The filtering and flow control system is found downstream of the bleed air system. Its functions are as follows:

• To pre-cool and control the temperature of the bleed air that comes from the pneumatic system and to supply it to the air conditioning system (also known as the pack).
  
  
• To measure and control the quantity of bleed air supplied to the pack and the temperature control system.
• To stop the supply of bleed air to the pack and the temperature control system when necessary.
• To give overheat protection to the pack and the temperature control system, and
• To decrease the quantity of ozone in the bleed air supplied to the pack and the temperature control system.

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There are two ozone converters (OZCs) installed in the aircraft, one in each line that supplies intermediate-pressure bleed-air. They are found in the aft equipment compartment, immediately downstream and adjacent to the flow control valves (FCVs).

Through catalytic process, the OZCs change the ozone molecules (O3) contained in the fresh air that comes from the intermediate-pressure bleed-air system into oxygen molecules (O2).

The OZCs contain a flow-through honeycomb monolith that has a layer of catalyst. It is the catalyst that causes the ozone to change to oxygen. The catalyst is not damaged or consumed in the reaction.

The OZCs are installed upstream of the pre-cooler so that high bleed air temperature can flow into them. High bleed air temperatures help the catalytic ozone conversion process.

The OZCs are life limited. At mid-life, the OZCs need to be restored to make sure that they will continue to operate satisfactorily. Refer to the Time Limits/Maintenance Checks for the scheduled maintenance of the OZCs.

Note:
Because the OZCs have a symmetrical shape,it is not possible to identify their forward and aft end in figure 2. To find the forward and aft end of the OZCs, refer to the nameplate attached to the body of the OZCs. An arrow symbol on the nameplate shows direction of airflow into the OZC.

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There are two differential pressure sensors installed in the aircraft, one in each line that supplies intermediate-pressure bleed-air. Differential pressure sensor No. 1 is found across the upper flow-sensor venturi-duct and differential pressure sensor No. 2 is found across the lower flow-sensor venturi-duct.

Note:
The upper flow-sensor venturi-duct and the lower flow-sensor venturi-duct are installed immediately upstream of the FCVs. They are components of the intermediate-pressure bleed-air system.

The differential pressure sensors are connected by sense lines to the flow-sensor venturi-ducts. They sense the difference in air pressure across the throat of the flow-sensor venturi-ducts. Their measurement range is 0 to 5 psi (0 to 34.47 kPa).

The data from the differential pressure sensors is used to measure mass flow for the environmental control system (ECS). Data from differential pressure sensor No. 1 goes to IAS controller No. 1, and data from differential pressure sensor No. 2 goes to IAS controller No. 2.

Routing of the sense lines is such that they can absorb duct movements and prevent water to collect (no low point).

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There are two FCVs installed in the aircraft, one in each line that supplies intermediate-pressure bleed-air. They are found in the aft equipment compartment, immediately upstream of the OZCs.

The FCVs control the supply of bleed air to the air conditioning system. They are two inch diameter, electrically controlled, pneumatic valves with a fail safe closed design (when there is no upstream air pressure, the FCVs are fully closed). Given that they have received a full open command, a full open position of the FCVs is guaranteed when bleed air pressure is more than 10 psi (68.95 kPa).

FCVs have the following parts:

• A 2 inch (5.08 cm) internal diameter valve body with a butterfly plate on an inclined axis. The butterfly plate is operated by a pneumatic actuator and is made out of high temperature stainless steel. The body of the valve has an upstream pressure line that supplies the regulator. The butterfly plate position is shown with an arrow shaped tab attached to the butterfly shaft. The words OPEN and CLOSED are written on the outside of the FCVs so that the position of the butterfly valve can be easily known.
  
  
• A pneumatic actuator made up of a cylinder, a diaphragm and a spring which closes the butterfly plate. The pneumatic actuator is made out of light alloy.

• A torque motor and a quadrant.
• An end of travel micro-switch operated by the butterfly shaft to indicate the butterfly valve's full closed or not full closed positions.

Note:
The FCVs are covered with a hard shell, thermal insulation jacket, to keep touch temperature to less than 392 °F (200 °C). The insulation jacket can be removed.

Internal operation of the FCVs is as follows:

• Through a pressure line, valve upstream pressure is supplied to the pneumatic actuator cylinder and to a chamber that contains the quadrant.
  
  
• The quadrant is operated by the torque motor and is installed in front of an orifice that lets air out of the pressure line. When the torque motor is energized, it causes the quadrant to move. When the quadrant moves, it causes the dimension of the orifice opening to change. The quantity of air pressure released from the pressure line is directly related to the dimension of the orifice opening.
  
  
• Because of the relation between the position of the quadrant, the dimension of the orifice opening and the quantity of air pressure released from the pressure line, it can be said that: A change in the position of the quadrant will cause an equivalent change in the quantity of air pressure in the pressure line.
  
