A hydraulic pump assembly 72 comprises a low pressure hydraulic pump 74, a high pressure hydraulic pump 76, and a drive shaft assembly 78 that passes along an axis of the pump assembly 72； wherein both hydraulic pumps 74, 76 are arranged to be rotated simultaneously by the same drive shaft assembly 78； and wherein the pump assembly 72 is formed as a single unit arranged to fit into a pump chamber 80. The pump chamber may be cylindrical, and the drive shaft may pass through one pump to reach the other. The pumps may be gear pumps. The drive shaft may be rotated by a motor 68 via belt 28 (see figure 5). The pump assembly may for part of a palm unit for an artificial or prosthetic hand.
