5. HYDRAULIC DIAGRAM 5.6 AUXILIARY SERVICES CONTROL VALVE OPERATION 1. When the actuators are not operated a b 1 CONTROL VALVE P 2 D000 5080 When the engine is running and the driver does not operate any of the hydraulic service controls, the pump sends oil to the inlet manifold (port P ). As all the actuators are stationary, the oil pressure increases in chamber a and consequently also in chamber b . When the oil pressure in chambers a and b exceeds the force exerted by the spring (2), the spool (1) is shifted down- wards, allowing the excess oil from the pump to flow to drain. 10-51 R