DOC AIRBUS | AMM A320FBLEED AND SURGE AIR - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The APU load compressor supplies the APU bleed air. The quantity changes with the different bleed air demands of the pneumatic systems. Variable Inlet Guide Vanes (IGVs) (which are installed at the load compressor inlet) control the quantity of the bleed air.
An APU load control valve and a surge control valve are installed on the outlet orifices of the bleed air T-duct. The APU load control valve stops or permits the bleed air flow from the APU to the pneumatic system of the aircraft. The surge control valve prevents a load compressor surge. The excess air passes through the valve to the exhaust cone.
The Electronic Control Box (ECB) 59KD controls and monitors the APU bleed air supply and the surge air flow. You start and stop the bleed air supply with the APU BLEED pushbutton switch, which is on the AIR overhead panel 30VU in the cockpit.
** ON A/C NOT FOR ALL The APU load compressor supplies the APU bleed air. The quantity changes with the different bleed air demands of the pneumatic systems. Variable Inlet Guide Vanes (IGVs) (which are installed at the load compressor inlet) control the quantity of the bleed air.
An APU load control valve and a surge control valve are installed on the outlet orifices of the bleed air T-duct. The APU load control valve stops or permits the bleed air flow from the APU to the pneumatic system of the aircraft. The surge control valve prevents a load compressor surge. The excess air passes through the valve to the exhaust cone.
The Electronic Control Box (ECB) 59KD controls and monitors the APU bleed air supply and the surge air flow. You start and stop the bleed air supply with the APU BLEED pushbutton switch, which is on the AIR overhead panel 30VU in the cockpit.
2. Component Location
** ON A/C NOT FOR ALL 
Bleed and Surge Air - Component Location| ------------------------------------------------------------------------------- |
| FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA |
| | | | | DOOR | REF. |
| ------------------------------------------------------------------------------- |
| PROBE - TOTAL PRESSURE 316 316AR 49-51-14 |
| TRANSDUCER - DIFFERENTIAL PRESSURE 316 316AR 49-51-16 |
| SENSOR TRANSDUCER - TOTAL PRESSURE 316 316AR 49-51-17 |
| SENSOR TRANSDUCER - APU INLET PRESSURE 316 316AR 49-51-20 |
| VALVE - LOAD CONTROL 316 316AR 49-51-51 |
| VALVE - SURGE CONTROL 316 316AR 49-51-52 |
A. Primary Components
The bleed and surge air system has the primary components:
The bleed and surge air system has the primary components:
- a total pressure probe,
- static pressure probe,
- a total pressure transducer,
- a differential pressure transducer,
- a APU inlet pressure transducer,
- a load control valve,
- a surge control valve.
B. Bleed Air
The APU bleed air is supplied to the aircraft pneumatic system from the APU load compressor via the tee-duct and the load valve.
The Load Control Valve (LCV) is installed at the forward end of the tee-duct and forms the interface to the aircraft pneumatic system. It is a simple CLOSED/OPEN butterfly valve and therefore not able to regulate the quantity of bleed air flow. It permits or stops the bleed air flow from the APU to the aircraft users.
The LCV is normally spring-loaded closed and uses load-compressor bleed-air, controlled by a valve-mounted solenoid, to provide the force for valve opening. The ECB controls and monitors the LCV position.
When the ECB receives an APU bleed demand signal it commands the solenoid of the LCV to open the valve. Two switches (full open/full closed) within the LCV transmit position feedback signals to the ECB. A position indicator on the valve shaft gives additional visual information of the LCV position.
The different quantity of APU bleed air flow is depending of the aircraft pneumatic system demands like:
The IGVs are moved by the Inlet Guide Vane Actuator (IGVA), which uses fuel hydraulic power to position the IGVs.
The IGV position is computed by the ECB, primarily based on
The ECB controls the operation of the IGVA by adjusting the current of a torque motor inside the IGVA. The torque motor operation regulates the hydraulic extraction/retraction of the IGVA piston. The correct position of the IGVs is monitored by the ECB, using an analogue voltage signal, supplied by a Linear-Voltage Differential Transducer (LVDT) within the IGVA. This voltage signal has a linear relationship to the IGV position.
The APU bleed air is supplied to the aircraft pneumatic system from the APU load compressor via the tee-duct and the load valve.
The Load Control Valve (LCV) is installed at the forward end of the tee-duct and forms the interface to the aircraft pneumatic system. It is a simple CLOSED/OPEN butterfly valve and therefore not able to regulate the quantity of bleed air flow. It permits or stops the bleed air flow from the APU to the aircraft users.
The LCV is normally spring-loaded closed and uses load-compressor bleed-air, controlled by a valve-mounted solenoid, to provide the force for valve opening. The ECB controls and monitors the LCV position.
