A hydraulic system for a working machine, includes a hydraulic device to change a flow rate of an operation fluid. The hydraulic device includes a first hydraulic receiver to which the operation fluid is applied, a second hydraulic receiver to which the operation fluid is applied, and a movable portion to be moved by the operation fluid applied to any one of the first hydraulic receiver and the second hydraulic portion. A hydraulic system further includes a differential pressure regulator to supply the operation fluid to the first hydraulic receiver and the second hydraulic receiver, the differential pressure regulator being configured to regulate a differential pressure between a first pressure that is a pressure of the operation fluid applied to the first hydraulic receiver and a second pressure that is a pressure of the operation fluid applied to the second hydraulic receiver.

A hydraulic system of a construction machine includes: a pump that supplies hydraulic oil to a hydraulic actuator; a control valve on a center bypass line extending from the pump to a tank, the control valve including a bypass passage; an unloading valve on the center bypass line downstream of the control valve; and a controller that controls the unloading valve. The control valve is configured such that an opening area of the bypass passage is greater than an opening area of the unloading valve while an operation signal outputted from an operation device increases from a predetermined value to a first setting value, and such that the opening area of the bypass passage is less than or equal to ¼ of a maximum opening area of the bypass passage when the operation signal is greater than or equal to a second setting value greater than the first setting value.

A hydraulic control assembly includes means for holding pressure in a cylinder to inhibit boom or arm drop of a machine in the event that a hose between the cylinder and a main control valve (MCV) ruptures. The pressure holding means of the hydraulic control assembly include a hydraulic valve and a parts-in-body check assembly both configured for insertion into a valve cavity defined by a valve body. The hydraulic valve comprises a proportional piloted valve that controls pressure.

An improved servovalve for a seismic vibrator or vibration machine which includes a left additional passageway conducting a portion of sampled pressure from a left cylinder pressure chamber to only a portion of the right end drive surface of the spool, wherein the portion of the right end drive surface is less that of the entirety of the right end drive surface; and a right additional passageway conducting a portion of sampled pressure from a right cylinder pressure chamber to only a portion of the left end drive surface of the spool, wherein the portion of the left end drive surface is less that the entirety of the left end drive surface; thereby providing at least two additional passageways configured to provide linear proportional pressure feedback in spool movement control.

A load sense pressure regulating system is provided. The load sense pressure regulating system can be operable between a flow regulation mode and a pressure limiting mode. When the load sense pressure control system is in the flow regulation mode, flow between a load sense inlet and a pilot vent are metered by a main poppet. The load sense pressure regulating system can also include a control valve downstream from the pilot vent that is configured to control a relief setting of a relief valve to regulate the load sense pressure within a desired operating range.

An integral flapper and nozzle structure for a servo valve assembly whereby the flapper, orifices and nozzles are formed by sheets of metal formed into a single component.

Provided is a work machine with which responsiveness of a hydraulic actuator can be improved when driving the hydraulic actuator through an electric lever-type operation device. A controller 100 further includes: an operation direction determining section 116 configured to determine operation directions of operation devices 2a and 2b; and a standby pressure switching command section 117 configured to output a standby pressure switching command to a first target pilot pressure correction section 112 or a second target pilot pressure correction section 113 which corresponds to a solenoid proportional valve that does not correspond to the operation direction from among first solenoid proportional valves 41a, 42a, 42b, 43a, 43b, and 44a and second solenoid proportional valves 41b, 42c, 42d, 43c, 43d, and 44b. The first target pilot pressure correction section and the second target pilot pressure correction section are configured to switch a first standby pressure α to a second standby pressure β set lower than the first standby pressure in a case in which the standby pressure switching command has been inputted.

An example valve housing comprises: a longitudinal bore; a first and second workport passages intercepting the longitudinal bore and configured to be fluidly coupled to an actuator; a first and second return cavities intercepting the longitudinal bore; a first inlet port configured to be fluidly coupled to a first source of fluid; a second inlet port configured to be fluidly coupled to a second source of fluid; an outlet port fluidly coupled to the first and second return cavities and configured to be fluidly coupled to a reservoir; a first dual-wing passage fluidly coupled to the first inlet port; a second dual-wing passage fluidly coupled to the second inlet port; and a third dual-wing passage fluidly coupled to the second inlet port.

An example valve includes: a plurality of ports comprising: (i) a first port, (ii) a second port configured to be fluidly coupled to a reservoir, and (iii) a third port configured to be fluidly coupled to a source of fluid; a spool slidably accommodated in a sleeve; an annular chamber formed between the spool and the sleeve, wherein the annular chamber is fluidly coupled to the first port, and wherein a first flow area is formed between the spool and the sleeve to fluidly couple the annular chamber to the second port via the first flow area; and a solenoid coil, wherein when the solenoid coil is energized, a solenoid force the spool, thereby causing the spool to move, forming a second flow area between the spool and the sleeve to fluidly couple the third port to the annular chamber via the second flow area.

A control system for construction machinery, includes a hydraulic pump, first and second actuators connected to the hydraulic pump through first and second parallel lines respectively, first and second control valves installed in the first and second parallel lines respectively and configured to control operations of the first and second actuators, first and second spool displacement adjusting valves configured to control displacement amounts of the spools of the first and second control valves, and a controller configured to output a control signal to the first and second spool displacement adjusting valves corresponding to a manipulation signal of an operator, and configured to limit a spool displacement amount of the second control valve according to the manipulation signal for the first actuator when the manipulation signal for a multiple operation of the first and second actuators is received.