Blade lift float circuit for motor graders

Claim 1

In a vehicle of the type having a work tool mounted thereon, at least one double acting cylinder, means connecting said cylinder to said work tool for selectively moving the same; a fluid circuit comprising: a fluid source; means for pressurizing said fluid; first control valve means for selectively communicating fluid from said means for pressurizing fluid via first passage means to rod and head ends of said cylinder; normally closed second control valve means including a housing defining bore, a pair of check valves mounted in said bore and each operatively connected via second passage means to said first passage means and normally blocking communication from a respective rod or head end of said cylinder, a pair of back-to-back pistons reciprocally mounted in said bore and defining with said bore a working chamber therebetween, said housing further defining a sole internal passage means directly communicating each of said check valves one to the other for receiving fluid therefrom upon opening thereof and further directly communicating with said fluid source; and, third control valve means comprising a two position directional control valve movable between a normally closed position communicating said working chamber with said fluid source and an open position communicating pressurized fluid from said means for pressurizing fluid to said working chamber for urging said back-to-back pistons apart to directly interconnect said rod end of said cylinder, said head end of said cylinder and said fluid source.