Abstract: A hydraulic circuit is disclosed for driving a bidirectional hydraulic motor from a pump via a hand operated directional control valve, as for propelling an earthmover or actuating an implement assembly thereon. For mitigating an abrupt pressure rise as when the motor is set into or out of rotation, the circuit has a pair of oppositely directed dual pressure relief valves connected in parallel with each other between a pair of main lines extending between motor and directional control valve. Each dual pressure relief valve is normally conditioned to pass at a predetermined lower pressure the pressurized fluid from one of the main lines and to pass at a predetermined higher pressure the pressurized fluid from the other main line.

Abstract: A hydraulic brake valve system for use in a hydraulic circuit consisting of driving and braking fluid lines and including therein at least a hydraulic motor for the actuation of an inertia body such as, for example, a construction vehicle or work implements thereof has a counterbalance valve, a cross-over safety valve, a drain change-over valve and a timer valve. The cross-over safety valve consists of two common relief valves, each having two pressure receiving surfaces and adapted to relieve pressurized fluid acted on one of the pressure receiving surfaces at a low pressure and relieve pressurized fluid acted on the other pressure receiving surface at a high pressure, wherein the first port of one of said relief valves is connected with said driving fluid line and the second port thereof is connected with said braking fluid line, whilst the first port of the other relief valve is connected with said braking fluid line and the second port thereof is connected with said driving fluid line.

Abstract: A hydraulic excavator is disclosed which includes two sets of manual control valves for selectively placing a pair of variable displacement pumps in and out of communication with hydraulically driven components such as propelling motors, arm cylinders and boom cylinders. In order to minimize the per-cycle displacement of the pumps when same are discommunicated from all the driven components, a sensing valve is provided which is pilot operated from the sets of manual control valves. When all the manual control valves are in neutral, the sensing valve directs pressurized fluid from a charging pump to a pump-displacement adjustment mechanism thereby causing same to reduce the per-cycle displacement of the pumps to a minimum.

Abstract: A flow divider valve assembly for dividing a flow of fluid between a priority flow device, such as a power steering system, and an excess flow device, such as an auxiliary mechanism. The flow divider valve assembly comprises a valve body defining an inlet port to be connected to a source of fluid under pressure, a priority flow outlet port, an excess flow outlet port and a valve bore interconnecting the ports, and a valve spool axially movable within the valve bore, the valve spool having formed therein an axial bore for permitting a constant communication between the inlet port and the priority flow outlet port. A first restrictor is disposed between the inlet port and the priority flow outlet port and a second restrictor is disposed between the inlet port and the excess flow outlet port. Restriction rate of the first restrictor is made larger than that of the first restrictor.