When the ECB receives an APU bleed demand signal it commands the solenoid of the LCV to open the valve. Two switches (full open/full closed) within the LCV transmit position feedback signals to the ECB. A position indicator on the valve shaft gives additional visual information of the LCV position.
The different quantity of APU bleed air flow is depending of the aircraft pneumatic system demands like:
The IGVs are moved by the Inlet Guide Vane Actuator (IGVA), which uses fuel hydraulic power to position the IGVs.
The IGV position is computed by the ECB, primarily based on
The ECB controls the operation of the IGVA by adjusting the current of a torque motor inside the IGVA. The torque motor operation regulates the hydraulic extraction/retraction of the IGVA piston. The correct position of the IGVs is monitored by the ECB, using an analogue voltage signal, supplied by a Linear-Voltage Differential Transducer (LVDT) within the IGVA. This voltage signal has a linear relationship to the IGV position.
The APU bleed air is supplied to the aircraft pneumatic system from the APU load compressor via the tee-duct and the load valve.
The Load Control Valve (LCV) is installed at the forward end of the tee-duct and forms the interface to the aircraft pneumatic system. It is a simple CLOSED/OPEN butterfly valve and therefore not able to regulate the quantity of bleed air flow. It permits or stops the bleed air flow from the APU to the aircraft users.
The LCV is normally spring-loaded closed and uses load-compressor bleed-air, controlled by a valve-mounted solenoid, to provide the force for valve opening. The ECB controls and monitors the LCV position.
When the ECB receives an APU bleed demand signal it commands the solenoid of the LCV to open the valve. Two switches (full open/full closed) within the LCV transmit position feedback signals to the ECB. A position indicator on the valve shaft gives additional visual information of the LCV position.
The different quantity of APU bleed air flow is depending of the aircraft pneumatic system demands like:
- MES
- ECS,
The IGVs are moved by the Inlet Guide Vane Actuator (IGVA), which uses fuel hydraulic power to position the IGVs.
The IGV position is computed by the ECB, primarily based on
- aircraft bleed demand (i.e. MES, ECS),
- ambient temperature (T2),
- and the inlet pressure (P2).
The ECB controls the operation of the IGVA by adjusting the current of a torque motor inside the IGVA. The torque motor operation regulates the hydraulic extraction/retraction of the IGVA piston. The correct position of the IGVs is monitored by the ECB, using an analogue voltage signal, supplied by a Linear-Voltage Differential Transducer (LVDT) within the IGVA. This voltage signal has a linear relationship to the IGV position.
The APU bleed air is supplied to the aircraft pneumatic system from the APU load compressor via the tee-duct and the load valve.
The Load Control Valve (LCV) is installed at the forward end of the tee-duct and forms the interface to the aircraft pneumatic system. It is a simple CLOSED/OPEN butterfly valve and therefore not able to regulate the quantity of bleed air flow. It permits or stops the bleed air flow from the APU to the aircraft users.
The LCV is normally spring-loaded closed and uses load-compressor bleed-air, controlled by a valve-mounted solenoid, to provide the force for valve opening. The ECB controls and monitors the LCV position.
When the ECB receives an APU bleed demand signal it commands the solenoid of the LCV to open the valve. Two switches (full open/full closed) within the LCV transmit position feedback signals to the ECB. A position indicator on the valve shaft gives additional visual information of the LCV position.
The different quantity of APU bleed air flow is depending of the aircraft pneumatic system demands like:
- MES
- ECS,
- iCARE.
The IGVs are moved by the Inlet Guide Vane Actuator (IGVA), which uses fuel hydraulic power to position the IGVs.
The IGV position is computed by the ECB, primarily based on
- aircraft bleed demand (i.e. MES, ECS, iCARE),
- ambient temperature (T2),
- and the inlet pressure (P2).
The ECB controls the operation of the IGVA by adjusting the current of a torque motor inside the IGVA. The torque motor operation regulates the hydraulic extraction/retraction of the IGVA piston. The correct position of the IGVs is monitored by the ECB, using an analogue voltage signal, supplied by a Linear-Voltage Differential Transducer (LVDT) within the IGVA. This voltage signal has a linear relationship to the IGV position.
C. Surge Air
To prevent load compressor surge for all operating modes, altitudes, inlet temperatures, and aircraft airflow a surge control system is installed on the APU. The surge control system releases the load compressor air flow that the aircraft pneumatic system does not use. This keeps air moving through the load compressor and prevents compressor surge.
