The ACMP temperature switch is wired in parallel with the ACMP case drain temperature transducer. When the temperature switch closes, it simulates a high temperature signal by connecting a fixed resistance to the ACMP temperature transducer input on the HYDIM card.
BEJ ALL
See the hydraulic temperature indicating section for more information ().
Pressure Relief
Pressure relief valves in each ADP filter module prevent system overpressurization. A pressure relief valve near ACMP C1 supplies overpressure protection for the CHIS.
EFFECTIVITY BEJ ALL 29-10-00
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MAIN HYDRAULIC SYSTEMS -CENTER SYSTEM -FUNCTIONAL DESCRIPTION
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EFFECTIVITY BEJ ALL POST SB 777-29-0024 29-10-00
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MAIN HYDRAULIC SYSTEMS -CENTER HYDRAULIC ISOLATION SYSTEM -FUNCTIONAL DESCRIPTION
General
The center hydraulic isolation system (CHIS) supplies engine burst protection and a reserve brakes and steering function.
The HYDIM CL card, in the left systems card file, automatically controls CHIS operation through relays in the ELMS. The relays control the electric motors in the reserve and nose gear isolation valves.
HYDIM CL also sends a signal to the FSEUs to prevent hydraulic operation of the leading edge slats.
Hydraulic Supply
ACMP C1 gets hydraulic fluid from the bottom of the center system reservoir. All other hydraulic pumps in the center system get fluid through a standpipe in the reservoir. This gives ACMP C1 a 1.2 gallon (4.5 liter) reserve supply of hydraulic fluid.
Isolation
The reserve and nose gear isolation valves are normally open.
Both valves close if the quantity in the center system reservoir is low (less than 0.40) and the airspeed is more than 60 knots for more than one second. The HYDIM CL card also sends a signal to the FSEUs. The FSEUs do not send commands to the leading edge slats primary control valve (PCV) for this condition. This prevents hydraulic operation of the slats.
EFFECTIVITY
BEJ ALL
When CHIS is active, this divides the center hydraulic system into different parts. The NLG actuation and steering, and the leading edge slat hydraulic lines are isolated from center system pressure.
The output of ACMP C1 goes only to the alternate brake system.
The output of the other center hydraulic system pumps goes to the trailing edge flaps, the MLG actuation and steering and the PFCS.
If there is a leak in the NLG actuation and steering or LE slat lines, there is no further loss of hydraulic fluid. The alternate brakes, the trailing edge flaps, the MLG actuation and steering, and the PFCS continue to operate normally.
If there is a leak in the trailing edge flaps, the MLG actuation and steering, or the PFCS lines, the reservoir loses fluid down to the standpipe level (0.00 indication). This causes a loss of these systems. But, the alternate brake system continues to get hydraulic power from ACMP C1.
If there is a leak in the lines between ACMP C1 and the alternate brake system, all center hydraulic system fluid is lost.
Nose Gear Isolation Valve
The HYDIM CL reopens the nose gear isolation valve for any of these conditions:
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MAIN HYDRAULIC SYSTEMS -CENTER HYDRAULIC ISOLATION SYSTEM -FUNCTIONAL DESCRIPTION
*
Airspeed is less than 60 knots
*
Pump pressures for ACMP C2, ADP C1, ADP C2, and the RAT is less than 1200 psi for 30 seconds
*
Left and right engine RPM is above idle, left and right EDP pressure is more than 2400 psi, and (the NLG is not up, the NLG doors are not closed, or the landing gear lever is not up) for 30 seconds.
The first condition permits the flight crew to operate the NLG steering when airspeed is less than 60 kts (decreased rudder control authority during taxi).
The second condition permits operation of the NLG actuation and steering if the hydraulic leak is in the part of the center hydraulic system isolated by the reserve isolation valve.
The third condition permits operation of the NLG actuation and steering if there has not been an engine burst and the other hydraulic systems are pressurized. The nose gear isolation valve opens when pressure is necessary at the NLG. If the NLG is not fully retracted or the NLG doors are not closed, the nose gear isolation valve opens to let the NLG complete the retraction. When the landing gear lever is moved to the DOWN position, the nose gear isolation valve opens to let the NLG extend with center system pressure.
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