A method and system is intended for fine proportioning of fluids injected into
a pumping installation, e.g., a liquid chromatography installation, allowing to
compensate for non-return valve errors. The system includes a fluid delivery system
including vessels for constituents (A, B, X) that communicate with a pumping unit
(1-11) by means of a one-way valve (8) that opens upon suction, and
a control unit (PC) that adjusts the respective proportions of the various fluids
sucked by acting on the opening time of solenoid valves (EV1 to Even) associated
with the various vessels. As the opening and closing times of the one-way valve
are most often unequal in practice, control unit (PC) is suited to cyclically change
the order of the control signals applied to the various solenoid valves during
the various successive suction stages of each pumping unit so as to compensate
on average for the proportioning inequalities due to each one-way valve.