US Patent 10072487 Lift apparatus for driving a downhole reciprocating pump

A lift apparatus and method for driving a downhole reciprocating pump is disclosed. The apparatus includes a hydraulic cylinder having a piston and a hydraulic fluid port, the piston being coupled to a rod for driving the reciprocating pump, the piston being moveable between first and second ends of the cylinder in response to a flow of hydraulic fluid through the hydraulic fluid port. The apparatus also includes a variable displacement hydraulic pump coupled to receive a substantially constant rotational drive from a prime mover for operating the hydraulic pump, the hydraulic pump having an outlet and being responsive to a displacement control signal to draw hydraulic fluid from a reservoir and to produce a controlled flow of hydraulic fluid at the outlet. The apparatus also includes a hydraulic fluid line connected to deliver hydraulic fluid from the outlet of the hydraulic pump through the hydraulic fluid port to the cylinder for causing the piston to move through an upstroke away from the first end and toward the second end of the cylinder. The apparatus further includes a valve connected between the hydraulic fluid port and the reservoir, the valve being responsive to a valve control signal for controlling discharge of hydraulic fluid from the hydraulic fluid port of the cylinder back to the reservoir to facilitate movement of the piston through a downstroke away from the second end toward the first end of the cylinder. The valve is operable to prevent flow of hydraulic fluid through the valve during the upstroke and the hydraulic pump is operable to prevent flow of hydraulic fluid back into the outlet of the hydraulic pump during the downstroke.