Sprocket gear reduction drive for power swivel assembly

Claim 1

A POWER SWIVEL ASSEMBLY FOR THE ROTARY DRILLING OF DEEP WELLS COMPRISING A TUBULAR SHAFT ADAPTED TO BE DRIVINGLY ENGAGED WITH AND SUPPORT A DRILL STRING OR THE LIKE, A FLUID MOTOR, A TWO-SPEED SPROCKET CHAIN TRANSMISSION UNIT DRIVEN BY SAID MOTOR, MEANS DRIVINGLY CONNECTING SAID TRANSMISSION UNIT TO SAID TUBULAR SHAFT, SAID TRANSMISSION UNIT INCLUDING A CASING AND VERTICALLY ALIGNED POWER INPUT AND POWER OUTPUT SHAFTS EACH EXTENDING FROM THE INTERIOR TO THE EXTERIOR OF SAID CASING, A VERTICAL COUNTER SHAFT JOURNALED IN SAID CASING AND PARALLEL TO SAID INPUT AND OUTPUT SHAFTS, A PAIR OF SPROCKET CHAIN DRIVES OF DIFFERENT SPEED RATIOS CONNECTING SAID COUNTERSHAFT TO SAID OUTPUT SHAFT, MEANS FOR SELECTIVELY RENDERING ONE OF SAID CHAIN DRIVES OPERATIVE WHILE THE OTHER CHAIN DRIVE IS RENDERED INOPERATIVE, MEANS IN SAID CASING DRIVINGLY CONNECTING SAID INPUT SHAFT TO SAID COUNTER SHAFT.