Oscillating fluid-driven actuator

In an oscillating fluid-driven actuator for a driving shaft, of the kind having

• i. an actuator housing comprising upper and lower housing members having an internal face defining an annular segment-shaped chamber substantially coaxial with the shaft
• ii. an annular segment-shaped piston arranged coaxially with the shaft in the chamber and fixedly connected to the shaft by a central hub having an axis of rotation, and
• iii. an arm extending between the hub and the annular piston at a point of said annular piston intermediate its ends, the peripheral extent of the piston being less than 360.degree., the improvement in which, in combination:
• a. said hub of said annular segment-shaped piston has a spherical convex bearing surface which is opposed to and in sliding contact with a corresponding concave spherical bearing surface in said actuator housing, said convex bearing surface and said concave bearing surface both having their centre lying on the axis of rotation of the hub,
• b. said piston includes an annular segment-shaped piston body spaced from said internal face of said housing
• c. said piston includes a respective sealing head at each circumferential end of said piston body and in sealing engagement with said internal face and slidable along said internal face,
• d. said piston includes respective means mounting each sealing head on an end of said piston body, said mounting means being constructed to permit movement of the sealing head within limits relative to the piston in a respective radial plane containing the axis of the hub, said upper housing member having a central top opening, and wherein there is provided a cover covering said top opening, and an upper housing bearing surface being provided on said cover cooperating directly with said hub whereby movements of said shaft and piston, out of coaxiality with said housing, can take place by relative movement between said piston body and sealing heads.