Abstract: An exemplary pump jack system (10) is operable to cause well liquid to be pumped to the surface by a subsurface well pump (29). The exemplary system includes a driver (42) that is in rotatable connection with a pump/motor (48). The pump/motor is a rotary type variable output positive displacement pump/motor that delivers working liquid at a selectively variable flow rate in closed liquid connection to a motor/pump (38). The exemplary motor/pump includes a rotatable output coupler (40) that is in operative connection with a gearbox (34) which causes the pump jack to undergo reciprocating motion. The motor/pump is a rotary type positive displacement motor/pump that is in closed liquid connection with the pump/motor liquid inlet of the pump motor. The pump/motor is operable to deliver working liquid flow therefrom to drive the motor/pump at a selectively variable speed while the driver operates at a generally constant rotational speed.

Abstract: An exemplary pump jack system (10) is operable to cause well liquid to be pumped to the surface by a subsurface well pump (29). The exemplary system includes a driver (42) that is in rotatable connection with a pump/motor (48). The pump/motor is a rotary type variable output positive displacement pump/motor that delivers working liquid at a selectively variable flow rate in closed liquid connection to a motor/pump (38). The exemplary motor/pump includes a rotatable output coupler (40) that is in operative connection with a gearbox (34) which causes the pump jack to undergo reciprocating motion. The motor/pump is a rotary type positive displacement motor/pump that is in closed liquid connection with the pump/motor liquid inlet of the pump motor. The pump/motor is operable to deliver working liquid flow therefrom to drive the motor/pump at a selectively variable speed while the driver operates at a generally constant rotational speed.

Abstract: A fluid balanced hydraulic pump has a support tower that can be mounted over a well. At least one cylinder assembly is pivotally mounted within the support tower. A prime mover provides hydraulic fluid to the at least one cylinder assembly through a wedge spool control valve that provides precise speed control with minimal maintenance requirements. Stroke speed can be easily and quickly adjusted without the need for expensive, troublesome or complicated electronic equipment.

Abstract: A fluid balanced hydraulic pump has a support tower that can be mounted over a well. At least one cylinder assembly is pivotally mounted within the support tower. A prime mover provides hydraulic fluid to the at least one cylinder assembly through a wedge spool control valve that provides precise speed control with minimal maintenance requirements. Stroke speed can be easily and quickly adjusted without the need for expensive, troublesome or complicated electronic equipment.