-
the BLEED pressure indication in PSI.
APU Bleed Load Valve - Interface to ECB and BMC,s
Figure 003
CES
(1)
Load Control Valve Symbole 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.
BLEED AND SURGE AIR - DESCRIPTION AND OPERATION
_______________________________________________
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.
2.
Component Location
__________________
(Ref. Fig. 001, 002, 003)
-------------------------------------------------------------------------------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 PRESSUE 316 316AR 49-51-20 VALVE - LOAD CONTROL 316 316AR 49-51-51 VALVE - SURGE CONTROL 316 316AR 49-51-52
3. System Description
__________________
(Ref. Fig. 004)
A. 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.
R EFF : 001-049, 101-105, 107-107, 151-199, 49-51-00Page 1 201-210, Config-2 Aug 01/05
CES
Bleed and Surge Air - Component Location
Figure 001
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Bleed and Surge Air - Component Location
Figure 002
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Bleed and Surge Air - Component Location
Figure 003
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Bleed and Surge Air - Block Diagram
Figure 004
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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:
-MES
-ECS, To control the bleed air flow, delivered by the load compressor, and to prevent APU overtemperature it is necessary to regulate the air flow guided to the load compressor inlet. This is achieved by the Inlet Guide Vanes (IGV). 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
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