Pump drive head pump assembly with a hydraulic pump circuit for

Abstract

A pump drive head includes a housing, and a main shaft carried on upper and lower bearings disposed in the housing. The main shaft includes an outer torque tube and a liner tube. The outer and liner tubes abut along a first portion of their length and are separated along a second portion of their length forming a double wall with an elongate tubular space in between. A standpipe is coupled at one end to the housing, below the lower bearing, and received by the elongate tubular space an eliminates the need for a lower seal on the main shaft. A hydraulic pump includes a hydraulic pump chamber displosed in the housing and communicating with the main shaft, and first and second gears disposed in the hydraulic pump chamber and the first gear coupled to the main shaft. The second gear intermeshes with the first gear. A suction port is located between the first and second gears and operable when the main shaft is rotated in a reverse direction from the normal pumping direction, during a condition known as backspin. A hydraulic circuit coupled to the suction port provides resistance to the reverse direction of rotation of the main shaft. The hydraulic circuit includes a variable orifice, for adjusting tje desired reverse rotation speed in series with a wax motor actuator for temperature sensitive control of reverse rotation speed.