A fluid supply system configured for metering two or more fluids in controlled proportions, including a plurality of solvent supply lines, a pumping unit configured for taking in fluids from selected solvent supply lines and for supplying a pressurized mixture, a proportioning valve configured for modulating solvent composition by sequentially coupling selected ones of the solvent supply lines with the inlet of the pumping unit, a sensor configured for sensing process information in the fluid supply system, an analysis entity configured for analyzing the process information for determining reciprocating element related information at a beginning of fluid intake, and a control unit configured for switching the proportioning valve to sequentially couple selected ones of the solvent supply lines to the inlet of the pumping unit at one or more switching points based on the given metering scheme and based on the reciprocating element related information.