  
• Because the quantity of air pressure in the pneumatic actuator cylinder is the same as the quantity of air pressure in the pressure line, it can also be said that: The quantity of current in the torque motor (which controls the quadrant position) controls the quantity of air pressure in the pneumatic actuator cylinder.
  
  
• The position of the butterfly plate is directly related to the quantity of air pressure in the pneumatic actuator cylinder. For instance, if the quantity of air pressure in the pneumatic actuator cylinder increases, the diaphragm pushes on the spring. This causes the spring to compress. The movement of the diaphragm is then transmitted to the butterfly valve through the butterfly shaft and its related linkage which causes the butterfly plate to open.

Torque motor current command is computed by the IAS controller. The quantity of current supplied to the torque motor is related to airflow demand by the air conditioning system and to the measured airflow feedback. A current of 250 mA (which is the maximum IAS controller torque motor current command output) is sufficient to operate a FCV to the full open position.

Note:
The left FCV is controlled by the IAS controller No. 1 and the right FCV is controlled by the controller No. 2.

When the torque motor is not energized, the pneumatic actuator cylinder is vented and the quantity of air pressure in the cylinder decreases. This causes the butterfly valve to go to its full closed position under the force of the actuator spring.

The maximum quantity of time necessary to open a FCV is less than 4 seconds. The maximum quantity of time necessary to close a FCV is less than 3 seconds.

Each FCV can be manually locked in the full closed position as follows:

• The butterfly plate must be moved to its full closed position through the hexagonal nut that is attached to the butterfly shaft. The position of the butterfly plate is shown with an arrow shaped tab attached to the butterfly shaft. When the butterfly plate is in the full closed position, a bore-hole drilled in the arrow shaped tab, aligns with a threaded boss on the valve body.
  
  
• The screw that is attached to one end of the pressure line must then be removed and screwed into the threaded boss on the valve body. For the screw to reach the threaded boss, it must go through the bore-hole in the arrow shaped tab.

The procedure given above makes sure that the pneumatic actuator cylinder is always vented to ambient air pressure. It also mechanically locks the butterfly shaft (and thus the FCV) in the closed position.

Note:
It is possible that an aircraft be approved for flight with only one FCV serviceable while the other one is unserviceable (mechanically closed and locked). Refer to the aircraft's minimum equipment list (MEL).

The FCVs fail safe closed design operates as follows:

• When there is no upstream bleed-air pressure, the spring found in the pneumatic actuator cylinder closes the valve. When there is a minimum of 10 psi (68.95 kPa) of upstream bleed-air pressure and the FCV torque motor is energized, the valve opens and controls the airflow. If the torque motor is not energized, the valve stays in the closed position.

 

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There is one pre-cooler inlet header installed in the aircraft and it is found in the aft equipment compartment. It connects the pack to the forward part of the pre-cooler.

The pre-cooler inlet header supplies the pre-cooler with exhaust ram air that comes from the pack. The pre-cooler inlet header is made of light alloy.

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There is one pre-cooler installed in the aircraft and it is found in the aft equipment compartment, downstream of the pack's ram air outlet and upstream of the ram air exhaust duct.

The pre-cooler decreases bleed air temperature to levels that are satisfactory for the operation of the air conditioning system. It also makes possible the use of light alloy material for the pack.

Hot bleed air that comes from the pneumatic system (engines or auxiliary power unit (APU) is cooled, by convection, with the exhaust ram air that comes from the pack. The pre-cooler is designed to limit the pack inlet and trim inlet air temperature to 430 °F (220 °C).

The pre-cooler is made of two air-to-air heat exchanger cores that are attached together. It has charged air inlets and charged air outlets for two isolated hot air paths (one for the supply of bleed air to the pack, and the other one for the supply of bleed air to the temperature control system). The charged air inlets and charged air outlets are standard 2 inch (5.08 cm) sheet metal connections.

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There is one pre-cooler outlet header installed in the aircraft and it is found in the aft equipment compartment. It connects the aft part of the pre-cooler to the ram-air outlet duct.

The pre-cooler outlet header collects the air that comes from the pre-cooler and sends it in the ram-air outlet duct. From the ram-air outlet duct, the air is then sent overboard through a louvered structural part.

The pre-cooler outlet header is made out of stainless steel. It has a thermal insulation jacket that keeps touch temperature to less than 392 °F (200 °C).

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Hot bleed air that comes from the pneumatic system (engines or APU) flows through the filtering and flow control system.

The filtering and flow control system has two isolated paths, one for each line that supplies bleed air. While bleed air enters the filtering and flow control system, it is measured by a differential pressure sensor which senses the difference in air pressure across the throat of a flow sensor venturi duct.

The position of the FCV is controlled by the IAS controller. The IAS controller uses the true mass airflow and the FCV airflow schedules to control the position of the FCV. The true mass airflow is calculated by the IAS controller with the data measured:

• By the differential pressure sensor. The data from the left differential pressure sensor No. 1 goes to IAS controller No. 1. The data from right differential pressure sensor No. 2 goes to IAS controller No. 2.
  
