Abstract: A pneumatically operated metering pump having in a single cylinder, a driven piston and a slave piston that operates as a sliding valve for admitting fluid into the pump and drawing it into the cylinder between the two pistons so the next downward stroke of the master piston will force the fluid from the discharge port.

Abstract: A variable speed ratio system for the controlled dispensing of a plurality of non-compressible fluids at high pressure, principally for use in reaction injection molding processes. Each of the pistons in two or more displacement cylinders that contain the fluids to be mixed is connected via a rack gear to the piston of a hydraulic driving cylinder, all hydraulic cylinders being connected to a common source of pressure. A variable speed change gear train connected to each rack gear will control the speed ratios of the displacement pistons irrespective of the fluid viscosities or mixing orifice sizes while the gears are subjected to only the differences in forces acting on the displacement piston rods.