A pump of extremely simple manufacture, requiring no maintenance, is made up of a tubular body (1) closed at each end by end pieces (10a and 10b), orifices (15a and 15b) of which are respectively connected to a pneumatic control circuit (4) and to the circuit of liquid in circulation (3). A piston (2) circulates freely within the tubular body, driven by an overpressure or an underpressure appearing in the upper chamber (17a) and controlled by the pneumatic control circuit. The displacement of the piston brings about the filling and emptying of the lower chamber (17b), thus permitting the pumping of a liquid. This type of pump, of universal use, needs only a connection to a compressor (40) and to a vacuum pump (41) for its running, and these two elements may be common to a great number of such pumps.