*
Less than 180 seconds after takeoff.
The second 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 PRSOV is open
*
Left PRSOV is closed
*
Landing gear is up or 180 seconds after takeoff
*
Left engine bleed air flow is more than 2.0 lbs/sec
*
No left engine start.
Training Information Point
The ASCPC has logic that lets the left or right isolation valves stay open if the airplane has a wing or body duct leak and any of these conditions occur:
*
An engine start is in progress
*
An ADP is on and it is less than 3 minutes since the airplane has taken off.
This logic lets the engine start complete or makes sure air is available for ADP operate immediately after takeoff. If a wing or body duct leak occurs after a valve is latched close, the valve will not open for engine start or for ADP operation.
You must set the applicable bleed isolation switch to out and then AUTO to reset the related isolation valve after it latches closed. The latch will not reset if the condition that caused it is still true.
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -LEFT AND RIGHT ISOLATION VALVE CONTROL LOGIC
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -CENTER ISOLATION VALVE CONTROL LOGIC
Control Logic
The ASCPCs have control logic that sets the center isolation valve to one of these configurations:
*
Open
*
Closed
*
Latched closed.
Valve Open Control Logic
There are four sets of conditions that cause the ASCPCs to open the center isolation valve. The first set is true if all of these conditions occur:
*
C ISLN switch is set to AUTO
*
Valve latched closed logic is not true
*
Section two operation logic is not true
*
Cross bleed engine start.
The second set is true if all of these conditions occur:
*
C ISLN switch is set to AUTO
*
Valve latched closed logic is not true
*
Section two operation logic is not true
*
No duct leak signal for wing or body
*
left or right engine bleed air supply systems are off.
The third set is true if all of these conditions occur:
*
C ISLN switch is set to AUTO
*
Valve latched closed logic is not true
*
Section two operation logic is not true
*
No duct leak signal for wing or body
*
Left or right ISLN switch is set to out.
The fourth set is true if all of these conditions occur:
*
C ISLN switch is set to AUTO
*
Valve latched closed logic is not true
*
Section two operation logic is not true
*
No duct leak signal for wing or body
*
Left or right source loss.
See the duct leak and overheat detection section for more information about wing and body duct leaks (SECTION 26-18).
Section Two Operation Logic
Section two operation logic makes sure that air is not given to an air conditioning pack that is without control. Possible engine battery start condition is the primary reason for this logic. This logic is true if all of these conditions occur:
*
Both cabin temperature controllers (CTC) are off
*
One ASCPC operates in digital (primary) mode and the other ASCPC primary mode is off
*
Airplane on the ground.
Source Loss Condition Logic
The left and right 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.
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -CENTER ISOLATION VALVE CONTROL LOGIC
There are two sets of conditions that cause the ASCPCs to set the left source loss condition to true. 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
*
Left duct pressure less than 20 psig and right duct pressure more than 20 psig.
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