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MAIN HYDRAULIC SYSTEMS -RETURN FILTER MODULES
A red indicator on the bypass relief valve extends to show the bypass valve is open.
You use the ground service disconnect as the return port during ground hydraulic pressure cart operation. The center system ground service disconnect is not on the return filter module. A hydraulic tube connects the disconnect to the module.
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MAIN HYDRAULIC SYSTEMS -RETURN FILTER MODULES
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MAIN HYDRAULIC SYSTEMS -HEAT EXCHANGERS
Purpose
A heat exchanger in each hydraulic system cools the case drain hydraulic fluid from the EDPs and the ACMPs. This extends the service life of the fluid and the hydraulic pumps.
Physical Description
The heat exchangers use aluminum finned tubes to transfer heat from the fluid to the fuel. Fuel in the left and right main tanks cools the hydraulic fluid.
Location
The heat exchanger for the left hydraulic system is in the left main fuel tank between ribs 10 and 11.
The heat exchangers for the right hydraulic system is in the right main fuel tank between ribs 10 and 11.
The heat exchangers for the center hydraulic system is in the right main fuel tank between ribs 11 and 12.
Training Information Point
NOTE: The heat exchangers in the hydraulic system use the fuel to remove heat from the hydraulic system.
Approximately 709 gallons (2688 liters) (4794 pounds) (2175 kg) of fuel in the left and right main fuel tanks is necessary to cool the case drain flow from the left and right hydraulic systems.
Approximately 1080 gallons (4095 liters) (7303 pounds) (3313 kg) of fuel in the right main tank is necessary to cool the case drain flow from the center hydraulic system.
You can operate the hydraulic pumps if fuel goes below these levels if you obey the CAUTION below.
CAUTION: DO NOT OPERATE THE HYDRAULIC PUMPS AFTER THE HYDRAULIC TEMPERATURE INDICATION IS MORE THAN 100C (212F) OR AFTER THE PUMP FAULT LIGHT COMES ON. IF YOU CONTINUE TO OPERATE THE PUMPS, THE HYDRAULIC FLUID CAN BECOME TOO HOT.
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777 AIRCRAFT MAINTENANCE MANUAL
MAIN HYDRAULIC SYSTEMS -HEAT EXCHANGERS
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MAIN HYDRAULIC SYSTEMS -RESERVE ISOLATION VALVE AND NOSE GEAR ISOLATION VALVE
General The reserve isolation valve and the nose gear isolation valve supply engine burst protection to the center hydraulic system to prevent complete loss of center system fluid. Location Both valves are in the right wheel well on the keelbeam.
These valves permit a reserve brake and nose gear steering operation if there is a leak in the PFCS or MLG hydraulic lines. The valves also permit PFCS and MLG operation if there is a leak in the NLG or LE slat hydraulic lines.
The reserve isolation valve and the nose gear isolation valve are part of the center hydraulic isolation system (CHIS).
The reserve isolation valve isolates brakes and steering from the center hydraulic system.
The nose gear isolation valve controls ACMP C1 output to nose gear steering. Physical Description The reserve isolation valve and nose gear isolation valves are the same.
They are 28v dc motor-powered, two-position valves. They each have a position indication lever which permits you to manually operate the valve.
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MAIN HYDRAULIC SYSTEMS -RESERVE ISOLATION VALVE AND NOSE GEAR ISOLATION VALVE
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MAIN HYDRAULIC SYSTEMS -CENTER SYSTEM RETURN MANIFOLD AND PRESSURE RELIEF VALVE
Return Manifold
The center system return manifold collects the return hydraulic flows from center hydraulic system components.
The manifold is on the ceiling in the right wheel well near the keelbeam.
Pressure Relief Valve
A center system pressure relief valve supplies overpressure protection to the part of the center system that may be isolated by the CHIS.
The relief valve is on the keelbeam in the right wheel well.
The relief valve starts to open at a pressure of 3700 -3900 psid.
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