Abstract: A delivery control device for hydraulic pumps suitable for controlling the pump delivery such that the pump's delivery characteristics are not influenced by load acting on actuators is disclosed. The device also reduces the pump delivery in cases where no actuator is being operated but instantly increases the pump delivery in the event either actuator is operated. The device has a branch line branched from a pilot line and adapted for draining the swash plate's regulating pilot oil from the pilot line to a return tank, and a relief valve provided in the branch line, selectively opened in response to a preset pressure applied thereto. The preset pressure for opening the relief valve is the delivery pressure of the hydraulic pump.

Abstract: A variable priority device for heavy construction equipment for establishing a priority of the boom over the bucket by limiting an amount of fluid passing through a bucket-side parallel fluid line when the boom operates alone and thereby decreasing the amount of fluid supplied to the bucket actuator. The device is installed in the bucket-side parallel fluid line and adapted to be switched between an orifice state and an orifice release state, the priority control valve being initially maintained at the orifice release state by a resilience device while being switched from the orifice release state to the orifice state against a resilience of the resilience device in response to a pilot pressure for moving the spool of a boom-side switching valve communicating with the boom actuator.

Abstract: A priority control valve used in a hydraulic apparatus for supplying fluid delivered from a single pump to at least two actuators respectively via parallel fluid lines, the actuators operating independently or in combination with each other. The variable priority device includes a priority control valve installed in the parallel fluid line associated with one of the actuators and adapted to be switched between an orifice state and an orifice release state, the priority control valve being initially maintained at the orifice release state by resilience means while being switched from the orifice release state to the orifice state against a resilience of the resilience means in response to a pilot pressure for moving the spool of a control valve for the other actuator.

Abstract: A device for sensing actuator operating signal in a hydraulic system is disclosed. The device has auxiliary valves directly coupled to the directional control valves respectively, the internal lines of which auxiliary valves are opened or become orifices in accordance with positions of spools of their associated directional control valves. A fluid line extends from a hydraulic pump to a return tank after passing the auxiliary valves in a series. The device also has two elements for detecting fluid pressure at two given points along the fluid line. An additional orifice is formed in the hydraulic line between the auxiliary valves and the pressure detecting elements is provided in the hydraulic line before and after the additional orifice.

Abstract: A straight travelling apparatus for heavy construction equipment such as excavator or crane, including a straight travel valve disposed in both lines respectively branching from first and second hydraulic pumps and switched between a first state at which a fluid delivered from the first hydraulic pump is supplied to a right travel motor and a part of the actuators of a working system while a fluid delivered from second hydraulic pump is supplied to a left travel motor and the remaining part of the actuators of the working system and a second state at which the fluid delivered from the first hydraulic pump is supplied to both the right and left travel motors while the fluid delivered from the second hydraulic pump is supplied to all actuators of the working system, first and second pilot fluid lines both branching from the pilot pump, a connecting fluid line adapted to communicate the first and second pilot fluid lines with each other, a fluid line branching from the connecting fluid line, and a relief check v