Abstract: A hydraulic valve assembly comprises a valve body defining first and second valve receptacle bores, a fluid pump, a first fluid passage communicated with the fluid pump, a second fluid passage communicated with a hydraulic load, and a third fluid passage communicated with a fluid reservoir. A first valve sub-assembly including a sleeve enclosing a first valve mechanism therein is disposed within the first valve receptacle body for selectively permitting and blocking introduction of the pressurized working fluid. Also, a second valve sub-assembly including a sleeve enclosing a second valve mechanism therein is disposed within the second valve receptacle bore for selectively establishing and blocking fluid communication between the second and third fluid passage means.

Abstract: This invention aims at providing a hydraulic circuit apparatus for supplying pressurized fluid into cylinders for a work implement arranged such that during normal operation of the work implement the flow rate of fluid discharged by a pump is controlled such that the difference between the discharge pressure of the pump and the load pressure is always kept constant, whilst during inching operation of the work implement the flow rate of fluid discharged by the pump is reduced.

Abstract: An operation valve having a pressure compensation valve of relatively simple non-complicated internal body structure. In the valve body, a load pressure introducing passage, a check valve and a restriction are formed inside the spool comprising the operation valve. An intermediate pressure between an inlet pressure and an outlet pressure of the compensation valve which is arranged in the valve body, may be supplied to a pressure receiving section of the pressure compensation valve through an oil hole of the spool. The operation valve with the pressure compensation valve is of simple construction and may be easily manufactured.

Abstract: In the hydraulic apparatus (1) according to a first aspect of the present invention, mid-pressures between the inlet side and outlet side pressures of a first and a second pressure compensating valves (4, 4') are permitted to act on the flow rate decreasing side pressure receiving surfaces (4b, 4b') thereof through first and second mid-pressure supplying means (13, 13'), thereby restraining operational error and malfunction of the pressure compensating valves (4, 4'). In the hydraulic apparatus (20) according to a second aspect of the present invention. when actuating valves are made to assume neutral position, holding pressures of hydraulic actuators (5, 5') are permitted to act on flow rate decreasing side pressure receiving surfaces (4b, 4b') of pressure compensating valves (4), (4') so that spools of the pressure compensating valves are held at compensating position, thereby improving the response of the hydraulic actuators (5, 5') to lever actuation.

Abstract: A pressure control system in which a pressure in a back pressure chamber of a flow control valve is controlled according to a throttle opening of a pilot valve to locate stationary the valve body of the flow control valve at a position corresponding to the throttle opening of the pilot valve. In the system, a fixed throttle is provided in an oil passage extended to the back pressure chamber of the flow control valve, thereby applying a dampering action to the valve body.

Abstract: A pressure control system in which a pressure in a back pressure chamber of a flow control valve is controlled according to a throttle opening of a pilot valve to locate stationary the valve body of the flow control valve at a position corresponding to the throttle opening of the pilot valve. In the system, a fixed throttle is provided in an oil passage extended to the back pressure chamber of the flow control valve, thereby applying a dampering action to the valve body.

Abstract: A variable pressure control valve arranged to enable a pilot piston having a comparatively small diameter to be used thereby making the whole body of the valve compact. This variable pressure control valve comprises a spool (2) kept in pressure contact with the valve seat of a pressurized fluid inlet port (1) by the resilient force of a compression spring (3); a stationary valve shoe (5) fixed so as to support the base end of the compression spring; and an auxiliary compression spring (6) which urges the spool (2) to the side of the valve seat on one side thereof and is urged by a pilot piston (4) on the other side thereof.

Abstract: This invention provides a hydraulic circuit apparatus for operating a work-implement actuating cylinder arranged such that, during an earth compacting operation using a bucket, a work implement or boom is lowered by its own weight, and during other operations, a part of the fluid under pressure in a lifting chamber of the actuating cylinder is supplied together with pressurized fluid discharged by a pump into a lowering chamber to increase the retracting speed of a piston rod in the work-implement actuating cylinder. The apparatus comprises a spool slidably inserted in a valve bore formed in an operating valve body so that it may be moved between a first actuating position, where a second port connected to the lowering chamber is communicated with a second tank port and a first port connected to the lifting chamber is communicated with a first pump port; and a second actuating position, where the second port is communicated with a second pump port and the first port is communicated with a first tank port.

Abstract: This invention provides a hydraulic circuit apparatus arranged such that when each of operating valves is operated suddenly, the stability of each of actuators is improved, and when the operating valves are kept at their neutral positions, the flow rate of fluid discharged by a variable displacement pump is increased to improve the response of the hydraulic circuit, and when the actuators are supplied with pressurized fluid, pressure compensation is made by pressure compensating valves.

Abstract: A hydraulic circuit arranged to prevent the load pressure in one of the hydraulic actuators at the time of starting from becoming abnormally high thereby preventing fluid under pressure from being relieved by the safety valve when a plurality of hydraulic actuators are operated at the same time, wherein the function of one of the pressure compensating valves is temporarily enhanced by introducing the load pressure in the hydraulic actuator so as to supply a large quantity of fluid under pressure to the hydraulic actuator connected to the pressure compensating valve so that the operating speed of the hydraulic actuator can be increased.

