The function of the main hydraulic power-system is to supply hydraulic pressure to different systems on the aircraft.

The main hydraulic system has the systems that follow:

Flight-Compartment Control System

The flight-compartment control system contains the HYDRAULIC control panel. The HYDRAULIC control panel is installed in the flight compartment on the overhead panel. Also, the engine indication and crew alerting system (EICAS) monitors the hydraulic system.

No. 1 and No. 2 Hydraulic Systems

The No. 1 and No. 2 hydraulic systems supply hydraulic fluid of correct pressure, temperature and quantity to the systems that operate with hydraulic pressure. The engine driven pumps (EDP) 1A and 2A supply the primary pressure. More hydraulic pressure is supplied, as necessary, by the AC-motor-driven pumps (ACMP) 1B and 2B. The ACMPs are secondary pumps if the EDPs are defective. If there is an engine fire, the firewall hydraulic shutoff-valve is closed when the fire extinguisher handles are pulled. This stops the flow of hydraulic fluid to and from the EDPs.

No. 3 Hydraulic System

The No. 3 hydraulic system supplies and controls the hydraulic fluid of the correct pressure, temperature and quantity to the systems that operate with hydraulic pressure. The primary pressure for the No. 3 hydraulic system comes from the continuous operation of the ACMP 3A. More hydraulic pressure is supplied, if necessary, by the ACMP 3B. ACMP 3B is a secondary pump, if the ACMP 3A is defective. In an emergency, when ACMP 3A and 3B are defective, the RAM Air Turbine will supply hydraulic pressure to the No. 3 hydraulic system.

Hydraulic Fluid Heating-System

Each of the three hydraulic systems (No. 1, No. 2 and No. 3) has a hydraulic fluid-heating system. The fluid heating system supplies the secondary ACMPs (1B, 2B and 3B) with a constant flow of warm fluid. This warm fluid goes through the pumps. Restrictor-check valves control the fluid flow. This helps ACMP starts, because of cold temperatures and long stopped periods.

Quick Disconnects

No. 1, No. 2 and No. 3 hydraulic systems, each have quick disconnect couplings in the ground fill, return and pressure circuits. They are used for ground servicing and general maintenance tasks. The quick disconnects are installed near the filter manifolds for each hydraulic system.

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