frangible piston of an engineered plastic material which is sufficiently strong to survive normal operation of the actuator but which will break or deform if the cylinder is punched through or 'petalled' causing inward projections tending to block movement of the piston. Another embodiment discloses a plastic end gland which is frangible, or deformable in the event of an impact deforming the rod such that it would not pass through the end gland except for such deformation. Because of the relative weakness of the plastic material, the width of the land on the piston acting against the inside of the cylinder is maximized by placing the dynamic seals at or near its outside circumferential edges. Similarly, the internal surface of the plastic end gland also has a dynamic seal at an outer edge to maximize the width of the surface against which the piston rod moves. In either case, fragments of the plastic members are not of such strength as to block movement of the rod when it is being moved by another undamaged actuator.