Figure 10.4 depicts a circuit used for unloading a pump using an unloading valve.
In this circuit, the unloading valve opens as the cylinder reaches the end of its extension stroke. This is because the check valve keeps the high-pressure oil in the pilot line of the unloading valve. When the DCV is shifted to retract the cylinder, the motion of the cylinder reduces the pressure in the pilot line of the unloading valve. This resets the unloading valve until the cylinder is fully retracted at the point where the unloading valve unloads the pump. It is thus seen that the unloading valve unloads the pump at the end of the extending and retracting strokes as well as in the spring-centered position of the DCV.