The sequence valve is a close relative of the pressure relief valve and is used where a set of operations are to be controlled in a pres sure related sequence. Figure 4.27 shows a typical example where a workpiece is pushed into position by cylinder 1 and clamped by cylinder 2.
Sequence valve V2 is connected to the extend line of cylinder 1. When this cylinder is moving the workpiece, the line pressure is low, but rises once the workpiece hits the end stop. The sequence valve opens once its inlet pressure rises above a preset level.
Cylinder 2 then operates to clamp the workpiece. A check valve across V2 allows both cylinders to retract together.