Pack Flow Control Valve

ATA21

2 Configuration of Air supply regulation with : Pack Flow selector and Econ Flow pushbutton.

  1. Econ flow pushbutton.
  • The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
  • The percentage of airflow from the flow control valves is selected by the ECON FLOW pushbutton switch 5HB.
  • The ECON FLOW pushbutton switch has two positions :
    • the ‘off’ position, which sets the flow control valve to 100% of the normal airflow,
    • the ON position, which sets the flow control valve to 80% of the normal airflow (The ON position can be selected for fuel economy purpose ).
  • The ECON FLOW pushbutton switch transmits the selected switch position to the ACSC 1 (Air Conditioning System Controller) and via ARINC interface to the ACSC 2. The ACSC calculates the necessary flow demand. Both ACSC set the flow control valves in the necessary reference position.
  • The flow control valves close automatically if:-there is an engine start,
    • there is an ENGINE FIRE pushbutton switch released,
    • there is a compressor overheat,
    • there is low bleed pressure,
    • the DITCHING pushbutton switch 13HL is in the on position,
    • the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

2. Pack Flow selector

  • The percentage of airflow from the flow control valves is selected by the FLOW selector pushbutton switch 5HB.
  • The FLOW selector pushbutton switch, which is located on the AIR COND panel 30VU, has three positions:
    • the NORM position, which sets the flow control valve to 100% of the normal airflow,
    • the LO position, which sets the flow control valve to 80% of the normal airflow.
    • the HI position, which sets the flow control valve to 120% of the normal airflow ( This position is selected in abnormal hot ambient conditions or to clear smoke ).

Pack Flow Control Valve

  • The flow control valve of the flow control unit is an electro-pneumatic butterfly valve with the main function :
    • Control of the mass flow of the bleed-air supply to the pack
    • Isolation of the pack from the bleed-air supply by crew selection, engine fire, ditching or engine start , ACM overheat and low pressure start up protection, controlled by the Air Conditioning System Controller (ACSC).
  • The ACSC1 controls the FCV for pack 1 and ACSC2 controls the FCV for pack 2. Each ACSC uses a close loop electronic control circuit to adjust the butterfly position and the necessary pack inlet flow.

Main component of FCV :

  • a torque-motor electrical adjustment
  • a duplex position sensor (Hall-sensor)
  • a Differential Pressure Sensor (DPS)
  • a Pack Inlet Pressure Sensor (PIPS)
  • a downstream pressure limiter
  • an on/off solenoid valve
  • a mode selection solenoid valve.
  • a three chamber pneumatic actuator
  1. Actuator

The FCV has a spring loaded actuator, which moves the butterfly valve. The supply pressure to operate the pneumatic actuator is tapped from the valve housing. It goes through the flange-assembly and a drilled passage to the inlet chamber of the pneumatic actuator.

2. Position Sensor

The duplex “Hall” uses two magnetic position sensors to indicate to the ACSC if the FCV is:

  • Fully closed (FC)
  • Not fully closed (NFC)

3. The FCV operates in the Main, electrical mode and the Back-up, pneumatic mode.

In the main mode, the flow of the FCV is determined through these conditions:

  • Different flow demands for correct cabin pressure,
  • Control priorities (take-off, landing, pack start),
  • Failures and pack overheat conditions.

In back-up mode, the downstream pressure limiter controls the flow of the FCV.

  • During pack start on ground, the on/off solenoid-valve is energized and the mode selection solenoid-valve is energized for 5 seconds. That means that the FCV operates in back-up mode for 5 seconds. During this time the ACSC monitors the valve function and position indication for failures. After 5 seconds, the FCV changes to main electrical control mode.
  • During pack start in flight, the on/off solenoid-valve is energized and the mode selection solenoid-valve is de-energized. The FCV operates immediately in main mode.

Main Mode Operation :

  • With the on/off solenoid-valve energized and the mode selection solenoid-valve de-energized, the actuator pressure and the flap position is related to the pressure leakage at the torque motor. The torque motor is driven directly by the ACSC . The air-flow through the venturi causes a pressure difference. The DPS measures the difference and sends the signal to the ACSC . The ACSC uses information from the two pressure sensors, along with aircraft cabin altitude and bleed air temperature to calculate the actual flow through the FCV . The ACSC compares the actual flow to the flow demand. If there is a difference, the ASCS drives the torque motor and adjusts the pressure in the actuator chamber. The pressure in the actuator chamber moves the shaft up and down against the spring force in the ambient chamber and the pressure in inlet chamber. The shaft moves and turns the lever together with the valve flap to get the required air-flow.

