There are two sets of conditions that cause the ASCPCs to set the right 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
*
Right engine off.
The second set is true if all of these conditions occur:
*
Landing gear down
*
Less than 180 seconds since takeoff
*
Right duct pressure less than 20 psig and left duct pressure more than 20 psig.
Valve Closed Control Logic
There are four sets of conditions that cause the ASCPCs to set the center isolation valve to close. The first set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
C ISLN switch is set to out.
The second set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
Section two operation logic is true.
The third set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
L or R source loss logic is not true
*
Cross bleed engine start logic is not true
*
L and R PRSOVs open
*
L and R engine bleed switch set to ON
*
L and R engines are on
*
L and R ISLN switches set to AUTO.
The fourth set is true if all of these conditions occur:
*
Valve latched closed logic is not true
*
ASCPC looking for the location of wing or body duct leak but not during a cross bleed engine start.
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -CENTER ISOLATION VALVE CONTROL LOGIC
If the engine cross bleed start condition is not true, the ASCPCs close the valve when they use it 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 its usual position. If the ASCPCs find that the valve does effect the leak, the valve is latched close.
Valve Latched Closed Control Logic
The center isolation valve is latched closed to isolate a section of duct that has a leak. The valve is latched closed if there is a body or inboard (L or R) wing duct leak.
When a duct leak condition occurs, the ASCPCs latch the valve close after the location of the leak is known or after a specified quantity of time. These are examples of the time permitted to find the location of a leak:
*
Wing leak, 185 seconds
*
Body leak, 95 seconds.
Training Information Point
The ASCPC has logic that lets the center isolation valve 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 three 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 the valve is latched close, the valve will not open for engine start or for ADP operation.
You must set the center bleed isolation switch to OUT and then AUTO to reset the center isolation valve after it latches closed. The latch will not reset if the condition that caused it is still true.
EFFECTIVITY BEJ ALL 36-12-00
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -CENTER ISOLATION VALVE CONTROL LOGIC
EFFECTIVITY BEJ ALL 36-12-00
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D633W101-BEJ May 05/2002
AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -APU SHUTOFF VALVE CONTROL LOGIC
Control Logic
The ASCPCs have control logic that sets the APU shutoff valve (APUSOV) to one of these configurations:
*
Open
*
Closed
*
Latched closed.
Valve Open Control Logic
There are five sets of conditions that cause the ASCPCs to open the APUSOV. The first set relates to APU autostart logic for when the airplane operates on standby power. This set is true if all of these conditions occur:
*
APU fire switch is set to in
*
APU bleed switch is set to AUTO
*
Power is off the left and right transfer buses
*
Airplane is in the air
*
APU is off.
See the ignition/starting section for more information on APU autostart (SECTION 49-40).
The second set relates to cooldown for the solenoid on the APUSOV. Hot solenoid cooldown logic removes power when it is not necessary to set the valve to close. This second set is true if all of these conditions occur:
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