A prosthetic system includes a pump mechanism operatively connectable to a prosthetic foot. The pump mechanism has a housing defining first and second ports, a membrane having an outer edge portion secured to the housing, and a fluid chamber with a volume defined between the housing and a first side of the membrane. The fluid chamber is in fluid communication with the first and second ports. A connector is attached to a second side of the membrane opposite the first side. The connector operatively connects the membrane to the prosthetic foot such that when no weight is placed on the prosthetic foot the volume of the fluid chamber is zero or near-zero and when weight of a user is placed on the prosthetic foot the membrane deforms to expand the volume of the fluid chamber.
