A hydraulically-driven vacuum pump is used for a prosthetic or orthotic artificial limb for amputees having a residual limb. The artificial limb has a pylon and a socket for receiving the residual limb. The vacuum pump is connected to the socket and mounted in-line on the pylon. An upper portion housing of the vacuum pump is connected to the vacuum pump by a port. A lower portion housing of the vacuum pump reciprocates within the upper housing portion and is connected to a piston of the hydraulic pump. The weight of the amputee bears on the pylon and drives the lower portion within the upper portion thereby driving the hydraulic pump.