Abstract: A fluid-driven proportioning pump for dispensing precise volumes of at least three different fluids includes a drive cylinder housing a correspondingly formed drive piston which divides the drive cylinder into first and second drive fluid chambers and is propelled in a reciprocating motion by a pressurized drive fluid. Each face of the drive piston is provided with projecting porportioning pistons which extend into proportioning cylinders that open into each drive fluid chamber and being directed toward the drive piston. An over-center mechanis triggered by movement of the drive piston at the extremes of the strokes for its reciprocating motion operates valving which admits the pressurized drive fluid into alternate of the drive fluid chambers. The over-center mechanism is activated by loop springs or preferably by pairs of C-shaped springs, and is housed entirely within the drive cylinder.