* HPSOV clamp logic (HPSOV).
The primary mode latches the PRSOV and the HPSOV close if any of these conditions occur:
*
Engine strut duct leak
*
Wing duct leak
*
Engine bleed overtemperature, 490F (254C)
*
Engine bleed overpressure, 242.5 psig
*
PRSOV failed closed
*
Bleed pressure loss.
When the PRSOV is set to close or latched close, these indications show in the flight deck:
*
OFF light (not shown) in the related engine bleed switch
*
ENG BLEED OFF L (R) advisory message (not shown).
When the engine bleed switch is set to the in (ON) position, the primary mode commands the HPSOV and the PRSOV to regulate to a setpoint. The FAMV is usually set towards closed.
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 first set is true if all of these conditions occur:
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*
Landing gear is down
*
Less than 180 seconds since takeoff
*
Left engine is off.
The second set is true if all of these conditions occur:
*
Landing gear is down
*
Less than 180 seconds since takeoff
*
Left duct pressure is less than 20 psig and right duct pressure is more than 20 psig.
The conditions that cause a right source loss are equivalent.
See the distribution section for more information about the configuration of the pneumatic distribution system during source loss (SECTION 36-20).
Bleed Pressure Loss Condition Logic
The bleed pressure loss condition logic lets the ASCPCs sense when a pneumatic duct breaks. Engine starter duct failure is the primary reason for this logic.
There are two sets of conditions that cause the ASCPCs to set the left bleed pressure loss condition to true. 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
EFFECTIVITY
BEJ ALL
*
Left PRSOV is open
*
Right PRSOV is open
*
No duct leak signal from the duct leak and overheat detection system (DLODS)
*
Landing gear is up
*
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 more than 180 seconds after takeoff
*
Left engine bleed air flow is more than 2.0 lbs/sec
*
No left engine start.
The conditions that cause a right bleed pressure loss are equivalent.
See the distribution section for more information about the configuration of the pneumatic distribution system during bleed pressure loss (SECTION 36-20).
On/Off Control -Backup Mode
The backup mode provides on/off control differently from the primary mode. The backup mode only sets the PRSOV to open or close. It does not control the position of the HPSOV or the FAMV.
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The backup mode sets the PRSOV to closed for the applicable engine if any of these conditions occur:
*
Engine bleed air switch set to out
*
Engine fire switch set to out (pulled)
*
Engine start selected
*
Engine is off.
The backup mode latches the PRSOV closed if any of these conditions occur:
*
Engine strut duct leak
*
Engine bleed overtemperature, 490F (254C)
*
Engine bleed overpressure, 242.5 psig.
The backup mode gives the same flight deck indications as the primary mode when the PRSOV is set to close or latched closed.
Bleed Source Selection -Primary Mode
The bleed source selection function makes sure there is sufficient pressure downstream of the HPSOV for the systems that use engine bleed air. This is the same as the logic for the pressure regulation function. 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(18)
