The pilot operated pressure relief valve as an unloading valve
The pilot operated pressure relief valve can also be applied as an unloading valve. Normally the 2/2-direction control valve is activated and the opening pressure of the main valve is determined by the pilot valve.
If the 2/2-direction control valve is NOT activated the pressure at the upper side of the main valve will become zero. The pressure at the bottom side of the maine valve will open the main valve: the pressure needed to do this will be about 3 bar (almost zero).
From that moment on the majority of the pumpflow will be drained towards the reservoir by the main valve.