  
• By the bleed pressure transducer. The data from the left bleed transducer No. 1 goes to IAS controller No. 1. The data from right bleed pressure transducer No. 2 goes to IAS controller No. 2.
  
  
• With the bleed air temperature (estimate).

Note:
The bleed air temperature estimate is calculated from the data that follows: N2, total air temperature and aircraft altitude.

The FCV airflow schedules are calculated to supply the pack with a sufficient quantity of air with a relation to the engine bleed configuration (to optimize cabin comfort and keep the bleed air penalty to a minimum).

Bleed air then goes through an OZC to decrease the quantity of ozone concentration in it (ozone molecules are changed into oxygen molecules).

When the bleed air comes out of the OZC, it goes through the pre-cooler. The pre-cooler uses ram air that comes from the pack (exhaust ram air) to decrease the temperature of the bleed air supplied to the pack and the temperature control system.

While ram air flows around the cold side of the fins attached to the pre-cooler heat exchanger cores, heat is removed by convection. This heat comes from the bleed air that flows into the channels of the heat exchanger cores (where the hot side of the fins collect the heat). Heat transfer between the hot and the cold side of the fins is done by metal conduction.

The pre-cooler inlet and outlet headers are mechanical interfaces to the pre-cooler. The pre-cooler inlet header takes the exhaust ram air that comes from the pack and sends it to the pre-cooler. The pre-cooler outlet header collects the air that comes from the pre-cooler and sends it in the ram air exhaust duct. This air is then sent overboard.

Displays

The L (R) BLEED FAIL caution message will show when the FVC has failed in the not full closed position. The L (R) BLEED FAULT advisory message when:

• The left (right) bleed pressure sensor supplies no signal to the No. 1 (No. 2) IAS controller
• The left (right) bleed pressure sensor supplies an out of range signal to the No. 1 (No. 2) IAS controller
• The left (right) FCV is indicating always full closed
• The left (right) FCV is indicating always not full closed
• The left (right) No. 1 (No. 2) IAS controller has a malfunction

The EICAS messages that follow are related to the filtering and flow control system:

EICAS MESSAGE(S)	LEVEL (COLOR)
L BLEED FAIL	CAUTION (amber)
R BLEED FAIL	CAUTION (amber)
L BLEED FAULT	ADVISORY (cyan)
R BLEED FAULT	ADVISORY (cyan)

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The status of the FCVs (valve opened/valve closed) is shown on the ECS synoptic page. The FCVs are shown with a fixed contour and a flow line that moves. The contour color is white and the flow line color is usually the same as one of the adjacent flow lines. The flow line color can be one of those that follow:

• Red—Unserviceable status
• Amber—Caution
• White—Usual status with no airflow
• Green—Usual status with airflow
• Magenta—Invalid or unknown status

Continuous built-in tests (BITs) are done on the following components:

• Differential pressure sensors
• FCVs

For the differential pressure sensors, a fault condition is sensed when the sensor electrical acquisition is out of range (0.5 to 9.5 VDC). Confirmation time is 5 seconds. When a differential pressure sensor fault condition is sensed, a L or R BLEED FAULT advisory message is shown on the EICAS.

The following two possible FCV fault conditions are monitored:

• FCV unserviceable in the closed position
• FCV unserviceable in the not full closed position

A fault condition in the closed position is sensed when the FCV stays in the closed position after it has received a FCV open command. Confirmation time for the fault condition is 5 seconds.

When a FCV unserviceable in the closed position fault condition is sensed, a L or R BLEED FAULT advisory message is shown on the EICAS.

Note:
This fault condition is not sensed while the FCV operates or when bleed-air pressure is less than 15 psi (103.42 kPa).

A fault condition in the not fully closed position is sensed when the FCV stays in the open position after it has received a FCV close command. Confirmation time for the fault condition is 5 seconds.

When a FCV unserviceable in the not full closed position fault condition is sensed, a L or R BLEED FAIL caution message is shown on the EICAS.

The IAS controllers also monitor feedback from the current command to the FCV torque motor and compare that feedback to the air source selection input from the AIR COND / BLEED control panel. If a fault condition is sensed, a L or R BLEED FAIL caution message is shown on the EICAS.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
-	OZONE CONVERTER	ZONE(S) 311/312	21-51-01
MT23	DIFFERENTIAL PRESSURE SENSOR (FWD)	ZONE(S) 311/312	21-51-03
MT24	DIFFERENTIAL PRESSURE SENSOR (AFT)	ZONE(S) 311/312	21-51-03
MPE4	FLOW CONTROL VALVE (FWD)	ZONE(S) 311/312	21-51-09
MPE3	FLOW CONTROL VALVE (AFT)	ZONE(S) 311/312	21-51-09
-	PRE-COOLER INLET HEADER	ZONE(S) 311/312	21-51-11
-	PRE-COOLER	ZONE(S) 311/312	21-51-15
-	PRE-COOLER OUTLET HEADER	ZONE(S) 311/312	21-51-17

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