A fluid powered rotary actuator having a first member which is pivotally connected to a second member and which is includes at least one toroidal shaped spear or piston which acts within a correspondingly shaped toroidal shaped cylinder to move the first member relative to the second member. Each toroidal shaped spear or piston and cylinder assembly includes seals mounted within a seal carrier and the configuration allows movement of the seals relative to the or each cylinder. This configuration allows the seals to continue to provide a leak resistant hydraulic seal between each toroidal shaped spear or piston and its associated cylinder even in cases where the toroidal shaped spears or pistons deflect relative to their associated cylinders. The cylinders are also mounted to the first or second members in a manner designed to reduce the chance of tensile cracking due to deflection of the cylinders.

The invention relates to an actuating unit for locking a component of a construction machine, in particular a road milling machine or a surface miner, the actuating unit comprising a retaining part 26 for fastening to the construction machine.

Furthermore, the invention relates to a self-propelled construction machine, in particular a road milling machine or a surface miner, comprising at least one actuating unit of this type. The basic principle of the actuating unit according to the invention is the design of the cylinder of a piston/cylinder arrangement as a locking bolt. In the actuating unit according to the invention, a piston 27 is connected to the retaining part 26 and is surrounded by a cylinder 30, with a first cylinder chamber 31 being formed on one side of the piston and a second cylinder chamber 32 being formed on the other side of the piston. A cut-out 33 which extends in the direction of the longitudinal axis of the cylinder and through which the retaining part 26 extends is provided in the cylindrical wall of the cylinder 30. If one of the two cylinder chambers 31, 32 is supplied with a fluid, the cylinder 30 moves to one side or the other, while the retaining part 26 remains stationary. Therefore, the cylinder 30 constitutes a locking bolt, which can be pushed forward or pulled back.