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 .