A Simple Hydraulic System
This animation starts off with the system depressurized. When the system is powered up, the pump starts operating, filling up the accumulator until reaching the "kick out" pressure of the relief valve. At this point, the pump becomes unloaded.

When the actuator is moved, pressure drops slightly causing the relief valve to close and allowing pump pressure back in to the system. Again, when the set point of the relief valve is reached, the pump becomes unloaded.