The intermediate pressure bleed air system uses bleed air from the engines to supply the dependent systems. Air to the system is supplied either by both engines, by the auxiliary power unit, or a high-pressure ground connection.

The intermediate pressure bleed air system is divided into left and right sides, both isolated by a crossbleed valve. System pressure is controlled by regulating and shutoff valves (SOVs). The system supplies pressurized air to the air-conditioning system and to the engine starters.

The intermediate-pressure bleed-air system has a system of bleed ducts. The bleed ducts are made of stainless steel alloy. The ducts are installed under tension, so that they can absorb the growth during thermal expansion. One exception is the cross-over line, which is installed under compression and thermal expansion and structural deflections are absorbed by the ducting flexion. Ducts are installed with multiple sliding supports and with a minimum of hard mounts. Hard mounting is done by tie rods or direct attachment to structural brackets. Ball joints and gimbals are installed along the ducting to cope with manufacturing and installation tolerances, structural movement, and thermal expansion of the pipes.

The bleed ducts have insulation to prevent the duct surface temperature to be more than 200 °C (392 °F). The insulation shell is drilled with small holes. Air leakage from the ducts is collected in the shell and released through the holes. The holes point the air leakage on the leak detection loops. The bleed ducts have flanges and are attached to each other with V-band couplings. Silicone rubber covers are installed on the V-band couplings.

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There are two intermediate pressure valves (IPVs), installed in the left and right side of the aft equipment compartment, near the pylon interface. The IPV is a 2-inch diameter, electrically controlled, pneumatic valve. The left IPV gets power from the L ESS BUS (CB1-D15). The right IPV gets power from the R ESS BUS (CB2-D15). It regulates the bleed air from the intermediate-pressure engine port. The IPV controls the air flow to a nominal 50 ± 3 psig (344.74 ± 20.68 kPa). The IPV is spring-loaded to the closed position.

The IPV is made of the parts that follow:

• A butterfly valve, which has a 2-inch diameter valve body and butterfly plate on an inclined axis. The valve body and butterfly plate are made of high temperature stainless steel. The valve body has an upstream pressure tapping to supply the pressure regulator with pressurized air. Butterfly position is indicated with an arrow attached to the butterfly shaft. The words OPEN and CLOSED are written on the valve body.
  
  
• A pressure reducer and a pressure regulator, which control the pressure in the valve actuation chamber of the pneumatic actuator. They each have a diaphragm, a clapper, and a spring.
  
  
• A pneumatic actuator, which has a diaphragm, a cylinder assembly and a spring which closes the butterfly plate. The actuator is made of light alloy.
  
  
• A solenoid valve, installed downstream of the pressure reducer.
  
  
• A microswitch, which is operated by the butterfly valve. The microswitch indicates the valve position: FULL CLOSED or NOT FULL CLOSED.

With no upstream pressure, the IPV is closed. When upstream pressure reaches 10 psig (68.95 kPa) and current is applied to the solenoid valve, the IPV opens. When current is removed, the IPV closes.

The pressure regulation is entirely pneumatic. Upstream air pressure is supplied to the pressure reducer which then pressurizes the pressure regulator. The pressure regulator controls the pneumatic actuator. Downstream air pressure is measured by a pressure connection downstream of the IPV and connected to the pressure regulator. The downstream pressure measurement is used to control the pressure regulator, which controls the pressure in the pneumatic actuator. When the pressure goes above 50 psig (344.74 kPa), the pneumatic actuator moves the butterfly plate towards the closed position. When the pressure falls under 50 psig (344.74 kPa), the butterfly plate moves back to the full open position.

 

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There are two bleed check valves, installed on the left and the right side of the aft equipment compartment, downstream of the IPVs. They are used to prevent reverse air flow into the engines. The bleed check valve is 2-inch diameter, double flapper, insert-type check valve. The valve is inserted and clocked into the downstream flange of the IPV. The bleed check valve is spring-loaded to the closed position.

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There are two bleed pressure transducers installed on the left side of the aft equipment compartment, downstream of the IPVs. The transducer related to the right side of the bleed air system is located forward of the left intermediate port discharge duct. The transducer related to the left side of the bleed air system is located aft of the left intermediate port discharge duct. The transducer is an absolute pressure sensor that measures pressure from 0 to 75 psig (0 to 517.11 kPa) and sends this data to the IAS controller. It is used to monitor IPV pressure regulation to be shown on the ECS synoptic page. The bleed pressure transducer related to the left side of the bleed air system gets power from the L ESS BUS (CB1-D14). The bleed pressure transducer related to the right side of the bleed air system gets power from the R ESS BUS (CB2-D14).

