The invention relates to pressure generating units, in particular to pressure generating unit arranged in the hand piece of a vacuum biopsy device in the form of a singe (2). In said units, air intake is open by a piston when said piston (5) is in the rear position thereof in the space of a vacuumed cylinder (11) which is switched for generating a superpressure, thereby initiating the outflow of a tissue liquid by the air introduced into the space of the vacuumed cylinder. For this purpose, the space of the vacuumed cylinder is connected to the space of an atmosphere pressure cylinder (12) arranged behind the piston, by means of a connection line (15), and an absorbing element (14) is placed on the piston axis.