Abstract: Apparatus is disclosed for delivering two or more liquids in predetermined ratios, where the liquids are pumped by separate reciprocating pistons, the stroke of each piston being independently adjustable by means of a pivotal piston rod anchor and an adjustable piston arc control mechanism. All of the pistons are interconnected by means of an angularly rotating metering shaft which is in turn connected to a toggle valve mechanism for reversing the piston drive control upon reaching a predetermined amount of angular rotation. Since all interconnected pistons pass through the same angular value, but along independently adjustable arcs of travel, the respective strokes of each piston may be thereby controlled. A novel air valving mechanism for accomplishing the reversal and control of valves which regulate the fluid flow in contact with the respective pistons forms a part of the present invention.