Abstract: A hydraulic system includes a hydraulic pump, a reservoir, a hydraulic function, such as a cylinder, and a power beyond valve for controlling communication between the pump, the reservoir and the cylinder. The pump provides pressurized fluid at a pump output as a function of the pressure in a load sensing port. For generating a pump controlling load sensing signal in case that the cylinder does not generate such a signal, it is proposed to provide a valve which blocks in a first position or opens in a second position communication between the feed line of the cylinder and the load sensing port of the pump. The valve functions in dependence of control pressures acting on each side of a valve member. A spring is provided biased to urge the valve member to its first closed position. Further, shift valve means are provided to supply selectively different pressures to both sides of the valve member.

Abstract: A valve includes a valve housing having a valve bore with a first valve member movable therein to control fluid communication between a pump, a reservoir and a hydraulic function. The first valve member includes annular grooves which receive pressure controlled seals. A second valve member is movable in the valve bore and is connected to an actuator. The first and second valve members cooperate to form a pre-control valve which controls pressurization of the pressure controlled seals. The second valve member also connects the actuator with the first valve member so that the seals are relieved of pressure before the first valve member is moved.

Abstract: An improved hydraulic control valve is disclosed for providing the metering of fluid to a steering arrangement such as that normally employed on a motorized vehicle. The steering arrangement includes a piston-cylinder assembly, a main pump for supplying pressurized fluid from a fluid reservoir to the control valve and a control pump connected to the control valve which is actuated by a manually operated steering mechanism. The improved control valve includes a housing having an elongated bore formed therein. Movably positioned within the bore is a valve spool which has at least three annular grooves formed thereon separated by a pair of lands. The valve spool also contains a longitudinal bore formed therein which intersects a transverse bore which opens into the centrally positioned annular groove. The valve spool cooperates with the elongated bore to form control pressure chambers at each end thereof.