Bosch Rexroth R901311438

Valves of type DRE(M)E are pilot-operated pressure reducing valves. They are used for operating pressure reduction. These valves basically consist of a pilot control valve (1) with proportional solenoid (2), a main valve (3) with main spool insert (4), as well as an optional check valve (5). On the proportional solenoid, there is moreover a housing (15) with the control electronics. Supply and command value voltage are applied at the connector (16). At the factory, the command value pressure characteristic curve is adjusted with little manufacturing tolerance. Type DREE... The pressure in channel A is set in a command value-dependent form via the proportional solenoid (2). In rest position – no pressure in channel B –, the spring (11) holds the main spool (4) in its initial position. The connection from channel B to A is open. The pressure in channel A acts on the bottom side of the main spool in closing direction, and the pressure of the pilot control valve on the spring side of the main spool in the opening direction from channel B to A. The pilot oil is taken from channel B and flows through the bore (6) to the constant-current control (9) which keeps the pilot flow constant independent of the pressure drop between channel A and B. From the constant-current control (9), the pilot flow flows through the bores (7) via the valve seat (10), passes the valve poppet (8) and is directed into channel Y to the tank. The pressure required in channel A is preset at the related amplifier. The proportional solenoid pushes the valve poppet (8) in the direction of the valve seat (10) and limits the pressure in the spring chamber (12) to the set value. In the control position of the main spool (4), the hydraulic fluid flows from channel B to A and generates the pressure in channel A (setting of the pilot control valve plus spring (11)). If the set pressure in A is achieved, the forces at the main spool are balanced. If the actuator at port A does not move (e. g. cylinder piston at stop) and a lower pressure is set for channel A via the proportional solenoid (2), the main spool (4) closes the connection from B to A and simultaneously opens the connection from channel A to the spring chamber (12) of the main spool (4). In this position, the compression volume in channel A can expand via the pilot control valve (1) and port Y. For the free flow back from channel A to B, a check valve (5) can optionally be installed. A pressure gauge connection (13) allows for the control of the reduced pressure in channel A. Type DREME... For hydraulic protection against an inadmissibly high electric control current at the proportional solenoid, which imperatively results in excessive pressures in port A, you can optionally install a spring-loaded pressure relief valve as maximum pressure limitation (14). The maximum pressure limitation is pre-set based on the relevant pressure rating.