Abstract: A dual drill string actuator includes a piston disposed in a housing. The housing is configured to sealingly couple at its longitudinal ends to an end of a nested dual drill string segment. An upper internal conduit is mounted in the housing proximate one longitudinal end thereof. A lower internal conduit is mounted in the housing proximate the other longitudinal end thereof. The piston is slidably, sealingly engaged between the upper and lower inner conduits and together define an internal fluid flow passage therethrough. The upper inner conduit, the piston and the lower inner conduit also define an external flow passage between respective exterior surfaces thereof and an interior of the housing such that application of fluid pressure to the external flow passage causes movement of the piston.