Abstract: An apparatus for feeding fluid-flow substances composed of at least two mutually reacting components, in particular casting resin, the components being fed from piston-cylinder units (7, 8) associated with supply vessels (1, 2) and from there being conveyed to a mixing system (36). The piston-cylinder units (7, 8) are fitted with retraction capability for the conveyor pistons (17, 19). A drive system is provided to load the conveyor pistons (17, 19) with a pressurized fluid. The piston-cylinder units (17, 19) evince a displacement volume of which the lower limit is determined by the viscosity of the component to be conveyed and the stroke frequency of the conveyor pistons (17, 19) in relation to the required rate of conveyance. The displacement volume of the piston-cylinder units (7, 8) may be between 0.1 and 4 ltr, preferably being 1 ltr.