A lifting mechanism comprises a mounting structure (12) and an arm (8) attached to the mounting structure through a pivot (10). The arm (8) is arranged for movement about the pivot between a first position and a second position. The mechanism further includes a hydraulic drive means (14) for rotating the arm (8) about the pivot and a hydraulic circuit for supplying drive fluid to the hydraulic drive means, said hydraulic circuit including a valve (20) for controlling the flow of hydraulic fluid through the circuit. The valve (20) has a first operational condition in which flow is permitted and a second operational condition in which flow is prevented. An actuator (24) for actuating the valve (20) is constructed and arranged to move the valve from the first operational condition to the second operational condition when the arm (8) moves from the first position to the second position.
