A top drive is a mechanical device on a that provides clockwise torque to the to drill a . It is an alternative to the and . It is located at the place below the traveling block and moves vertically up and down the derrick. [pdf]
The twin-screw type supercharger is a type device that operates by pushing air through a pair of meshing close-tolerance screws similar to a set of worm gears. Twin-screw superchargers are also known as Lysholm superchargers (or ) after their inventor, . Each rotor is radially symmetrical, but laterally asymmetric. By comparison, convent. [pdf]
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