A pump device includes a variable capacity first pump, a tilt actuator that controls a tilt angle of a swash plate of the first pump in accordance with the control pressure, a regulator that regulates the control pressure in accordance with a front-rear differential pressure of a control valve, a fixed capacity second pump driven by the same drive source as the first pump, the control actuator that operates in accordance with the front-rear differential pressure a resistor so as to drive the regulator to reduce the control pressure in response to an increase in the front-rear differential pressure of the resistor, an auxiliary passage that leads an auxiliary pressure to the control actuator, the auxiliary pressure acting on the control actuator against a upstream pressure of the resistor, and a switch valve that switches between connecting and shutoff the auxiliary passage.

An example valve assembly includes a meter-in valve configured to be fluidly coupled to a first source of pressurized fluid and control fluid flow from the first source of pressurized fluid into a first chamber of an actuator; a counterbalance valve including configured to open and control fluid flow from a second chamber of the actuator to a tank in response to a pilot pressure fluid signal received at a pilot port of the counterbalance valve; and a pressure reducing valve configured to be fluidly coupled to a second source of pressurized fluid and to be fluidly coupled to the pilot port of the counterbalance valve, where the pressure reducing valve is configured to receive pressurized fluid from the second source of pressurized fluid and, when actuated, provide the pilot pressure fluid signal to the pilot port of the counterbalance valve.

An example valve assembly includes a meter-in valve configured to be fluidly coupled to a first source of pressurized fluid and control fluid flow from the first source of pressurized fluid into a first chamber of an actuator; a counterbalance valve including configured to open and control fluid flow from a second chamber of the actuator to a tank in response to a pilot pressure fluid signal received at a pilot port of the counterbalance valve; and a pressure reducing valve configured to be fluidly coupled to a second source of pressurized fluid and to be fluidly coupled to the pilot port of the counterbalance valve, where the pressure reducing valve is configured to receive pressurized fluid from the second source of pressurized fluid and, when actuated, provide the pilot pressure fluid signal to the pilot port of the counterbalance valve.

A method and system for generating electrical power from a wheeled engine-driven vehicle. At least two hydraulic pumps are provided for pumping hydraulic fluid though respective hydraulic fluid outputs of the hydraulic pumps. A first one of the hydraulic pumps is driven by the engine of the vehicle and a second one of the hydraulic pumps is driven by one or more of the road-wheels of the vehicle. Hydraulic fluid pumped by the first and second hydraulic pumps is input in parallel to a hydraulic motor.

Systems and methods for controlling valve assemblies associated with an actuator in an electro-hydraulic system are disclosed. In one method, a controller monitors hydraulic fluid flow for an actuator to identify one valve assembly connected to the actuator as a meter-in valve and another valve assembly connected to the actuator as a meter-out valve. In one aspect, the valve assembly most recently identified as the meter-in valve is controlled to maintain a pressure setpoint and the valve assembly most recently identified as the meter-out valve is controlled to maintain a hydraulic fluid flow rate. The method can also include determining whether the actuator is in a passive state or an overrunning state and controlling the valve most recently identified as the meter-in valve to maintain a first pressure setpoint when the actuator is in a passive state and to maintain a second pressure setpoint when the actuator is in an overrunning state.

A control valve is provided for construction equipment having a holding valve which prevents the natural lowering of an operation apparatus due to the dead weight of the operation apparatus when an actuator is in a neutral position. The control valve includes a valve body, a spool, a holding valve, a control valve, and a pilot pressure control valve. The control valve can save manufacturing cost as well as allow better use of space for construction equipment.

A variable displacement pump supplies hydraulic oil to turning motor via a turning control valve; pair of supply/discharge lines connect turning motor and turning control valve; a pair of make-up lines connect pair of supply/discharge lines to tank, each line having check valve; turning operation device including operating lever and outputting operation signal corresponding to inclination angle of operating lever; a flow rate adjuster adjusts tilting angle of pump; and controller controls flow rate adjuster, such that tilting angle of pump increases in accordance with increase in operation signal outputted from turning operation device. Controller: turning acceleration and at time of constant speed turning, controls flow rate adjuster such that discharge flow rate of pump changes on first regulation line; turning deceleration, controls flow rate adjuster such that discharge flow rate of pump changes on second regulation line, second regulation line having slope less than slope of first regulation line.

An electro-pneumatic controller includes a base having a body, a top surface, and a bore formed within the body; a cover coupled to the base, the cover having an open end with a rim, the rim contacting the top surface of the base; a plurality of fluid flow paths formed within the base; and at least one flame arrestor disposed within one of the fluid flow paths.

A hydraulic suspension system includes a suspension cylinder, a pump, and a control valve therebetween. The control valve includes a spool reciprocally movable between a pump flow position and a tank flow position in which a control port of the control valve is in communication with a pump and a tank, respectively. A piloted logic element in fluid communication with and interposed between the control valve and the suspension cylinder is selectively movable between a through-flow position in which fluid can flow in either direction between a chamber of the suspension cylinder and the control port of the control valve and a blocked position in which fluid is prevented from flowing in or out of the chamber of the suspension cylinder. The logic element is biased to the blocking position, moving to the through-flow position when subjected to a crack pressure delivered from the control port of the control valve.

A motor-generator (27) is connected mechanically to an engine (21) and a hydraulic pump (23). The hydraulic pump (23) delivers pressurized oil to cylinders (12D) to (12F) in a working mechanism (12), a traveling hydraulic motor (25) and a revolving hydraulic motor (26). The revolving hydraulic motor (26) drives a revolving device (3) in cooperation with a revolving electric motor (33). An HCU (36) reduces outputs of the revolving electric motor (33), the revolving hydraulic motor (26), the boom cylinder (12D) and the like such that a ratio of a revolving speed of an upper revolving structure (4) and a movement speed of raising a boom (12A) is held to a ratio in a normal mode (NMODE) at the time of performing a compound movement of a revolving movement and a boom-raising movement in a low speed mode (LSMODE).