DISTRIBUTION SYSTEMS - PRIMARY HYDRAULIC POWER SYSTEM BASIC PRINCIPLES OF THE SYSTEM Pilot Operated Hydraulic System 1. Pilot-operated hydraulic system has two basic parts or sections: A pilot (also called primary) section, and a main (also called secondary) section. 2. When a pilot-operated system is actuated, the pilot (primary) always moves first. Once the pilot has operated, the main (secondary) section always moves last. This is true whether the system is being activated or deactivated. 3. The movement of the pilot (primary) controls a very small amount of oil flow (pilot flow).
The movement of the main (secondary) controls the majority of the oil flow (main flow) and is responsible for actuating a given system. The header raise/header lower and reel drive valve are three examples of a pilot operated system used on the combine. A.10.A / 6