In a control unit of an electromagnetic valve system, a safety circuit includes a first switch and a second switch for switching, by control from a control circuit supply and shutdown of power from a drive power supply to an electromagnetic valve drive circuit. A common line extends to a plurality of electromagnetic valve units and is connected to one end of a plurality of solenoids. A plurality of power lines are connected to the other end of each of the plurality of solenoids. The electromagnetic valve drive circuit includes a plurality of open/close switches for switching, by control from the control circuit, supply and shutdown of power to the plurality of solenoids.

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 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 system including a supply line, an implement-based control valve, an override valve supported by the implement, and a bypass line. The control valve is fluidly coupled to the supply line and configured to regulate a flow of pressurized hydraulic fluid supplied through a downstream actuator line to a hydraulic actuator of the implement. The override valve is fluidly coupled to the actuator line downstream of the control valve and includes a supply position at which the flow of pressurized hydraulic fluid from the control valve passes through the override valve to the hydraulic actuator. The override valve is actuatable to at least one override position at which the flow of pressurized hydraulic fluid from the control valve is cut-off. The bypass line is fluidly coupled between the supply line and the override valve such that a portion of the pressurized hydraulic fluid flows to the hydraulic actuator.

This hydraulic system is provided with: a hydraulic pump; a pilot-type control valve; an electromagnetic proportional valve; a controller; and a pilot pressure switching unit which is capable of switching the electromagnetic proportional valve supply pressure to a first pressure during a normal operation, or to a second pressure lower than the first pressure. The control valve is provided with a bleed-off passage, and is capable of controlling the operating oil pressure supplied to the actuator, according to the opening area thereof. During an emergency operation, the electromagnetic proportional valve supply pressure is switched from the first pressure to the second pressure, the electromagnetic proportional valve is brought into a fully opened state, and the operating oil discharge amount from the hydraulic pump increases and decreases, and the operating oil pressure increases and decreases, and thus the operating speed of the actuator is controlled.

A fluid leakage detection system includes: a measurement unit configured to detect leakage of working oil in a hydraulic cylinder; and a controller configured to acquire a measurement result from the measurement unit, wherein the controller diagnoses that a battery depletion has been caused in a battery in a case in which it is determined that a data from the measurement unit has not been acquired and it is determined that the battery of the measurement unit has been in a low-remaining-battery-level state, and the controller diagnoses that a communication abnormality has been caused in a first communication part of the measurement unit in a case in which it is determined that the data from the measurement unit has not been acquired and it is determined that the battery has not been in the low-remaining-battery-level state.

A hydraulic system including a supply line, an implement-based control valve, an override valve supported by the implement, and a bypass line. The control valve is fluidly coupled to the supply line and configured to regulate a flow of pressurized hydraulic fluid supplied through a downstream actuator line to a hydraulic actuator of the implement. The override valve is fluidly coupled to the actuator line downstream of the control valve and includes a supply position at which the flow of pressurized hydraulic fluid from the control valve passes through the override valve to the hydraulic actuator. The override valve is actuatable to at least one override position at which the flow of pressurized hydraulic fluid from the control valve is cut-off. The bypass line is fluidly coupled between the supply line and the override valve such that a portion of the pressurized hydraulic fluid flows to the hydraulic actuator.

A method controls a hydraulic actuator drive that has an actuator and the position of the actuator is set by at least one electrohydraulic proportional valve that has at least one electrical input and at least one hydraulic output. First, the position of the actuator is detected and an actual position value is generated therefrom. Second, a target position value is specified in dependence on a default for a desired position of the actuator and a target/actual value difference is corrected by the at least one electrohydraulic proportional valve, so that the actuator assumes a position corresponding to the target position value. The method is characterized in that the target position value is also varied if the default remains unchanged for a desired position of the actuator.

The disclosure relates to an electro-hydraulic control system for directing fluid to at least one hydraulic actuator, the system comprising at least one electronic controller; first and second pilot valves being electrically connected to the at least one electronic controller which is arranged to control the operation of the first and second pilot valves, third and fourth pilot valves being electrically connected to the at least one electronic controller which is arranged to control operation of the third and fourth pilot valves. A pilot operated main valve is configured to control fluid flow to at least one hydraulic actuator. Each of the first and second pilot valves and the third and fourth pilot valves is a fail-safe pilot valve arranged to drain a regulated outlet port to a low pressure reservoir if a spool of the fail-safe pilot valve becomes stuck in an open state.

An online method for reconfiguring pressure and position sensors in a hydraulic system is disclosed. In one step, a sensor drift condition, a recalibration request, or an unisolated fault condition is detected. In another step, a system pressure sensor or another sensor, such as a load-sense pressure sensor, is verified as a trusted master reference sensor. Another step includes measuring and recording a first pressure reading at the master reference sensor and first voltage readings associated with first, second, third, and fourth pressure slave sensors at a first pump pressure set point. Another step includes, repeating the previous step at a second pump pressure set point. A new gain and offset for each of the first, second, third, and fourth pressure sensors can be calculated based on a comparison of the recoded first and second pressure readings and the recorded first and second voltage readings.

A system and method for controlling a valve increases the availability of a control valve assembly used in a control process. A pair of positioners are arranged in a high-availability configuration and individually coupled to a controller. A first positioner includes an output coupled to a switch and a second positioner includes an output coupled to the switch. The operating state of the first positioner is monitored and the output of the first or second positioner allowed to pass through the switch to the control valve is dependent upon the operating status of the first positioner.