The unit (10) has a piston (80) comprising a drive body (81) and a sealing body (100) that is designed as a disk made from rubber or silicone material. The drive body made from fluorinated hydrocarbon has a body with an elastic blanket arranged at an inner wall of a cylinder (20). Cylinder chamber areas are connected with one another over a valve. The drive body is arranged in the cylinder behind the sealing body. The sealing body is completely accommodated by the drive body during forward driving such that the combination of the drive and sealing bodies has the function of the piston.
