The present invention is related to a vacuum unit that can suck in the air inside the carrier shell and which can be used as ankles of prosthetic legs. The present invention aims to develop a vacuum unit which enables the suction of air trapped between the stump and the socket of the prosthesis used by the users or patients who are using lower knee or upper knee prosthesis. Another aim of the invention is to provide vacuum without the need to use electrical energy by mechanically driving the piston which enables vacuum. Another aim of the invention besides these is to ensure that there is no need for a different/special motion by means of the triggering the piston motion within the vacuum medium via the force obtained from natural walking motions.