An electro-hydraulic piston pump system comprising an electric motor (16), first and second hydraulic piston pumps (30,60), a first hydraulic actuator (90) having a first port (93) connected directly to a first port (48) of the first pump and a second port (94) connected directly to a second port (49) of the first pump, a second hydraulic actuator (100) having a third port (103) connected directly to a third port (78) of the second pump and a fourth port (104) connected directly to a fourth port (79) of the second piston pump, wherein an external force applied to the first hydraulic actuator (90) that provides a negative pressure differential to the first pump applies an assistive torque to a common motor shaft (18) driving both the first pump (30) and the second pump (60), and an external force applied to the first and second actuators (90,100) that provides a summed negative pressure differential to the first and second pumps (30,60) recharges a power supply for the motor (16).

An electro-hydraulic piston pump system comprising an electric motor (16), first and second hydraulic piston pumps (30,60), a first hydraulic actuator (90) having a first port (93) connected directly to a first port (48) of the first pump and a second port (94) connected directly to a second port (49) of the first pump, a second hydraulic actuator (100) having a third port (103) connected directly to a third port (78) of the second pump and a fourth port (104) connected directly to a fourth port (79) of the second piston pump, wherein an external force applied to the first hydraulic actuator (90) that provides a negative pressure differential to the first pump applies an assistive torque to a common motor shaft (18) driving both the first pump (30) and the second pump (60), and an external force applied to the first and second actuators (90,100) that provides a summed negative pressure differential to the first and second pumps (30,60) recharges a power supply for the motor (16).

A piston unit includes a piston which has a rolling element seat configured to rotatably support a rolling element. The rolling element seat has a bearing surface with a surface coating composed of a polymer compound or with a ceramic surface coating.