A sequencing valve again is a normally closed pressure control valve used for ensuring a sequential operation in a hydraulic circuit, based on pressure. In other words, sequencing valves ensure the occurrence of one operation before the other. A sectional view of a sequencing valve is shown in Figure 6.23.
When the components connected to port A of the valve reach the pressure set on the valve, the fluid is passed by the valve through port B to do additional work in a different portion of the system. The high-flow poppet of the sequence valve is controlled by the spring-loaded cone. At low pressures, the poppet blocks the flow of fluid from entering port A. The pressure signal at port A passes through the orifices to the top side of the poppet and to the cone. There is no flow through the valve unless the pressure at port A exceeds the maximum set pressure on the spring-loaded cone. When the pressure reaches the set valve, the main poppet Hfts, allowing the flow to pass through port B. It maintains the adjusted pressure at port A until the pressure at port B rises to the same value. A small pilot flow (about VA gpm) goes through the control piston and past the pilot cone to the external drain. When there is subsequent pressure increase in port B, the control piston acts to prevent further pilot flow loss. The main poppet opens fully and allows the pressures at port A and B to rise together. Flow may go either way during this condition.