Valves of type DBW are pilot-operated pressure relief valves. They are used for limitation and solenoid-actuated unloading of the operating pressure.
The valves basically consist of housing (1) and pilot control valve (2) with adjustment type.
The pressure applied to channel P acts on the main spool (3). Via the nozzle bores (4 and 5), the pressure is at the same time applied to poppet (6). If the pressure in channel P exceeds the value set at spring (7), poppet (6) opens against spring (7). Via the nozzle bores (4 and 5), the hydraulic fluid from channel P now flows into the spring chamber (8). From here, it is led into the tank internally (version "–"), via the control line (9 and 10), or externally (version "Y") via the control line (9 and 11).
Due to the state of equilibrium at the main spool (3), hydraulic fluid flows from channel P to channel T, maintaining the set operating pressure.
A pressure gauge connection (12) allows for the control of the operating pressure.
The pressure relief valve can be unloaded or switched to another pressure (second pressure rating) via port X (13).
The main spool (3) is unloaded by controlling a built-on directional valve.