The invention relates to an apparatus for transferring a reciprocating movement from a machinery arranged at a surface to a device located downhole in a subterranean well, the apparatus comprising: a longitudinal hollow body an upper rod connected to the machinery in one end thereof and to an upper displacement body in another end thereof, a lower displacement body adapted to operate the device, the upper displacement body and the lower displacement body are in communication via a liquid in the longitudinal hollow body, and are movable within the longitudinal hollow body, and wherein the upper displacement body, the lower displacement body and the liquid are configured to reciprocate synchronously relative to the longitudinal hollow body. The invention further relates to a method of producing a wellbore fluid.