Abstract: A pressure compensating type hydraulic valve wherein a pressure compensation can be made according to the movement of the movable portion of a hydraulic actuator, and the movable portion of the actuator can be stopped against load pressure when it is located at its neutral position. This pressure compensating type hydraulic valve is arranged such that a spool (24) is moved in a valve hole (16) so as to allow a first actuating port (21) and a second actuating port (22) connected with pressure receiving chambers (13.sub.1, 13.sub.2), respectively, defined on both sides of a movable portion (13.sub.

Abstract: This invention relates to an electrohydraulic proportional control valve which continually provides pressurized oil into an oil path on the output side to prevent the existence of air therein and which can move a spool without any time delay when a solenoid is energized, thus improving response. The hydraulic proportional control valve includes a spool which establishes/cuts off communication between an inlet port communicating with a hydraulic pump and an outlet port on the output side, a spring disposed in such a manner as to apply to the base end of the spool such a spring force, which is in equilibrium with the oil pressure force acting on the tip of the spool so as to keep the spool at the position where the inlet port and the outlet port slightly communicate with each other, and a moving rod disposed in such a manner as to oppose the base end of the spool.

Abstract: An apparatus for supplying a pressure oil to a plurality of hydraulic cylinders of a working machine such as power shovels provided with working equipment such as shovels, wherein the cylinders are contracted at the same speed to move down or lower the working equipments at the same speed, so that the working equipment are prevented from suddenly dropping off in operation even if pressure oil passages (a, b) supplying the pressure oil to the cylinders are damaged during operation. The apparatus comprises: a lock valve assembly (B) provided with a valve housing (70) mounted on a cylinder tube of each of the hydraulic cylinders, in which valve housing (70) a check valve (77), a poppet valve (78) and a pilot valve (79) are mounted; and a directional control valve assembly (C) for selectively supplying the pressure oil to a lifting-movement pressure chamber (9a) and a lowering-movement pressure chamber (9b) of each of the hydraulic cylinders through the pressure oil passages (a, b), respectively.

Abstract: A poppet valve device according to the present invention is adapted to sequentially operate a plurality of poppet valves the switching operation of a pilot valve, for example, an electromagnetic solenoid or the like which operates in response to an external input signal. The above-mentioned poppet valve device includes first and second poppet valves (A, B) each of which is constructed so that a poppet (32) for communicating or intercepting an inlet port (30) and an outlet port (31) with or from each other may be moved towards a communicating position by an inlet port side pressure acting upon its pressure receiving portion (32a). The poppet (32) may be moved towards an intercepting position by a pressure acting upon its back pressure chamber (38a, 38b).

Abstract: In a pilot operated control valve system provided with a plurality of valves for controlling a plurality of hydraulic devices such as hydraulic cylinders, there is employed a plurality of valves each of which does not interfere with each other in operation and requires a minimum mounting space in the system to enable the system to be a small system having a construction easily adapted to control a plurality of hydraulic devices and also adapted to simultaneously supply the pressure oil to the hydraulic devices from a pair of hydraulic pumps through the same hydraulic circuit as needs require.

Abstract: In a control valve system provided with a plurality of valves for controlling a hydraulic equipment such as hydraulic cylinders, there are employed a plurality of valves each of which does not interfere with each other in operation and requires a minimum mounting space in the system to enable the system to be a small-sized system having a construction easily adapted to control a plurality of hydraulic equipments.

Abstract: In a pilot operated control valve system provided with a plurality of valves for controlling hydraulic equipment such as hydraulic cylinders, there are employed a plurality of valves each of which does not interfere with each other in operation and requires a minimum mounting space in said system to enable said system to be a small-sized system having a construction easily adapted to control a plurality of hydraulic equipments.

Abstract: A flow control valve assembly, for preventing the pressure oil confined in an inlet port of a valve housing from pulsating and for additionally performing a safety valve function without employing a separate safety valve, has a valve housing which is easy in machining thereof and neat in construction. In the valve housing of the flow control valve assembly is formed a valve-receiving bore (21) in which a poppet (32) and a second spool valve (51), serving as a safety valve, are axially aligned with each other in series. In the valve housing (20), a hydraulic operating oil flows to a communication port (39) of the poppet (32) through an inlet port (23) formed in the valve housing (20), and then further flows to a back-pressure chamber portions (38a, 38b) of the poppet (32) through a variable orifice (44). The pressure oil, having been received in the back-pressure chamber portion (38b), flows out of the portion (38b) to an outer peripheral portion of the second spool valve ( 51).

Abstract: A hydraulic control apparatus has at least two meter-in and two meter-out poppet valves. In order to be compact and deal with a great flow rate, the apparatus is arranged such that a pair of meter-in poppet valves and load check valves are located in an upper horizontal plane, a pair of meter-out poppet valves and solenoid-actuated pilot valves are located in a lower horizontal plane, and a pair of a pilot valve associated with the meter-out poppet valve and a reducing valve associated with the meter-in poppet valve are located in a middle horizontal plane and are respectively disposed in opposed relationship to each other, and the load check valve is vertically located in parallel relationship with the meter-out poppet valve.

Abstract: Disclosed herein is a device for controlling displacement of a variable displacement hydraulic pump comprising a displacement control system for receiving a discharge pressure of the variable displacement hydraulic pump and a discharge pressure of a fixed displacement hydraulic pump to control the displacement of the variable displacement hydraulic pump.