Back-up Mode Operation

  • With the mode-selection solenoid-valve energized, the actuator pressure and thus the valve flap position is related to the pressure leakage at the downstream pressure limiter . In back-up mode the supply pressure, which operates the pneumatic actuator, goes through the flange-assembly and a drilled passage to the inlet chamber of the pneumatic actuator . The pressure goes from the inlet chamber to the mode solenoid-valve and stops at the energized on/off solenoid . From the mode selection solenoid-valve goes the pressure to the pressure limiter . The downstream pressure goes through a drilled passage in the valve housing to the mode selection solenoid-valve and from there to the pressure limiter into the spring chamber. This pressure, together with the spring force, opens or closed the poppet valve and controls the pressure in the actuator chamber . The changed pressure in the actuator chamber moves the shaft up and down against the spring force in the ambient chamber and the pressure in the inlet chamber. The shaft moves and turns the lever together with the valve flap to get the required air-flow.

Overheat Protection

  • The ACSC monitors the compressor discharge temperature for overheat conditions. If the FCV operates in the main mode, a temperature of more than 215 DEG.C (419.00 DEG.F) at the compressor discharge sensor, will cause the ACSC to reduce the electrical supply of the torque motor. This reduces the vented air at the torque motor and therefore the pressure in the actuator chamber will decrease. This causes the spring in the ambient chamber to expand and moves the shaft. The shaft moves up and turns the lever together with the valve flap to decrease the air-flow to the pack . The reduced air-flow decreases the ACM speed and thus the compressor discharge temperature . A temperature of more than 260 DEG.C (500.00 DEG.F) at the compressor discharge sensor will cause a pack overheat warning. If the AC is on ground, the ACSC removes the electrical supply to the on/off solenoid valve. The FCV closes and stops the air-flow to the pack.

Operation Control

  • Normal Operation (packs running on engine bleed supply )
    • When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) then the flow control valves open . The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI position. This position selects the flow control reference in the ACSC 47HH (57HH) to 80%, 100% or 120%. When the PACK FLOW selector is set to the LO position, and the temperature demand cannot be reached, the ACSC will increase the normal airflow of the flow control valve from 80% to 100%.
  • APU in Operation (packs running on APU bleed air supply)
    • The ACSC 47HH (57HH) receives the APU bleed valve open signal . The flow control reference in the ACSC is set to 120% and the flow control valves are commanded to the fully open position.
  • Single Pack Operation (pack running on engine or APU bleed air supply)
    • Irrespective of which position the PACK FLOW selector is set to, the ACSC will modulate the pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.
  • Cả 3 chế độ hoạt động , PACK FLOW selector chỉ có ý nghĩa khi Pack hoạt động với Engine Bleed supply , còn 2 chế độ còn lại , ACSC luôn set up Flow là 120% , Pack flow control valve là fully open.
  • Operation with Failures
    • Single Pack Failure :
      • When the PACK FLOW selector is set to the NORM or LO position and there is a failure in one pack, the ACSC modulates the other pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.
    • Engine Fire :
      • If there is an engine fire, and you push the applicable FIRE pushbutton switch, the respective flow control valve closes. This stops the hot bleed air flow in order to prevent damage to the components of the air conditioning system and to prevent entry of smoke into the cabin
    • Ditching :
      • In case of landing on water the DITCHING pushbutton switch must be pushed. This closes the flow control valves which prevents the entry of water into the cabin through the air conditioning system.
    • Air-Cycle Machine Compressor Overheat :
      • If the compressor of an air-cycle machine exceeds 215 deg.C (419.00 deg.F), the ACSC and flow control valve will start to reduce the pack flow independent of the flow demand till the minimum flow demand is reached. When the compressor temperature reaches 260 deg.C (500.00 deg.F) (overheats) on ground, the ACSC will shut off the pack (flow control valve is closed).
    • Pack Shut-down in the Engine-Start Sequence
      • In the engine-start sequence (the EIU gives an engine rpm-signal of N2 below idle), normally both air-packs close. To prevent the complete pack shut-down in flight because of a wrong EIU-signal, the ACSC monitors the position of the Cross Bleed Valve (CBV) 6HV:
        • If the CBV is in the closed position, only one pack instead of both closes.

Note :

  • Electromagnet = Solenoid 1 On/Off
  • Electric Motor = Torque Motor And Quadrant
  • Solenoid = Solenoid 2 Mode selection
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