*
Valve latched closed logic is not true.
The second set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
L ISLN switch is set to AUTO
*
No duct leak signal for Left (strut, wing, or body)
*
No left source loss
*
Center isolation valve operates correctly (right isolation valve logic only)
*
Left engine start.
The third set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
L ISLN switch is set to AUTO
*
Cross bleed engine start.
See the duct leak and overheat detection system section for more information about strut, wing, and body leaks (SECTION 26-18).
Source Loss Condition Logic
The source loss condition logic lets the ASCPCs sense when there is not sufficient air pressure to the ADPs for landing gear retraction, immediately after takeoff.
Source loss can occur in the left or right parts of the pneumatic distribution system. There are two sets of conditions that cause the ASCPCs to set the left source loss condition to true. The conditions that cause the right source loss condition are equivalent to left. The first set is true if all of these conditions occur:
*
Landing gear down
*
Less than 180 seconds since takeoff
*
Left engine off.
The second set is true if all of these conditions occur:
*
Landing gear down
*
Less than 180 seconds since takeoff
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -LEFT AND RIGHT ISOLATION VALVE CONTROL LOGIC
* Left duct pressure less than 20 psig and right duct pressure more than 20 psig.
Center Isolation Valve Operates Correctly Logic
Control logic for the right isolation valve monitors the center isolation valve. If the center valve fails open, the right isolation valve closes as necessary to isolate the left the right engine bleed air supply systems.
Valve Closed Control Logic
The ASCPCs set the valve to close if the valve latched close logic is not true and any of these conditions occur:
*
Left bleed isolation switch set to out
*
Right engine start and not left engine start
*
Left source loss
*
Center isolation valve open when it should be closed (right isolation valve logic only).
If an engine cross bleed start condition is not true, the ASCPCs also close the valve when they use the valve to find the location of a duct leak. If the ASCPCs find that the valve has no effect on the leak, the valve is set to open. If the ASCPCs find that the valve does effect the leak, the valve is latched close.
Valve Latched Close Control Logic
The left isolation valve latches closed to isolate a section of duct that has a leak or pressure less than it should be for the airplane conditions. The valve is latched closed if any of these conditions occur:
*
The ASCPCs identify the location of a Left strut, left wing or left body duct leak
*
The ASCPCs fail to identify the location of a duct leak after a specified quantity of time
*
Left bleed pressure loss.
When a duct leak condition occurs, the ASCPCs latch the valve closed only after the location of the leak is known or after a specified quantity of time. These are examples of the quantity of time permitted to find the location of a leak:
*
Strut leak -5 seconds
*
Wing leak -185 seconds
*
Body leak -95 seconds.
Bleed Pressure Loss Condition Logic
The bleed pressure loss condition logic lets the ASCPCs sense when a pneumatic duct breaks. Possible engine starter duct failure is the primary reason for this logic.
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -LEFT AND RIGHT ISOLATION VALVE CONTROL LOGIC
There are two sets of conditions that cause the ASCPCs to set the left bleed pressure loss condition to true. The conditions for a right bleed pressure loss condition are equivalent to the left. The first set is true if all of these conditions occur for more than 10 seconds:
*
Left duct pressure is less than 13 psig
*
Left pack inlet pressure is less than 13 psig
*
Right duct pressure is more than 13 psig
*
Left PRSOV is open
*
Right PRSOV is open
*
No duct leak signal from the duct leak and overheat detection system (DLODS)
* 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 气源 Pneumatic(26)
