An arrangement for operating a load-controlled hydraulic system of an agricultural tractor, includes a hydraulic pump generating a system pressure and having an actuating device to adjust a displacement volume, a hydrostatic vehicle steering system connected to the hydraulic pump and having a steering orbitrol and a first load-indicating pressure, a pressure-regulating valve connected upstream of the steering orbitrol and actuated via a pressure difference decreasing across a throttle element counter to a predetermined restoring force in accordance with the first load-indicating pressure, a second hydraulic consumer connected to the hydraulic pump and feeding a second load-indicating pressure back to a shuttle valve arrangement, which compares and transmits the respectively higher of the first and second load-indicating pressures to the actuating device to adjust the displacement volume, and a pressure-copying valve indirectly feeding back the first load-indicating pressure to the shuttle valve arrangement.

The invention relates to a handling machine comprising a hydraulic steering circuit (3), a first hydraulic control circuit (100), provided with a manual steering device (4), which allows steering cylinders (31-34) of the hydraulic steering circuit (3) to be supplied with power, and a second hydraulic control circuit (200) which is used to control at least one hydraulic actuation cylinder (5) for actuating a handling member of the machine. The second circuit (200) comprises a hydraulic directional control valve (210), a hydraulic connection circuit (600) which is connected to the steering circuit, and a diverter valve (220) to which the connection circuit (600), the hydraulic actuation cylinder (5) and the hydraulic directional control valve (210) are connected. The diverter valve (220) is electrically controllable by a control unit (10) to selectively control the hydraulic actuation cylinder (5) and the same steering cylinders as those which are controllable by the first control circuit (100).

An apparatus for operating a load-controlled hydraulic supply of an agricultural tractor includes a hydraulic pump which is adjustable with respect to the displacement volume for supplying pressurized hydraulic fluid, a proportional valve which is electrically actuatable, a primary hydraulic consumer to carry out a superordinate hydraulic function and to be directly connected to a conveying outlet of the hydraulic pump, a secondary hydraulic consumer to carry out a subordinate hydraulic function and to be connected to the conveying outlet of the hydraulic pump via the proportional valve, and a control unit configured to move the proportional valve into a closed valve position when the control unit recognizes that at least one of a required power of the primary and secondary hydraulic consumers exceeds the conveying capacity of the hydraulic pump and the subordinate hydraulic function of the secondary hydraulic consumer is inactive.

A transportation vehicle includes: a cooling fan that is driven by a hydraulic motor; a heat exchanger that is disposed in a front portion of a vehicle body; a fan control valve that controls a flow of a hydraulic operating fluid supplied to the hydraulic motor; a cylinder control valve that controls a flow of the hydraulic operating fluid supplied to a hydraulic cylinder; and a controller. The fan control valve and the cylinder control valve are connected in tandem to a center bypass line. The fan control valve has a neutral position that makes a first hydraulic pump and the cylinder control valve communicate with each other and makes a suction port and a delivery port of the hydraulic motor and a hydraulic operating fluid tank communicate with each other, and a rotation position that makes the first hydraulic pump and the suction port of the hydraulic motor communicate with each other and makes the delivery port of the hydraulic motor and the hydraulic operating fluid tank communicate with each other.

A transportation vehicle includes: a cooling fan that is driven by a hydraulic motor; a heat exchanger that is disposed in a front portion of a vehicle body; a fan control valve that controls a flow of a hydraulic operating fluid supplied to the hydraulic motor; a cylinder control valve that controls a flow of the hydraulic operating fluid supplied to a hydraulic cylinder; and a controller. The fan control valve and the cylinder control valve are connected in tandem to a center bypass line. The fan control valve has a neutral position that makes a first hydraulic pump and the cylinder control valve communicate with each other and makes a suction port and a delivery port of the hydraulic motor and a hydraulic operating fluid tank communicate with each other, and a rotation position that makes the first hydraulic pump and the suction port of the hydraulic motor communicate with each other and makes the delivery port of the hydraulic motor and the hydraulic operating fluid tank communicate with each other.

A system for hydraulic parallel work systems is provided. The system includes a fixed displacement pump (110), a closed-center circuit (300), an open-center hand metering unit (HMU) (200), and a tank (120). The closed-center circuit is in fluid communication with the fixed displacement pump. The open-center HMU is in fluid communication with the fixed displacement pump at an inlet port (204) of the HMU. The tank is fluidly connected to the inlet port of the HMU when the HMU is inactive.

A hydraulic system includes a pump having a pump outlet, a tank configured to supply fluid to the pump, a hydraulic motor coupled to an air compressor that is configured to supply compressed air to an air brake, a steering gear having an inlet workport and an outlet workport, and a compressor bypass valve. The compressor bypass valve is selectively movable between a first position where fluid flow is provided from the pump outlet to both the hydraulic motor and the inlet workport of the steering gear and a second position where the fluid flow from the pump outlet bypasses the hydraulic motor and is supplied to the inlet workport of the steering gear.

An arrangement for controlling a fluid circuit's flow from alternatively a first and a second pump to a tank via steering unit and steering cylinder of the circuit is disclosed. The arrangement comprises a first flow path including a flow direction control device for preventing a flow to a first inlet in response to a pressure difference across the device, a second flow path including an emergency valve for opening of the second flow path comprising and controlled via a control port a connection between the first and the second flow path in accordance with a position of the flow direction control device between the emergency valve and the first inlet; and a connection for responding to a pressure drop between the first pump and the flow direction control device by opening of the second flow path.