Patent ID: 6113355
Filing Date: 2000-09-05
Classification: E21B,F04C

Abstract:
A pump drive head comprising:a housing;a main shaft comprising an outer tube and a liner tube, rotatably supported in the housing and connected to a pump driving rod, wherein the outer and liner tubes abut along a portion of their length and are separated along another portion of their length thereby forming an elongate tubular space;a driving apparatus operatively connected to the main shaft;a hydraulic pump operatively connected directly or indirectly to the main shaft;a hydraulic circuit connected to the hydraulic pump, the hydraulic pump having a first and a second direction of operation, the first direction pumping little or no fluid through the hydraulic circuit, thereby providing a relatively low resistance to rotation of the main shaft, the second direction pumping fluid through the hydraulic circuit, thereby providing a relatively high resistance to rotation of the main shaft; anda standpipe coupled at one end to the housing, below the lower bearing, and received within the elongate tubular space between the outer and liner tubes of the main shaft.