Sun sequence cartridges are normally closed pressure control elements designed to modulate flow from port 1 (inlet) to port 2 (outlet) (like a relief valve) as long as the pressure at port 1 exceeds the pressure setting plus the back pressure at port 3 (the control chamber drain). Unlike relief valves, sequence valves generate a constant pressure at the inlet port irrespective of the pressure on the outlet port. When pressures at port 1 and port 2 both exceed the setting of the valve, the valve goes “full open”, or “sequences”. This function is achieved by draining the spring chamber separately to tank. Sequence valves can be used to sense pressure (port 1) in one circuit and then open and supply oil to a secondary circuit (port 2) at a predetermined pressure.