A vacuum pump (102, 202, 300, 600, 900, 1000, 1100, 1200, 1300) for a prosthetic device, comprising: a housing (302, 604, 902, 1004, 1102) having an inner wall (318, 918); a piston (214, 228, 334, 606, 934, 1006, 1116, 1212) having an outer diameter (342, 942) and being secured within the housing (302, 604,902,1004, 1102); a shaft (304, 332, 602, 904, 1002, 1104) having an inner surface and being positioned between the inner wall (318, 918) of the housing (302, 604, 902, 1004, 1102) and the outer diameter (342, 942) of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212); an upper fluid chamber (208, 336, 936) positioned between a top surface of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the inner surface of the shaft (304, 332, 602, 904, 1002, 1104), the upper fluid chamber (208, 336, 936) having a variable volume as the shaft (304, 332, 602, 904, 1002, 1104) moves axially in relation to the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the housing (302, 604, 902, 1004, 1102), the upper fluid chamber (208, 336, 936) being fluidly connectable to a socket (108, 301) of the prosthetic device through a first valve and fluidly connected to atmosphere through a second valve and that a lower fluid chamber (210, 338, 938) being fluidly connectable to the socket (108, 301) through a third valve and fluidly connected to atmosphere through a fourth valve, characterized in that the lower fluid chamber (210, 338, 938) is positioned between a bottom surface of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the inner surface of the shaft (304, 332, 602, 904, 1002, 1104), the lower fluid chamber (210, 338, 938) having a variable volume as the shaft (304, 332, 602, 904, 1002, 1104) moves axially in relation to the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the housing (302, 604, 902, 1004, 1102). a housing (302, 604, 902, 1004, 1102) having an inner wall (318, 918); a piston (214, 228, 334, 606, 934, 1006, 1116, 1212) having an outer diameter (342, 942) and being secured within the housing (302, 604,902,1004, 1102); a shaft (304, 332, 602, 904, 1002, 1104) having an inner surface and being positioned between the inner wall (318, 918) of the housing (302, 604, 902, 1004, 1102) and the outer diameter (342, 942) of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212); an upper fluid chamber (208, 336, 936) positioned between a top surface of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the inner surface of the shaft (304, 332, 602, 904, 1002, 1104), the upper fluid chamber (208, 336, 936) having a variable volume as the shaft (304, 332, 602, 904, 1002, 1104) moves axially in relation to the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the housing (302, 604, 902, 1004, 1102), the upper fluid chamber (208, 336, 936) being fluidly connectable to a socket (108, 301) of the prosthetic device through a first valve and fluidly connected to atmosphere through a second valve and that a lower fluid chamber (210, 338, 938) being fluidly connectable to the socket (108, 301) through a third valve and fluidly connected to atmosphere through a fourth valve, characterized in that the lower fluid chamber (210, 338, 938) is positioned between a bottom surface of the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the inner surface of the shaft (304, 332, 602, 904, 1002, 1104), the lower fluid chamber (210, 338, 938) having a variable volume as the shaft (304, 332, 602, 904, 1002, 1104) moves axially in relation to the piston (214, 228, 334, 606, 934, 1006, 1116, 1212) and the housing (302, 604, 902, 1004, 1102).