Abstract: The invention concerns a hydraulic valve arrangement with a supply connection arrangement, which has a high-pressure connection (P) and a low-pressure connection (T), a working connection arrangement, which has two working connections (A, B), which can be connected with a consumer, a directional valve and a compensation valve arranged between the directional valve and the supply connection arrangement, the pressure outlet of the compensation valve being connected with a pressure inlet of the directional valve. It is endeavoured to avoid dangerous situations, which occur because of uncontrolled pressures. For this purpose, it is ensured that the compensation valve has a relief outlet, which can be connected with the pressure outlet.

Abstract: The invention concerns a hydraulic dual circuit steering system with first circuit having a first control unit and a first steering motor connected with the control unit via working connections, a second circuit having a second control unit and a second steering motor connected with the control unit via working connections, a changeover valve, which in a first position activates the first circuit and deactivates the second circuit and in a second position activates the second circuit and deactivates the first circuit. To improve the steering behaviour, in the first position of the changeover valve the working connections of the second circuit and in the second position of the changeover valve the working connections of the first circuit are connected with a pressure source.

Abstract: A hydraulic valve arrangement includes a control valve (3), which, in a first operating position (5), connects a motor connection (21) with a pump connection, in a second operating position (6), connects a motor connection with a tank connection, and, in a locking position (4), disconnects the motor connection (21) from the pump and tank connection. A locking valve (19) is coupled between the control valve (3) and the motor connection (21), dividing the motor line (22) into a first section (23) allocated to the control valve (3) and a second section (24) allocated to the motor connection (21). For the locking valve (19), a pressure release valve (20) in the shape of a seated valve is provided that is fixed to the housing thereby improving control accuracy.

Abstract: The invention concerns a hydraulic valve arrangement with locking function. It has a control valve (9), which in two operating positions (11, 12) connects one motor connection (A) with a pump connection and a second motor connection (B) with a tank connection and vice versa, and in a locking position (10) separates both motor connections (A, B) from pump and tank connection. Further, there are two lock valves (16, 17), each connected between the control valve (9) and one of the motor connections (A, B).

Abstract: The invention concerns a hydraulic valve arrangement with a control valve (3), which, in a first operating position (5), connects a motor connection (21) with a pump connection, in a second operating position (6), connects a motor connection with a tank connection, and, in a locking position (4), disconnects the motor connection (21) from the pump and tank connection. A locking valve (19) is coupled between the control valve (3) and the motor connection (21), dividing the motor line (22) into a first section (23) allocated to the control valve (3) and a second section (24) allocated to the motor connection (21). For the locking valve (19), a pressure release valve (20) in the shape of a seated valve is provided. The operating element (32) of said pressure release valve (20) is loaded in the closing direction by the pressure in the first section (23) and a spring (36) and in the opening direction by a constant control pressure (V) acting in dependence of the position of the control valve (3).

Abstract: The invention concerns a hydraulic dual circuit steering system with

Abstract: A hydraulic valve arrangement with locking and floating function, with a control valve (9), which, for two operating positions (11, 12) connects one motor connection (A) with a pump connection and a second motor connection (B) with a tank connection and vice versa, in a floating position (13) connects both motor connections (A, B) with the tank connection and in a locking position (10) separates both motor connections (A, B) from the pump and tank connections. Further, there are two closing valves (16, 17), each being connected between the control valve (9) and a motor connection (A, B) and each having a piston loaded by a spring and limiting a spring chamber, the spring chambers being pressure releasable. Characteristic of this valve arrangement is that lifting valves (18, 19) are provided for the pressure release, which valves are operated by a control pressure depending on the position of the control valve (9). This improves the operating reliability.

Abstract: A hydraulic control system for work vehicles including a control unit to control the steering wheels of a vehicle via a cylinder and a priority valve which by a first load-sensing system controls the pressure fluid flow to the control unit and to a subsequent proportional valve group. By a second load-sensing system the proportional valve group controls the pressure fluid flow to secondary hydraulic motors or work cylinders to control the work tools of the vehicle. The control system also includes an open-centre valve connection and a fixed displacement pump. The first load-sensing system is connected with a second load-sensing system, whereby drop-off of the pressure fluid flow to the control unit is avoided at simultaneous operation of the latter and of one or several of the proportional valves as is the case with known control systems. Hereby a control system is provided which is particularly agreeable to operate for the driver of the work vehicle.

Abstract: A hydraulic system with a pressure source controllable via a load sensing signal, a pressure sink, at least two working sections, each having a hydraulic consumer and a control valve with a load sensing signal connection and at least one back-pressure valve arranged in a tank pipe between the control valve and the pressure sink. In such a system the pressure required from the pump in the neutral position must be as low as possible. On the other hand, however, oscillations should not occur, when an external force acts on another hydraulic consumer in the neutral position of a control valve. In the neutral position of the control valves the load sensing signal connection is therefore connected with the pressure sink via an auxiliary tank pipe by-passing the back-pressure valve.

Abstract: The invention concerns a control valve with a housing, having a pump connection, a tank connection device, a working connection device and a load pressure connection device, each connected with an opening device in a control surface, and with a slide, arranged movably in the housing and co-operating with the control surface, the slide having grooves and/or channels, so that it connects or separates predetermined opening devices with/from each other. In such a control valve the tightness must be improved. For this purpose an additional auxiliary tank connection device is provided, which is connected with an auxiliary tank opening device in the control surface. The slide has an auxiliary tank pipe or groove, which, in its neutral position, connects the auxiliary tank opening device with the load pressure opening device.

Abstract: A hydraulic control valve for controlling flow between a pump, a hydraulic device, and a vessel containing hydraulic fluid. The control valve has an elongated valve slide which is slidably mounted in an elongated valve housing. The valve has three positions, a central neutral position, a float position axially offset in one direction from the neutral position and a constant pressure position axially offset in the opposite direction from the neutral position. In the neutral position, flow of hydraulic fluid to the hydraulic device is inhibited. In the float position, connection is such that a raised device, such as a hydraulically operated bucket, is lowered slowly by gravity until it rests on the ground or another object. In the constant pressure position, the valve connects pump pressure to the load sensing circuit to facilitate, for example, shaking of a bucket of a piece of earth moving equipment.

Abstract: There is provided control apparatus for controlling fluid flow between a bidirectional motor, a pump and a container, and includes a control valve that has a slide operative between neutral and first and second operative positions. A compensating valve is provided in the supply conduit that holds the upstream pressure drop at the control valve substantially constant and is controlled by load pressure sensing circuitry. The load pressure circuitry includes two branches that are connected through a change over valve to the compensating valve. There is provided an over pressure valve and a throttle point in each branch, each branch being connected to a load pressure sensing orifice of the control valve housing and fluidly connected through the slide to one of the housing motor orifices, the one depending upon whether the slide is in its first or in its second position.