Low PressureHigh PressureVacuum PressureDrain PressureColors LegendMedium PressureSystem 1ABValve 1PTSystem 2ABABValve 3Valve 2TPSystem 3: Closed Center SystemABABValve 5Valve 4TPQminQmaxSystem 4: Open Center SystemABABValve 7Valve 6TPPlug removedfrom closedcenter system