-
indication and initialization purposes when in the automatic mode or,

 -
indication purposes when in the manual backup mode.

R **ON A/C 106-149, 151-199, 201-299, 301-399, 401-499,
 D. Protection Creel To prevent foreign objects entering the pressurized fuselage a metal grill is installed to brackets on the aircraft internal structure and completely covers the outflow valve.

 **ON A/C ALL
 E. Safety Valves (Ref. Fig. 016, 017) The safety valves 6HL (7HL) are poppet-type pneumatic valves. They have a valve part and a control part in a housing. The valve part has a cap with a filter, a diaphragm, a pedestal and a bellmouth. The control part has a position switch, a negative delta-P check-valve and a controller. The position switch is connected electrically to the System Data Aquisition Concentrators (SDACs). The negative delta-P check-valve opens if the external pressure is higher than the internal pressure. The controller has a diaphragm, a poppet and springs to preload the poppet. The poppet gives accurate limit control. If the internal pressure is more than the design goal of 8.6 psi (0.5929 bar) above the external pressure, the poppet moves and air flows out of the fuselage. For negative delta-P condition it is ensured by a minimum of one safety valve operating, that the internal pressure is not more than 0.07 bar (1.0152 psi) below the external pressure.
 7. Operation/Control and Indicating________________________________ 
R  **ON A/C 001-049, 051-099, 101-105, 151-199, 201-299, 301-302, 
R  (Ref. Fig. 001) 
R  **ON A/C 106-149, 303-399, 401-499, 
R  (Ref. Fig. 001A) 
R  **ON A/C ALL 
R  (Ref. Fig. 018)
 A. Automatic Operation No action of the crew is necessary. The CPCs receive landing elevation and QNH data from the FMGC and pressure altitude data from the ADIRUs. Only one CPC operates at a time, the other CPC is in standby. The active CPC sends demand signals to the electronic box of the outflow valve. The related auto-motor controls the outflow valve flap through a gearbox to the demanded position. The feedback module sends the position data through the electronic box to the CPC. On the PRESS page of the ECAM lower display unit the system status is shown.

 Safety Valve Figure 016
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 Cabin Pressure/Altitude Envelope Figure 017
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 Pressure Control System - Block Diagram Figure 018
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 70 seconds after each aircraft landing the active CPC changes to standby and the standby CPC changes to active.
 The CPCs pressurize the aircraft through 6 modes.
 (1)
 Ground Mode (GN) Before take-off and 55 seconds after landing, the active CPC controls the outflow valve to the fully open position to make sure that there is no residual delta-P in the aircraft. At touchdown, the CPCs controls the cabin V/S at -500 ft/mn. to release the remaining delta pressure.

 (2)
 Take-off Mode (TO) The active CPC pressurizes the aircraft with a rate of -400 ft/mn. until the delta pressure reaches 0.1 psi.

 (3)
 Climb Mode (CE) The active CPC controls the pressure in relation to the actual rate of climb of the aircraft.

 (4)
 Cruise Mode (CR)
 The cabin altitude is controlled to a constant delta-P.

 (5)
 Desent Mode (DE) The active CPC optimizes the pressure rate so that the cabin pressure reaches the landing field pressure just prior to landing. The maximum desent rate is limited to -750 ft/mn.

 (6)
 Abort Mode (AB) The active CPC uses the abort mode to prevent the cabin altitude from climbing if the aircraft does not climb after take-off. The cabin pressure is controlled to the value before the take-off.

 B. Semi-Automatic Operation If the FMGS data is not available, the CPCs use the barometric correction from the ADIRS and the landing elevation from the LDG ELEV selector switch in the cockpit to control the auto-motor of the outflow valve.
 C. Manual Operation The cabin pressure can be controlled manually from the CABIN PRESS overhead panel 25VU. When the MODE SEL pushbutton switch is pushed to the MAN position and the MAN V/S CTL switch is set to UP or DN, the manual motor and the gearbox moves the outflow valve flaps to the commanded position. The feedback module sends position signals to the backup part of the CPC 1 for indication.
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 The backup part gives the excess cabin altitude and the pressure data to the EIS. The data is shown on the PRESS page of the ECAM lower display unit. 
　
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