Apparatus for transferring a reciprocating movement from a surface machinery to a downhole device and a method of producing well fluids

Method of producing a wellbore fluid utilizing an apparatus, the apparatus comprises a longitudinal hollow body, an upper rod connected to a machinery in one end thereof and to an upper displacement body in an opposite end, a lower displacement body adapted to operate a device, wherein the apparatus further comprises a hydraulic tube, which hydraulic tube in one end thereof is connected to the longitudinal hollow body and in another end is connected to a hydraulic monitoring and pressure adjustment unit, and wherein the pressure in the liquid can be monitored and adjusted by the hydraulic monitoring and pressure adjustment unit,

• wherein the method comprises the following steps:
• operating the machinery arranged at the surface to cyclically move the upper rod to reciprocate relative the longitudinal hollow body,
• transferring the reciprocating movement of the upper rod to a reciprocating movement of a liquid in the longitudinal hollow body,
• transferring the reciprocating movement of the liquid to the lower displacement body and thus the device, wherein the upper displacement body, the lower displacement body and the liquid are configured to reciprocate synchronously relative to the longitudinal hollow body.