Patent ID: 7318489

Claim:
A hydraulic motor arrangement comprising a hydraulic motor and supply means for supplying a drive liquid to the hydraulic motor for driving the hydraulic motor, which supply means comprises a first and a second expel reservoir, whereby the first expel reservoir is arranged to hold the drive liquid, and arranged to receive a pressurized working fluid different from the drive liquid from a high-pressure zone, and upon receipt thereof to displace and expel the drive liquid from the first expel reservoir into an expel system which includes the hydraulic motor, and whereby the second expel reservoir is arranged downstream the hydraulic motor to receive the expelled drive liquid and, upon receipt thereof, to displace and expel an exhaust fluid different from the drive liquid into a low-pressure zone, wherein the hydraulic motor arrangement is installed in a drill string, the drill string forming a conduit, wherein the high pressure zone is inside the drill string and the low pressure zone is outside the drill string.