Abstract: A positive displacement pump (1) for transporting a fluid with automatic adaptation to the compressibility of that fluid has a pumping chamber (15) with a variable volume (V) which is on the one hand delimited by a rigid chamber cover plate (10) and on the other hand by an elastic diaphragm (9), a suction channel (29) which is in flow connection with the pumping chamber (15) for sucking the fluid to be transported into the pumping chamber (15), an outlet channel (24) which is in flow connection with the pumping chamber (15) for discharging the fluid to be transported from the pumping chamber (15), and a drive device (29) for cyclically increasing and reducing the current volume (V) of the pumping chamber (15), with the drive device (29) being connected to the diaphragm (9) by means of a diaphragm connecting element (34; 34a; 34b) which is spring-mounted in the drive device (29) by means of a spring element (33; 33a; 33b).