PACK OZONE CONTROL

OZONE FILTER 

An ozone filter is installed upstream of each Flow Control Valve (FCV). It is used for catalytic removal of ozone from the hot bleed air supplied to the pack.

DELTA P SENSOR AND FCV

A Differential Pressure (DELTA P) sensor connected to the FCV senses a differential pressure equivalent to the airflow through the valve inlet. This differential pressure is transformed into an electrical signal and sent to the Pack Controller (PC) for actual flow calculation.

 According to the actual flow calculation and the flow demand, the PC generates an FCV drive signal in order to control the FCV Torque Motor (TM). The valve butterfly is thus electro-pneumatically operated.

The FCV has a shut-off solenoid, which is energized in case of:

– engine start,

– opposite engine start, if the Crossbleed (X BLEED) valve is detected open, the FCV reopens 30 seconds after the end of the engine start sequence,

– ENG FIRE P/B released out,

– DITCHING P/B pressed in,

– applicable PACK P/B set to OFF.

The FCV also automatically closes in case of:

– low bleed pressure: valve spring-loaded closed,

– compressor overheat: muscle pressure venting by means of the compressor pneumatic overheat sensor.

BY-PASS VALVE

The BYPass valve regulates the pack discharge temperature by adding hot bleed air to the air cycle machine outlet for quick pack response. The BYP valve is electrically operated by a stepper motor controlled by the PC according to the water extractor temperature.

RAM AIR INLET FLAP

The ram air inlet flap modulates the airflow through the exchangers to control the temperature of the pack outlet. The PC controls an electric actuator that actuates the ram air inlet flap, according to the water extractor temperature in order to obtain optimum pack cooling airflow. The ram air inlet flap closes during take-off and landing to avoid ingestion of foreign material.

A.ICE VALVE

The Anti-ICE (A.ICE) valve removes any excessive ice formation across the condenser or maintains the pack outlet temperature at a fixed value, if the PC is unable to control the BYP valve. The A.ICE valve is pneumatically operated and electrically controlled by a solenoid:

– solenoid energized: the A.ICE valve pneumatically operates as an anti-ice function,

– solenoid de-energized: the A.ICE valve pneumatically operates as a temperature control valve. It maintains a pack outlet temperature of 15°C (59°F). An additional 3/2 way valve solenoid connected in parallel to the solenoid of A.ICE in order to resolve the back-up problem.

In normal mode:

– the solenoid is energized,

– the pipe assembly is open. In back-up mode:

– the solenoid is de-energized,

– the pipe assembly is closed.

The anti-ice function is done by two DELTA P relays for high and low pressure condenser flows. When the DELTA P increases due to restricted airflow caused by ice build-up, the related relays control the A.ICE valve to an open position. The pack outlet pneumatic sensor is used only to modulate the A.ICE valve to control the pack discharge temperature at a fixed value if there is PC failure.

AIR CYCLE MACHINE

The air cycle machine, which has a turbine, a compressor and a fan, cools the air. The main component of the air cycle machine is a rotating shaft. A turbine, a compressor and a fan are mounted along the shaft.

EXCHANGERS – REHEATER – CONDENSER

The air passes through two heat exchangers and a reheater before it enters the condenser, which causes the air temperature to drop well below dew point. The cooling agent for the primary heat exchanger and the main heat exchanger is outside ram air. The reheater is used to raise the temperature of the air before it reaches the turbine inlet to vaporize any remaining water droplets for turbine protection.

WATER EXTRACTOR

The water extractor collects water droplets and drains them inside the water extractor body in order to spray the collected water into the ram airflow of the exchangers, to increase the cooling efficiency.

CHECK VALVE

The pack downstream check valve stops leakage of air from the distribution system when the FCV is closed. The check valve is fitted to the pressure bulkhead.

Credit :    Rabindar Singh

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