HYDRAULIC POWER
Hydraulic power is supplied by 2 independent systems: left and right. Each has a reservoir and a single engine-driven pump. The two systems are similar except for equipment being powered.
The left system supplies pressure to the left engine thrust reverser, left and right inboard flight spoilers, and the elevator augmentor. The right system supplies pressure to the right engine thrust reverser, left and right outboard flight spoilers, rudder, landing gear, and the aft stairs. Both systems supply pressure to leading edge slats, flaps, ground spoilers, nosewheel steering, brakes, and anti-skid.
Backup hydraulic system pressure is provided by an electric auxiliary pump and a transfer hydraulic pump. Fluid cannot transfer from one side to the other, but one system can provide pressure to the other with the transfer hydraulic pump.
Pulling the left or right fire control handle closes a fire shutoff valve that shuts off fluid to the corresponding engine-driven pump.
RESERVOIRS
Left and right hydraulic
fluid quantity indicators on the hydraulic
panel that is on the first officers panel (center instrument panel on the GLASS
panel) and display readings from the quantity transmitters in each
reservoir.
SYSTEM PUMPS
Switches on the hydraulic panel (main panel on the GLASS panel) control the engine-driven pumps. These switches have HI, LOW, and OFF positions. In HI, the pump provides 3,000 psi; in LOW, it provides 1,500 psi; in off the pump provides zero pressure but remains lubricated. Indicators above the control switches (on the center instrument panel on the GLASS panel) display left and right system pressure.
L (or R) HYD PRESS LOW annunciation indicates low pressure in the associated spoiler system supply line. Pressure is sensed downstream of the spoiler shutoff valve.
AUXILIARY PUMP
An electric auxiliary pump in the right system provides a backup source of right system pressure. Power for the auxiliary pump is provided by the Left AC bus. With no engine pumps operating, the AUX pump and transfer pump will pressurize both hydraulic systems. If the axiliary pump overheats, it will shut down automatically.
A switch with ON, OFF and OVRD positions on the hydraulic panel controls the auxiliary pump. In ON, the auxiliary pump provides 3,000 psi. Holding the switch in the momentary OVRD position bypasses the overheat protection circuit, allowing continuous pump operation.
TRANSFER HYDRAULIC PUMP
The transfer hydraulic pump is a motor/pump combination connecting the left and right hydraulic systems. When operating, it transfers hydraulic pressure from the system with higher pressure to the system with lower pressure. An ON/OFF switch on the hydraulic control panel controls the pump. The transfer pump is guarded to the OFF position.
The transfer pump control has a single motor that operates two shutoff valves, one in each hydraulic system. When the pump is on, the valves open, supplying fluid from the left and right systems to both sides of the pump. The high pressure side of the pump operates as a motor, turning the low pressure side which operates as a pump. Some loss of pressure is normal on the low pressure side.
HYDRAULIC POWER SYSTEM
STEAM & COMBO
LOCATION:
Hydraulic Panel
GLASS
LOCATION: Main Panel
HYDRAULIC PUMP SWITCHES
HI - Pump provides 3,000 psi.
LOW - Pump provides 1,500 psi.
OFF - Pump depressurised, no pressure output. Lubrication and cooling only.
TRANSFER PUMP SWITCH
ON - Mechanically connects left and right hydraulic systems.
OFF - Separates left and right hydraulic systems.
HYDRAULIC PRESSURE INDICATORS
Multiply by 1,000 to get pressure.
AUXILIARY PUMP SWITCH
ON - Pump provides 3,000 psi.
OFF - Pump not operating.
OVRD - Momentary. Provides 3,000 psi, by by-passing overheat protection circuit.
HYDRAULIC QUANTITY LOW LIGHTS
Indicate hydraulic quantity below minimum level.
- Indicates system pressure low in associated spoiler system supply line.
- Indicates hydraulic reservoir fluid temperature above normal.