The main unit is the Surge Control Valve (SCV). The SCV is installed on the tee-duct in the aft direction to direct excessive bleed air overboard through the APU exhaust. The SCV is a hydraulic ally actuated butterfly valve, which is normally spring loaded open. A hydraulic ally operated actuator, controlled by an electrohydraulic servo valve, opens or closes the valve. The hydraulic power is supplied by the high pressure side of the FCU. The ECB controls the servo valve, via a torque motor, to open or close the butterfly valve of the SCV. An LVDT provides position feedback to the ECB.
The air pressure developed by the load compressor is sampled by the static pressure and total pressure probes. The Total Pressure transducer (PT) and the Delta Pressure (DP) transducer translate the pressure inputs into an electrical signal which are transmitted to the ECB.
Surge protection is controlled by the ECB. The ECB compares a corrected airflow and a surge margin set point.
The corrected airflow is the amount of air that flows through the load compressor. The ECB calculates the corrected airflow using the signals of the PT transducer and the DP transducer.
The surge margin set point is the minimum amount of air that should flow from the load compressor for APU operation condition. The surge margin set point is a function of the inlet temperature (T2), the inlet pressure (P2), the total pressure (PT), the delta pressure (dP) and the IGV position and the aircraft selected mode.
If the surge margin set point is more than the corrected air flow the ECB triggers the SCV to open. This keeps the airflow from the load compressor at the minimum level.
To prevent load compressor surge for all operating modes, altitudes, inlet temperatures, and aircraft airflow a surge control system is installed on the APU. The surge control system releases the load compressor air flow that the aircraft pneumatic system does not use. This keeps air moving through the load compressor and prevents compressor surge.
The main unit is the Surge Control Valve (SCV). The SCV is installed on the tee-duct in the aft direction to direct excessive bleed air overboard through the APU exhaust. The SCV is a hydraulic ally actuated butterfly valve, which is normally spring loaded open. A hydraulic ally operated actuator, controlled by an electrohydraulic servo valve, opens or closes the valve. The hydraulic power is supplied by the high pressure side of the FCU. The ECB controls the servo valve, via a torque motor, to open or close the butterfly valve of the SCV. An LVDT provides position feedback to the ECB.
The air pressure developed by the load compressor is sampled by the static pressure and total pressure probes. The Total Pressure transducer (PT) and the Delta Pressure (DP) transducer translate the pressure inputs into an electrical signal which are transmitted to the ECB.
Surge protection is controlled by the ECB. The ECB compares a corrected airflow and a surge margin set point.
The corrected airflow is the amount of air that flows through the load compressor. The ECB calculates the corrected airflow using the signals of the PT transducer and the DP transducer.
The surge margin set point is the minimum amount of air that should flow from the load compressor for APU operation condition. The surge margin set point is a function of the inlet temperature (T2), the inlet pressure (P2), the total pressure (PT), the delta pressure (dP) and the IGV position and the aircraft selected mode.
If the surge margin set point is more than the corrected air flow the ECB triggers the SCV to open. This keeps the airflow from the load compressor at the minimum level.
4. Interface
The bleed and surge air system has an interface with:
** ON A/C NOT FOR ALL The bleed and surge air system has an interface with:
- the APU Bleed Air Supply and Crossbleed System (Ref. AMM D/O 36-12-00-00),
- the APU Load Compressor (Ref. AMM D/O 49-23-00-00),
- the Control and Monitoring System (Ref. AMM D/O 49-61-00-00).
5. Component Description
A. Surge Control Valve (SCV)
The SCV is a hydraulically actuated butterfly valve with a position feedback from a linear variable differential transformer (LVDT) to the ECB. The SCV has also a visual position indicator.
Fuel pressure is routed to the spool valve and through the filter to the operating jet. With zero current applied to the torque motor, the torque motor is biased to supply high pressure and low pressure to the spool valve. The spool valve moves in relation to the pressure applied and allows pressure to open the valve. As current is applied to the torque motor, more pressure is applied to the spool valve. This results in the valve stroking towards the closed position.
Loss of the electrical signal (open circuit) will disable the SCV to the fully open position.
The SCV is a hydraulically actuated butterfly valve with a position feedback from a linear variable differential transformer (LVDT) to the ECB. The SCV has also a visual position indicator.
Fuel pressure is routed to the spool valve and through the filter to the operating jet. With zero current applied to the torque motor, the torque motor is biased to supply high pressure and low pressure to the spool valve. The spool valve moves in relation to the pressure applied and allows pressure to open the valve. As current is applied to the torque motor, more pressure is applied to the spool valve. This results in the valve stroking towards the closed position.
Loss of the electrical signal (open circuit) will disable the SCV to the fully open position.
