A method is provided for compensating for the flow rate of a variable capacity-type hydraulic pump such that, when a manipulation lever is manipulated, a discontinuous section, which has no change in the discharge flow rate of the hydraulic pump, is eliminated.

A hydraulic excavator 1 includes an engine 16, a main hydraulic pump 17 driven by the engine 16, a plurality of hydraulic actuators driven with pressure oil discharged from the main hydraulic pump 17, a plurality of flow rate control valves adapted to control the flow rate of pressure oil to be supplied from the main hydraulic pump 17 to the respective hydraulic actuators, a pilot hydraulic pump 18 adapted to supply pressure oil for driving the flow rate control valves, and a controller 15 configured to control the discharge flow rate of the pilot hydraulic pump 18. The controller 15 controls the discharge flow rate of the pilot hydraulic pump 18 such that it becomes equal to the sum of requested pilot flow rates determined in accordance with control commands for the respective flow rate control valves and a preset standby flow rate.

A shovel includes a lower traveling body, and an upper swiveling body mounted on the lower traveling body. The upper swiveling body is rotatable. An attachment is attached to the upper swiveling body. A traveling actuator is configured to drive the lower traveling body. An attachment actuator is configured to move the attachment. A control device is provided in the upper swiveling body. The control device is configured to autonomously operate at least one of the traveling actuator and the attachment actuator depending on an inclination of a ground on which the lower traveling body is traveling.

A system for exhausting hazardous stored energy from a pneumatic subsystem of a railcar, comprises: an air supply for delivering air to the pneumatic subsystem of the railcar; and an isolation valve interposed between the air supply and the pneumatic subsystem of the railcar. When the isolation valve is in a normal operating position, a supply port and a delivery port of the isolation valve are in fluid communication with one another, but when the sliding shoe is in the second position, the sliding shoe effectively closes access to the supply port, and the delivery port is in fluid communication with an exhaust port of the isolation valve. The isolation valve further includes a means for locking the sliding shoe in the second position.

An engine-driven oil pump has an engine, a pump unit, an oil diverting device, a manual control unit, and a remote control unit. The engine is connected to the pump unit. The oil diverting device is mounted on the pump unit and selectively pumps hydraulic oil from the pump unit into the manual control unit or the remote control unit. With the engine, the engine-driven oil pump can generate power independently instead of relying on external power supply. Besides, the electromagnetic valve of the remote control unit allows the user to remotely control the oil path of the hydraulic oil, so the user is not required to stay along the engine-driven oil pump to manually switch the oil path, and therefore the engine-driven oil pump is more efficient regarding manpower.

A pressure-limiting unit for a pressure booster for driving hydraulic tools. The unit includes a pneumatic unit that is driven by gas or air pressure, a hydraulic unit connected to the pneumatic unit and having a hydraulic port for connecting the hydraulic tool to the hydraulic unit in a fluid-tight manner and a pressure-limiting valve for adjusting the hydraulic pressure. The unit includes a closing element pushed against a valve seat by a spring element and having a displaceable adjusting element for adjusting the spring force of the spring element. To provide a pressure-limiting unit and a pressure booster for driving hydraulic tools with a pressure-limiting unit, which offer the possibility of making a precise adjustment of the hydraulic pressure in a simple way, the pressure-limiting unit includes a position detection unit connected to the adjusting element to detect the axial position of the adjusting element, an evaluation unit for determining the set hydraulic pressure as a function of the axial position, and an output unit for displaying the set hydraulic pressure.

An engine-driven oil pump has an engine, a pump unit, an oil diverting device, a manual control unit, and a remote control unit. The engine is connected to the pump unit. The oil diverting device is mounted on the pump unit and selectively pumps hydraulic oil from the pump unit into the manual control unit or the remote control unit. With the engine, the engine-driven oil pump can generate power independently instead of relying on external power supply. Besides, the electromagnetic valve of the remote control unit allows the user to remotely control the oil path of the hydraulic oil, so the user is not required to stay along the engine-driven oil pump to manually switch the oil path, and therefore the engine-driven oil pump is more efficient regarding manpower.

In a method of controlling a main control valve of an excavator, when speeds of a boom cylinder and an arm cylinder is increased by handling a boom joystick and an arm joystick, a second arm control spool between a first hydraulic pump and the arm cylinder may be closed. A first boom control spool between the first hydraulic pump and the boom cylinder may be opened to supply a first flux generated from the first hydraulic pump to the boom cylinder. A second boom control spool between a second hydraulic pump and the boom cylinder may be closed. A first arm control spool between the second hydraulic pump and the arm cylinder may be opened to supply a second flux generated from the second hydraulic pump to the arm cylinder.

A pressure-limiting unit for a pressure booster for driving hydraulic tools. The unit includes a pneumatic unit that is driven by gas or air pressure, a hydraulic unit connected to the pneumatic unit and having a hydraulic port for connecting the hydraulic tool to the hydraulic unit in a fluid-tight manner and a pressure-limiting valve for adjusting the hydraulic pressure. The unit includes a closing element pushed against a valve seat by a spring element and having a displaceable adjusting element for adjusting the spring force of the spring element. To provide a pressure-limiting unit and a pressure booster for driving hydraulic tools with a pressure-limiting unit, which offer the possibility of making a precise adjustment of the hydraulic pressure in a simple way, the pressure-limiting unit includes a position detection unit connected to the adjusting element to detect the axial position of the adjusting element, an evaluation unit for determining the set hydraulic pressure as a function of the axial position, and an output unit for displaying the set hydraulic pressure.

A method is provided for compensating for the flow rate of a variable capacity-type hydraulic pump such that, when a manipulation lever is manipulated, a discontinuous section, which has no change in the discharge flow rate of the hydraulic pump, is eliminated.