A palm unit for an artificial hand comprises a palm unit body 70； a motor 68； a hydraulic pump assembly 72 comprising a low-pressure hydraulic pump 76 and a high-pressure hydraulic pump 74, both powered simultaneously by the motor 68； and a hydraulic circuit coupled to both hydraulic pumps 74, 76, wherein the hydraulic circuit has a low-pressure configuration in which the discharge sides of both hydraulic pumps 74, 76 are coupled to one or more hydraulic actuator(s) 36, 38 for the artificial hand, and a high-pressure configuration in which the discharge side of the low-pressure pump 76 is isolated from the hydraulic actuator(s) 36, 38 and recirculates fluid to the suction side of the low pressure pump 76, with the discharge side of the high-pressure pump 74 remaining coupled to the hydraulic actuator(s) 36, 38. The hydraulic circuit is arranged to switch from the low-pressure configuration to the high-pressure configuration automatically during a closing grip pattern when the system pressure increases beyond a threshold value.
