DB,DBW Pressure valves are pilot operated pressure relief valves
They are used for the limitation (DB) or limitation and solenoid actuated unloading (DBW) of the operating pressure. The pressure relief valves (DB) consistmainly of the main valve (1) with the spool assembly (3) and pilot valve (2) with pressure adjustment element。

Pressure relief valve type BD
The pressure presentin pilot A acts on the main spool (3).，At the same time pressure is present via the control line (6) and (7), which are fitted with orifices (4) and (5) on the spring loaded side of side main spool (3) and at the ball (8) in the pilot valve (2). if  the pressure in port A exceeds the valve set at the spring (9) the ball (8) open s against the spring (9).

The signal for this comes intemaily via the control lines (10) and (6) from port A. The pressure fluid on the spring loaded side of the main poppet (3) now flows via the control line (7), orifice bore (11) and ball (8) into the spring chamber (12). In Type DB..-5X/..-. it  flow s intemaily via the control line (13) to tank, or, in type DB..5X/..Y.. extemaily via the control line (14). Due to the orifices (4) and (5) a pressure drop occurs at main spool (3),the connection from port A to port B is open. Now the pressure fluid flows from port A to port B whilst.

The pressure relief valve may be unloaded or switched over to a different pressure (second pressure stage) via port "X" (15).