Forward-reverse valve for elevating scraper drive

Claim 1

In a hydraulic system comprising a fluid flow circuit having a fluid supply source including a pump and a tank, a reversible hydraulic motor, conduit means for communicating between said source and said motor, inlet control valve means for directing fluid through said conduit means in a forward or reverse direction for operating said motor in a forward or reverse direction, and exhaust valve means for communicating return fluid from said motor to said tank, the improvement comprising: a valve housing having first and second bores therein, said valve housing being disposed in said circuit between said supply source and said motor so that forward fluid flow within said circuit is sequentially directed from said supply source, through said first bore, through said motor, and through said second bore to said tank, and so that reverse fluid flow within said circuit is sequentially directed from said fluid supply source, through said second bore, through said motor, through said first bore through said exhaust valve means and to said tank; first pilot operated check valve means disposed within said first bore for regulating forward fluid flow from said supply source to said motor, said first check valve means opening in response to accumulated fluid pressure when fluid is flowing in a forward direction to permit fluid flow from said fluid supply source, through said first bore, to said motor, and pilot means responsive to pressure in said second bore for opening said first check valve means when fluid is flowing in a reverse direction; and, second pilot operated check valve means disposed within said second bore for regulating return fluid flow between said motor and said tank, said second check valve means including pilot means for opening said valve in response to accumulated pressure within said first bore to permit fluid flow from said motor, through said second bore, to said tank, when fluid is being supplied in said forward direction, and said second check valve means being responsive to a drop in pressure in said conduit means between said second check valve means and said motor to provide direct flow of fluid from said tank to said motor, and including relief means responsive to an excess of pressure in said conduit means between said second check valve means and said source to open said second check valve means to relieve said excess pressure to said tank via said second check valve means.