Abstract: An isolator which includes an isolator shaft, an isolator closure, e.g., a valve plate, carried by the isolator shaft, a hydraulic actuator for the isolator shaft, an auxiliary shaft equipped with at least one element for driving at least one extraneous device, e.g., a limit switch, and a coupling drivingly interconnecting the isolator shaft with the auxiliary shaft. The hydraulic actuator includes a casing which has an exterior mounting flange at one end for connection to the isolator and internally houses a hydraulic ram and a lever arm assembly, with the ram being articulated at one end to the lever arm assembly and at the other end to the end of the casing remote from the flange.