Flashcards in Pneumatic/ Air Conditioning/ Pressurization Deck (24)
Air Bleed System (Description)
-select the compressor stage from which air is bled, depending on the pressure and or temperature
-regulate air pressure between the HP Stage and the LP stage by the HP Valve
Bleed Air Users
Bleed Valve (Function)
Electro pneumatic bleed valve acts as a shut off valve when:
-Bleed Duct OVHT
-Bleed Duct LEAK
-Actuation of the associated ENG FIRE handle
-Engine failure at TO (UP TRIM signal)
-Prop Brake selected ON (for left bleed only)
-spring loaded closed in the absence of pressure
Cross-Feed Valve (Function)
A spring loaded, solenoid controlled valve connects the LH and RH air bleed systems
-On the ground, it is always open, except with both engines running and PropBrake disengaged
-In flight the cross-feed valve is normally closed
The valve is de-energized closed
Leak Detection System (Description)
Continuous monitoring system of 2 single loop assemblies (LH &RH) to detect leakage near the hot air ducts:
-Wing leading edge and wing to fuselage fairing
-Upper and lower fuselage floor
-Air conditioning pack area
Leak Detection System (Trigger)
Temperature above 153*C triggers LEAK light to illuminate and after 1s delay closes the associated Pack, HP and BLEED valves and GND X FEED if LH is affected
The crew must consider the associated bleed system as inop for the rest of the flight
Overheat Control System (Description)
Includes switches (duplicated for safety) installed near the the HP compressor exit and ensures the bleed valve and bleed air shut off valve close when temperature at or above 274*C is sensed
Associated Bleed system may be recovered after cooling
ENG BLEED OVHT Light
Illuminates amber and the CCAS is activated when either of the respective bleed duct OVHT sw operates at 274*C
System may be recovered
ENG BLEED LEAK Light
Illuminates amber and the CCAS is activated when either respective bleed leak detection system signals an alert when temperature rises above 153*C
System is considered inop
Air Conditioning (Description)
Air is processed through 2 packs installed in the main landing gear fairings. LH Pack for cockpit and cabin, RH for cabin only, though if either is inop, the other can supply both compartments.
Pack Valve (Function)
The pack valve is an electro-pneumatic valve, spring loaded closed, having 2 functions:
-Pack shut off
-Pressure control (NORM 22psi and HIGH FLOW 30psi)
Air flow through the AC Packs
Bleed air is admitted through the AC Packs, where it is cooled,dried, and compressed. It is cooled by air-to-air heat exchangers where external air is blown by:
-Ram air above 150kts
-2 ground turbofans at or below 150kts with the gear extended or with gear retracted for <10mins
Air Conditioning Ground Turbofans (Special Ops)
-In case of ENG OIL LOW PRESS, the turbo fan on the opposite side starts and runs as long as speed is 150kts or less, regardless of gear position.
-Incorrect position of a turbofan shut-off valve leads to closure of the associated pack valve.
Flight Deck Ventilation (Description)
The flight deck, FWD CARGO and electric and electronic equipment are ventilated by the flow of ambient air. The OVBD valve and the U/F valve work in conjunction to recirculate the air to the pressure vessel or duct it overboard.
OVBD Valve open = U/F Valve closed, and vice virsa.
OVBD Valve full open only if press diff is <1psi
Cabin Temperature Control
In AUTO MODE, the electronic temp controller computes temp control valve position using:
-Zone temp demand selector
-Associated compartment temp
-Aircraft skin temp
In MAN MODE, only the associated zone temp demand selector controls the temp control valve
Air Conditioning Overheat Protection
-When duct temp rises above 88*C, the limiter closes the temperature control valve progressively to reduce hot air flow.
-An OVHT caution is provided to the pilot when the duct temp rises above 92*C, leaving the pack valve open.
-The Pack Valve will auto close in case of overheat downstream of the pack compressor.
Flight Deck Ventilation Isolation
The EXTRACT AIR FLOW Valve allows the isolation of the flight deck in case of smoke in the FWD CARGO Compartment.
Pressurization System (Description)
Cabin pressure and rate of change is maintained by:
-An automatic digital controller
-A manual pneumatic controller
With 2 outflow valves, one electro-pneumatic and one pneumatic
In Auto mode the pneumatic is slaved to the other, in Manual mode, the electro-pneumatic is closed.
Pressurization System (Limitations)
Max Positive Diff Press 6.35psi
Max Negative Diff Press -0.50psi
Max Landing Diff Press 0.35psi
Max OVBD Valve full open 1.00psi
Max ALT for one BLEED off 20,000'
Pressurization Ops in AUTO MODE
The Digital Controller uses:
-Landing Elevation set in the landing elev. selector
-Takeoff Elevation stored in the controller
-Aircraft Static Pressure from ADC1 with CA Barro setting or ADC2 with STD Barro setting
This information is used to calculate a theoretical altitude which the controller uses to drive the outflow valves in order to match the actual altitude to the calculated theoretical altitude.
Pressurization Dump Mode
A DUMP function is available, in AUTO Mode only, to drive the electro-pneumatic valve full open. The DUMP switch is mechanically guarded.
Pressurization Manual Mode
The electro-pneumatic valve is maintained closed, leaving the pneumatic valve to maintain cabin pressure. The control knob is used to select any cabin rate of change from -1500fpm to +2500fpm
Pressurization Ditching Mode
2 electrical motors are used to drive the outflow valves to the closed position in either MAN or AUTO mode