The primary mode is described below. See engine air supply functional description section for more information.
Bleed Port Selection
The ASCPC selects the lowest possible bleed air source while still satisfying the needs of the users systems. Selection is based on pressure, flow, altitude, air conditioning pack operation, and engine starting. The manifold pressure sensor, the intermediate pressure sensor and the EEC monitor the pneumatic duct pressure. The pneumatic duct pressure data goes to the ASCPC. If pressure goes below specified values, the ASCPC sends a command to the HPFAC. The HPFAC adjusts the position of the high pressure shutoff valve (HPSOV) so that high pressure air adds to low pressure air.
Pressure Control
The ASCPC controls the engine air supply pressure. The manifold pressure sensor and the intermediate pressure sensor monitor the pneumatic duct pressure. The pneumatic duct pressure data goes to the ASCPC. The ASCPC then sends a command to the HPFAC and the PRSOVC. The HPFAC adjusts the HPSOV and the PRSOVC adjusts the pressure regulating shutoff valve (PRSOV). The valves open and close as necessary to control the pressure.
The duct vent valve (DVV) releases high pressure to prevent overpressure indication when the engine is on and the bleed system is set to off.
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ENGINE AIR SUPPLY -GENERAL DESCRIPTION

Temperature Control

The ASCPC controls the engine air supply temperature. The manifold dual temperature sensors monitor the pneumatic duct temperature. The pneumatic duct temperature data goes to the ASCPC. The ASCPC then sends a signal to the HPFAC. The HPFAC adjusts the fan air modulating valve (FAMV) to control the temperature.
If the temperature of the bleed air gets above the usual limits, a signal goes to the PRSOVC. The PRSOVC adjusts the PRSOV as necessary to decrease the amount of hot bleed air supplied.
Flow Control

The ASCPC keeps the amount of bleed air that flows from the engine to a limit. The ASCPC uses inputs from these components or systems to monitor engine bleed airflow:
*
Manifold flow sensor (FS)

*
Engine anti-ice (EAI) system (not shown)

*
Wing anti-ice (WAI) system (not shown).

The ASCPC uses the PRSOVC to control the flow. The PRSOVC adjusts the position of the PRSOV to regulate the bleed air flow into the air supply distribution system.
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777 AIRCRAFT MAINTENANCE MANUAL

ENGINE AIR SUPPLY -GENERAL DESCRIPTION

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ENGINE AIR SUPPLY SYSTEM -ENGINE LEFT SIDE COMPONENT LOCATIONS

General

These are the engine left side components of the engine air supply system:
*
Intermediate pressure check valve (IPCV)

*
Engine duct

*
Pressure regulating and shutoff valve (PRSOV)

*
Precooler

*
High pressure shutoff valve (HPSOV).

Training Information Point

Open the left fan cowl and thrust reverser to get access to the engine air supply components.
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ENGINE AIR SUPPLY SYSTEM -ENGINE LEFT SIDE COMPONENT LOCATIONS

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ENGINE AIR SUPPLY SYSTEM -ENGINE RIGHT SIDE COMPONENT LOCATIONS

General

These are the engine right side components for the engine air supply system:
*
Duct vent valve (DVV)

*
Intermediate pressure check valve (IPCV)

*
Pressure regulating and shutoff valve controller (PRSOVC)

*
High pressure fan air controller (HPFAC).

Training Information Point

Open the right fan cowl and thrust reverser to get access to the engine air supply components.
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ENGINE AIR SUPPLY SYSTEM -ENGINE RIGHT SIDE COMPONENT LOCATIONS

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ENGINE AIR SUPPLY SYSTEM -RIGHT THRUST REVERSER COMPONENT LOCATIONS
General

The fan air modulating valve installs on ducting on the inside of the right thrust reverser.
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ENGINE AIR SUPPLY SYSTEM -RIGHT THRUST REVERSER COMPONENT LOCATIONS
　
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