Hydraulic actuator with mechanical piston position feedback

A downhole pump system comprising:

• a piston rod pump assembly;
• and
• a hydraulic actuator coupled to said piston rod pump assembly, said hydraulic actuator comprising:
• a piston housing having a head end and a base end opposite said head end;
• a drive piston disposed within said piston housing and movable between a first piston position proximate to said head end and a second piston position proximate to said base end;
• a control valve positionable between a first control valve position and a second control valve position, wherein:
• in the first control valve position, said control valve is configured to direct fluid into said base end;
• and
• in the second control valve position, said control valve is configured to direct fluid into said head end;
• and
• a mechanical position feedback system configured to:
• translate said control valve from the first control valve position to the second control valve position in response to said drive piston moving to the first piston position;
• and
• translate said control valve from the second control valve position to the first control valve position in response to said drive piston moving to the second piston position.

A method of controlling a hydraulic actuator, the hydraulic actuator including a piston housing having a head end and a base end opposite the head end, a drive piston disposed within the piston housing and movable between a first piston position proximate to the head end and a second piston position proximate to the base end, and a control valve positionable between a first control valve position and a second control valve position, said method comprising:

• determining, using a mechanical position feedback system, that the drive piston has moved into the second piston position;
• transitioning, in response to determining that the drive piston has moved into the second piston position, the control valve from the second control valve position to the first control valve position, wherein in the first control valve position, the control valve directs fluid into the base end of the piston housing;
• determining, using the mechanical position feedback system, that the drive piston has moved into the first piston position;
• and
• transitioning, in response to determining that the drive piston has moved into the first piston position, the control valve from the first control valve position to the second control valve position, wherein in the second control valve position, the control valve directs fluid into the head end of the piston housing.