Bosch Rexroth R900704916

Pilot control valve type 4WRAP 6 W7.3X/G24… (1st stage) The pilot control valve is a direct operated proportional valve. The control edge geometry has been optimized for the use as pilot control valve for proportional directional valves type 4WRKE. The proportional solenoids are pressure-tight, wet-pin DC solenoids with detachable coils. They convert the electric current proportionally into mechanical force. An increase of the current results in a correspondingly higher solenoid force. The set solenoid force will remain constant over the entire control stroke. The pilot control valve mainly consists of the housing (1), the proportional solenoid (2 and 3), the valve control spool (4) and springs (5 and 6). In non-actuated state both actuators are connected to the tank. If one of the two solenoids (2 or 3) is excited, the magnetic force will move the valve control spool (4) towards the spring (5 or 6). After having overcome the overlap area, the connection of one of the two actuators to the tank is blocked and the connection to the pressure chamber is made. There is a flow from P to the control chamber of the main stage. Valves of type 4WRKE are 2-stage proportional directional valves. They control the flow direction and size. The main stage is position-controlled so that the control spool position is independent from flow forces also in the case of bigger flows. The valves mainly consist of the pilot control valve (1), the housing (8), the main control spool (7), the covers (5 and 6), the centering spring (4), the inductive position transducer (9) and the pressure reducing valve (3). If there is no input signal, the main control spool (7) will be kept in the central position by the centering spring (4). Both control chambers in the covers (5 and 6) are connected to the tank via the valve control spool (2). The main control spool (7) is connected to suited control electronics via the inductive position transducer (9). Both the position change of the main control spool (7) and the change of the command value at the junction summing of the amplifier create a voltage difference. During the comparison of command value and actual value, a possible control deviation is determined via the electronics and the proportional solenoid of the pilot control valve (1) is supplied with current. The current induces a force in the solenoid which operates the control spool via a plunger in a row. The flow which is activated via the control cross-sections leads to an adjustment of the main control spool. The main control spool (7) with the core of the inductive position transducer (9) attached to it is displaced until the actual value corresponds to the command value. In controlled state, the main control spool (7) is force-balanced and kept in this controlled position. The control spool stroke and the control opening change proportionally to the command value. The control electronics is integrated in the valve. By adjusting valve and electronics, the deviation in series production of the devices is kept low. The tank lines must not be allowed to run empty; with corresponding installation conditions, a preload valve (preload pressure approx. 2 bar) must be installed. Valve particularities The 2nd stage is basically set-up of modules of our proportional valves. The zero point adjustment at "zero point main stage" is made at the factory and can be adjusted in a range of ± 30% of the nominal stroke via a potentiometer in the control electronics. Access in the integrated control electronics by removing a plug screw on the front side of the cover housing. When the pilot control valve or the control electronics are exchanged, they are to be re-adjusted. All adjustments may be implemented by instructed experts only. Notice! Changes in the zero point may result in damage to the system and may only be implemented by instructed specialists!