In one aspect, a system for controlling the supply of hydraulic fluid to an implement of a work vehicle may generally include a pump, a control valve coupled to the pump and first and second fluid lines provided in flow communication with output ports of the control valve. The system may also include a pressure control valve provided in flow communication with the second fluid line that is configured to regulate a fluid pressure of the hydraulic fluid being supplied to a hydraulic cylinder of the implement. Additionally, the system may include a bypass fluid line configured to provide a flow path for hydraulic fluid between the pump and the second fluid line that is independent of the control valve and a load sensing line configured to provide an indication of the fluid pressure of the hydraulic fluid being supplied to the hydraulic cylinder.

Hydraulic workover system having at least two sets of hydraulic cylinders coupled with a single load. A plurality of control valves transitionable between a closed position and an open position, the plurality of control valves having at least one extend control valve disposed between each set of hydraulic cylinders and an extend supply pump, at least one retract control valve disposed between each set of hydraulic cylinders and a retract supply pump, and at least one float control valve disposed between each set of hydraulic cylinders and a float supply pump. A logic control system coupled with the plurality of control valves and configured to transition the plurality of control valves between the closed and open position, thereby controlling flow between the at least two sets of hydraulic cylinders and the extend supply pump, retract supply pump, and float supply pump.

A control valve unit includes a pilot-operated first operation valve 21 that can be operated to a first closed position at which a first oil passage 41 and a tank port 24 are disconnected from each other and a first open position at which the first oil passage 41 and the tank port 24 are connected to each other; and a pilot-operated second operation valve 22 that can be operated to a second closed position at which a second oil passage 42 and the tank port 24 are disconnected from each other and a second open position at which the second oil passage 42 and the tank port 24 are connected to each other.

A header is supported by a pair of hydraulic float cylinders, where a float pressure to the cylinders is directly controlled by an electronic control supplying a variable control signal to a PPRR valve arrangement to maintain the float pressure at a predetermined value. At the set pressure a predetermined lifting force is provided to the header. A position sensor is used to generate an indication of movement and/or acceleration and/or velocity. The electronic control is arranged, in response to changes in the sensor signal, to temporarily change the control signal to vary the lifting force and thus change the dynamic response of the hydraulic float cylinder. A lift force greater than that required to lift the header can be provided by a lift cylinder and can be opposed in a controlled manner to apply a controlled downforce by the back of the same cylinder or by a separate component.

A floating control system for a fixed displacement pump system is disclosed, which relates to the technical field of floating mechanisms and includes: a fixed displacement pump, floating control valves, a floating mechanism, boom function valves, an actuator and a control device, where the fixed displacement pump, the floating control valves and the floating mechanism are connected in sequence, the fixed displacement pump, the boom function valves and the actuator are connected in sequence, the floating control valves include a pressure reducing valve and a floating switching valve, and the boom function valves include a fixed differential overflow valve and a proportional directional valve; and the fixed differential overflow valve and the proportional directional valve are connected in parallel between the fixed displacement pump and an oil return tank, the floating switching valve and the fixed differential overflow valve are connected through a feedback oil path.

In one aspect, a system for controlling the supply of hydraulic fluid to an implement of a work vehicle may generally include a pump, a control valve coupled to the pump and first and second fluid lines provided in flow communication with output ports of the control valve. The system may also include a pressure control valve provided in flow communication with the second fluid line that is configured to regulate a fluid pressure of the hydraulic fluid being supplied to a hydraulic cylinder of the implement. Additionally, the system may include a bypass fluid line configured to provide a flow path for hydraulic fluid between the pump and the second fluid line that is independent of the control valve and a load sensing line configured to provide an indication of the fluid pressure of the hydraulic fluid being supplied to the hydraulic cylinder.

A hydraulic system of a work machine includes a first hydraulic device to operate in a first operation mode while pressure of hydraulic oil supplied from a hydraulic pump via a first oil passage is equal to or higher than a first pressure threshold. The hydraulic oil in the first oil passage is to be discharged via a second oil passage. A pilot check valve is provided in the second oil passage and has a pilot port to receive a pilot pressure of the hydraulic oil. The pilot check valve is closed to stop discharging the hydraulic oil in the first oil passage through the second oil passage while the pilot pressure is higher than or equal to the second pressure threshold. The pilot check valve is opened while the pilot pressure is less than the second pressure threshold.

Disclosed are a hydraulic control system for boom floating of an excavator and a control method thereof. In the hydraulic circuit, a main pump supplies oil to the boom cylinder through a boom reversing valve, and two working ports of the boom reversing valve are connected to a rod cavity and a rodless cavity of the boom cylinder respectively. A rod cavity floating valve and a rodless cavity floating valve are connected to an oil circuit between the rod cavity of the boom cylinder and the boom reversing valve and an oil circuit between the rodless cavity of the boom cylinder and the boom reversing valve respectively. A pilot oil pump and a handle pilot valve are arranged on the pilot oil circuit, an oil inlet of the handle pilot valve is connected to the pilot oil pump.

A harvester implement includes a linkage system supporting a harvester head, and a float system having an internal fluid pressure that is controllable to achieve a ground contact force between the harvester head and the ground surface. A controller is operable to receive a user defined input commanding a desired ground contact force, and define an initial value of the internal fluid pressure to achieve the desired ground contact force. The controller may then automatically detect a change in an operating parameter of the harvester head during operation, and automatically re-define the initial value of the internal fluid pressure to provide an adjusted value of the internal fluid pressure to maintain the desired ground contact force based on the detected change in the operating parameter of the harvester head during operation.