Airfoil changeover device

In an air-operated reciprocating piston pump having a hollow center displacement rod comprising a top end with a piston located about said top end and a valve assembly comprising top and bottom air intake plates located above and below said piston respectively, said intake plates being attached to each other by spacers passing through a plurality of circumferentially spaced air passages in said piston, the improvement comprising means for increasing and utilizing air velocity during bottom changeover to increase axial changeover force and reliability, said velocity increasing means comprising an annular airfoil comprising a chevron cross-section with a base facing axially downward and an apex facing axially upward, said airfoil being located beneath said bottom air intake plate.