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R Each air conditioning pack has a flow control valve which gives
R variable flow and shut off control. These valves are
R electro-pneumatically operated.
R They will open when the PACK 1 (2) pushbutton switches are pushed in
R (the OFF legends go off) if the conditions which follow exist:
R - the engines are not in a starting sequence,
R - an ENGINE FIRE pushbutton switch is in the normal position (the
R light in the pushbutton switch is off),
R - the DITCHING pushbutton switch 13HL is released (the ON legend is
R off),
R - the bleed air pressure is more than the minimum pressure needed to
R open the flow control valves.
R (2) Normal Operation (packs running on engine bleed supply)
R When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the
R OFF legends go off) the flow control valves open.
R The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI
R position.
R - This position selects the flow control reference in the ACSC 47HH
R (57HH) to 80%, 100% or 120%.
R - The ACSC calculates the necessary flow and then sets the flow
R control valves 23HB (24HB) to the demanded position.
R When the PACK FLOW selector is set to the LO position, and the
R temperature demand cannot be reached, the ACSC will increase the
R normal airflow of the flow control valve from 80% to 100%.
R (3) APU in Operation (packs running on APU bleed air supply)
R When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the
R OFF legends go off) the flow control valves open.
R The ACSC 47HH (57HH) receives the APU bleed valve open signal.
R The flow control reference in the ACSC is set to 120% and the flow
R control valves are commanded to the fully open position.
R (4) Single Pack Operation (pack running on engine or APU bleed air
R supply)
R When a pack pushbutton switch is pushed in (the OFF legend goes off)
R the respective flow control valve opens.
R Irrespective of which position the PACK FLOW selector is set to, the
R ACSC will modulate the pack to the 120% (HI) mode. Thus the flow
R control valve is commanded to the fully open position.
R 1EFF : 401-499, 1 21-51-00Page 56 1 1 Aug 01/05 1 1 1CES 1
R (5) Operation with Failures
R (a) Single Pack Failure
R When the PACK FLOW selector is set to the NORM or LO position and
R there is a failure in one pack, the ACSC modulates the other pack
R to the 120% (HI) mode. Thus the flow control valve is commanded
R to the fully open position.
R (b) Engine Fire
R If there is an engine fire, and you push the applicable FIRE
R pushbutton switch, the respective flow control valve closes. This
R stops the hot bleed air flow in order to prevent damage to the
R components of the air conditioning system and to prevent entry of
R smoke into the cabin.
R (c) Ditching
R In case of landing on water the DITCHING pushbutton switch must
R be pushed. This closes the flow control valves which prevents the
R entry of water into the cabin through the air conditioning
R system.
R (d) Air-Cycle Machine Compressor Overheat
R If the compressor of an air-cycle machine exceeds 215 deg.C
R (419.00 deg.F), the ACSC and flow control valve will start to
R reduce the pack flow independent of the flow demand till the
R minimum flow demand is reached.
R When the compressor temperature reaches 260 deg.C (500.00 deg.F)
R (overheats) on ground, the ACSC will shut off the pack (flow
R control valve is closed).
R (e) Pack Shut-down in the Engine-Start Sequence
R In the engine-start sequence (the EIU gives an engine rpm-signal
R of N1<50%), normally both air-packs close.
R To prevent the complete pack shut-down in flight because of a
R wrong EIU-signal, the crossbleed valve indication relay 7HV
R monitors the position of the Cross Bleed Valve (CBV) 6HV:
R - If the CBV is in the closed position, only one pack instead of
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