Importance

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Abstract

A horizontal directional drilling machine includes a drill string rotational drive unit having an output member configured to connect with and selectively drive rotation of a drill string, the rotational drive unit including a hydraulic motor. A hydraulic circuit has a configuration that puts the motor in a drive mode to apply torque and a second configuration that puts the motor in a freewheel mode disabled from applying torque. The hydraulic circuit includes a first fluid flow path for connecting the hydraulic motor through a first rotary ball valve to one of an inlet side and an outlet side of a drive pump, and a second fluid flow path for selectively connecting the hydraulic motor through a second rotary ball valve to the other side of the drive pump. In the first configuration, there is no pressure drop across the first and second rotary ball valves.

First Claim