Circuit for pitch and tilt of dozer blade

Claim 1

In a tractor having a hydraulic circuit including a pump and a reservoir, and a dozer blade mounted on push arms with a pair of hydraulic rams having head and rod ends extending between the blade and each of said push arms, an improved control for pitching said blade comprising: a directional control valve selectively connecting selected ends of said rams of said pump and reservoir for simultaneous extension or simultaneous retraction of the rams; a first diverter-combiner spool valve interposed between said pump and reservoir and the head ends of said rams and operative to provide equal flow to said rams during extension thereof while combining the flow therefrom during retraction of the rams; a second diverter-combiner spool valve interposed between said pump and said revervoir and the rod ends of said rams and operative to combine the flow from said rams during extension thereof and to provide equal flow thereto during retraction of the rams; and a selector valve positioned downstream of said control valve, said selector valve having two positions, one in which communication of said pump and reservoir is achieved with both rams through said diverter-combiner valves and the other in which communication of said pump and reservoir is achieved with only one ram independently of said diverter-combiner valves.