A mechanical proportioner is provided with two pump lowers which are connected together by a yolk underneath an air-operated reciprocating piston pump. The pumps are staggered axially so as to enable overlapping of certain portions thereof thereby enabling the center-to-center distance to be minimized....http://www.google.sh/patents/US6168308?utm_source=gb-gplus-sharePatent US6168308 - Mechanical proportioner
