Down-hole devices for imparting rotary motion

Claim 1

A down-hole device for converting the kinetic energy of the mud flow passing along a drill string into rotary motion for driving a generator or a measuring or signalling instrument, the device comprising a rotary drive member arranged to have its rotational axis disposed along the axis of the drill string, an annular bladed impeller coaxial with the drive member to which it is operatively coupled to impart driving torque thereto and having a plurality of radially outwardly projecting blades distributed about the circumference thereof and arranged to be driven by the mud flow, an annular impeller bearing, and an annular bladed stator coaxial with the drive member and having a plurality of radially outwardly projecting blades distributed about the circumference thereof and arranged immediately upstream of the impeller so as to act on the mud flow before it reaches the impeller, the blades of the stator being canted relative to the mud flow and relative to the blades of the impeller to cause the mud flow to impact on the blades of the impeller at such an angle that a small or negligible thrust results at the impeller bearing due to the combined effect of the mud flow acting on all the blades of the impeller.