B. Load Control Valve
The Load Control Valve (LCV) is a pneumatically actuated open butterfly valve. The valve flow section is made up of a valve body, a butterfly shaft and a butterfly plate. The valve body is a cylindrical air-flow duct, flanged at each end, for in-line installation with the air ducts. Flanges at the top and bottom of the valve body each have an axially-aligned bore for the butterfly shaft. The butterfly shaft is bearing mounted across the valve body and extends upward through the top of the actuator. The butterfly plate (attached to the butterfly shaft) operates as a spring-loaded air-flow flap inside the valve body.
The position-indicator switch assembly (installed on top of the pneumatic actuator) has:
The Load Control Valve (LCV) is a pneumatically actuated open butterfly valve. The valve flow section is made up of a valve body, a butterfly shaft and a butterfly plate. The valve body is a cylindrical air-flow duct, flanged at each end, for in-line installation with the air ducts. Flanges at the top and bottom of the valve body each have an axially-aligned bore for the butterfly shaft. The butterfly shaft is bearing mounted across the valve body and extends upward through the top of the actuator. The butterfly plate (attached to the butterfly shaft) operates as a spring-loaded air-flow flap inside the valve body.
The position-indicator switch assembly (installed on top of the pneumatic actuator) has:
- a switch lever,
- two switches,
- an electrical receptacle,
- a switch cover.
6. Operation/Control and Indicating
A. Start Procedure of APU Bleed-Air Supply
The start sequence of the APU is complete when the APU acquires 95% speed (Ref. AMM 49-42-00).
Above the acquired 95% + 2sec speed the APU is obtainable for the supply of bleed-air and electrical power.
Information on the ECAM and the overhead panel shows that the APU is available:
When you push the APU BLEED pushbutton switch:
The start sequence of the APU is complete when the APU acquires 95% speed (Ref. AMM 49-42-00).
Above the acquired 95% + 2sec speed the APU is obtainable for the supply of bleed-air and electrical power.
Information on the ECAM and the overhead panel shows that the APU is available:
- on the APU page of the lower ECAM display unit, the green AVAIL indication comes on,
- on the APU overhead panel 25VU, the green AVAIL legend on the APU START pushbutton switch comes on,
When you push the APU BLEED pushbutton switch:
- the blue ON legend in the APU BLEED pushbutton switch comes on,
- the BMC starts a test of the sensing elements on the APU bleed-air duct and the left wing bleed-air ducts. If the test is correct the BMC transmits a signal to the ECB. Then the ECB opens the APU load control valve.
NOTE: If the BMC 1 finds a leak in the APU bleed-air ducts, while there is a Main Engine Start (MES) signal from the engines, it ignores the leak signal and tells the ECB to open the APU bleed load valve.
B. Stop of the APU Bleed-Air Supply
To stop the APU bleed-air supply you release the APU BLEED pushbutton switch:
To stop the APU bleed-air supply you release the APU BLEED pushbutton switch:
- the blue ON legend on the APU BLEED pushbutton switch goes off,
- the BMCs remove the 'demand' signal to the ECB,
- the APU load control valve closes and stops the bleed air supply,
- on the BLEED and APU pages of the lower ECAM display unit, the APU bleed-valve symbol is shown in the closed position.
NOTE: If an APU emergency shutdown or an APU automatic shutdown occurs, the APU bleed air supply stops automatically.
NOTE: When the APU operates in the APU BLEED OFF condition:
- a random BLEED pressure figure is shown on the ECAM APU page.
- the indication on the ECAM BLEED page must not be more than 8 psi.
C. Indicating
The subsequent status of the bleed and surge air is shown on the lower ECAM display unit:
The subsequent status of the bleed and surge air is shown on the lower ECAM display unit:
- the load control valve position,
- the BLEED pressure indication in PSI.
(1) Load Control Valve Symbol
The ECB transmits the APU BLEED VALVE FC signal (label 037) from the load control valve to the SDACs for the position indication of the APU load control valve.
The ECB transmits the APU BLEED VALVE FC signal (label 037) from the load control valve to the SDACs for the position indication of the APU load control valve.
(2) BLEED Pressure Indication (PSI)
The ECB receives the air pressure signal from the total pressure transducer. It convertes the air pressure signal into digital data and transmits the BLEED AIR PRESSURE data (label 166) to the SDACs. The SDACs uses the CORRECTED AVERAGE STATIC PRESSURE data (label 246) from the ADIRS and BLEED AIR PRESSURE data to give the indication for the APU BLEED pressure in PSI.
The ECB receives the air pressure signal from the total pressure transducer. It convertes the air pressure signal into digital data and transmits the BLEED AIR PRESSURE data (label 166) to the SDACs. The SDACs uses the CORRECTED AVERAGE STATIC PRESSURE data (label 246) from the ADIRS and BLEED AIR PRESSURE data to give the indication for the APU BLEED pressure in PSI.