20120192975 | HYDRAULIC CONTROL VALVE HAVING A PILOT PISTON WITH FOUR CONTROL EDGES ARRANGED INSIDE THE HOLLOW SPOOL - Provided is a hydraulic control valve with a main stage, having a movable spool valve in a valve housing with at least four ports P, A, B, T to block or release the ports, and provided with control edges formed on piston collars, and with a hydraulic pilot stage provided to control the spool valve of the main stage. If the spool valve of a hydraulic control valve requires a control to release or block the valve housing ports, in addition to electromechanical pilot valves, hydraulically operating pilot stages are also known, in which a pilot valve, controlled by means of a connected drive, regulates a stream of hydraulic fluid acting upon the spool valve of the hydraulic main stage and therefore moving the spool valve between its control positions. | 08-02-2012 |