[B]757 Heaven[B]
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Air Demand Pump
The center system has a bleed air dirven hydraulic pump which provides hydtaulic power. The air demand pump selector determins the pump mode of operation. In the Auto postion, the air pump operates whenever system pressure is low or when large demand systems such as landing gear flaps/slats and ground spoilers are operated. In the On position, the pump runs continuously.
The Hydraulic Driven Generator is automatically powered by the center hydrautic system when electrical power is lost from both main AC busses. The center Air Demand Pump will then operate continuously to ensure sufficient power to drive the generator.