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There is one crossbleed valve (CBV), installed in the aft equipment compartment. The CBV connects the left and right intermediate pressure bleed air systems, downstream of the IPVs and bleed check valves. The CBV connects the lower flow sensor venturi duct to the intermediate crossover duct. The CBV is opened automatically by the IAS controller during engine startup. The IAS controller closes the CBV when the engines are operational. The CBV can also be manually controlled through the AIR COND/BLEED control panel. The CBV is an electrically operated actuator valve. It gets power from the R ESS BUS (CB2-D12). FULL OPEN and FULL CLOSED valve positions are monitored by end-of-travel microswitches. The valve body is made of stainless steel. The CBV also has a manual lever to secure the valve closed for dispatch. The CBV flanges are machined interfaces. The upstream flange has a notch to make sure it is correctly installed.

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There is one high-pressure ground connection (HPGC) attached to the aircraft skin near the aft equipment compartment. It is used to connect the bleed air system to an external high-pressure ground air-supply source. Access to the HPGC is through the ground-air servicing-connection door. The door is found in the rear fuselage to the right of the lower center-line. The HPGC has a machined stainless steel body and a double-flapper check valve. The HPGC is spring-loaded to the closed position.

The HPGC body has a standard interface for connection to a high-pressure ground air-supply source and an annular flange with boreholes which connects to the flange of the high-pressure ground duct.

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High-Pressure Ground Duct

There is one high-pressure ground duct, installed on the right-side of the aft equipment compartment. It connects the HPGC to the auxiliary power unit (APU) line duct.

The high-pressure ground duct has an annular flange with boreholes which connects to the flange of the HPGC.

Intermediate Port Discharge Ducts

There is one left intermediate port discharge duct installed at the interface between the left pylon and the aft equipment compartment. It connects the left engine bleed air supply to the left IPV.

There is one right intermediate port discharge duct, installed at the interface between the right pylon and aft equipment compartment. It connects the right engine bleed air supply to the right IPV.

APU Discharge Duct

There is one APU discharge duct, installed in the aft equipment compartment. It connects the APU bleed air duct to the APU line duct.

Note:
The APU bleed air duct is a component of the APU bleed air ducting.

APU Line Duct

There is one APU line duct, installed in the aft equipment compartment. It connects the APU discharge duct, the high pressure ground duct and the output of the right IPV to the intermediate cross-over duct and to the right air-turbine starter-duct.

Air Turbine Starter Ducts

There is one left air turbine starter duct installed at the interface between the left pylon and the aft equipment compartment. It connects the left air turbine starter (ATS) valve to the lower flow sensor venturi duct, on the forward left side.

There is one right air turbine starter duct, installed at the interface between the right pylon and the aft equipment compartment. It connects the right ATS valve to the APU line duct, forward of the intermediate cross-over duct.

Intermediate Crossover Duct

There is one intermediate crossover duct installed in the aft equipment compartment. It connects the APU line duct on the right side to the upper flow sensor venturi duct and to the CBV on the left side.

Lower Bleed Duct

There is one lower bleed duct installed in the left aft equipment compartment. It connects the ozone converter to the lower precooler inlet duct.

Note:
The ozone converter is a component of the filtering and flow control system.

Upper Bleed Duct

There is one upper bleed duct installed in the aft equipment compartment, left side. It connects the ozone converter to the upper precooler inlet duct.

Precooler Inlet Ducts

There is one lower precooler inlet duct installed in the aft equipment compartment. It connects the lower bleed duct to the precooler.

Note:
The pre-cooler is a component of the filtering and flow control system.

There is one upper precooler inlet duct installed in the aft equipment compartment. It connects the upper bleed duct to the precooler.

Pack Inlet and Outlet Ducts

There is one pack inlet duct installed in the aft equipment compartment. It connects the precooler to the precooler crossover valve and the filtering and flow control system. This duct also has a connection for the pack inlet temperature sensor (PITS).

Note:
The pre-cooler cross-over valve and the PITS are components of temperature control and indication.

There is one pack outlet duct, installed in the aft equipment compartment. It connects the precooler and the precooler crossover valve to the trim air duct. The pack outlet duct also has a connection for the hot air temperature sensor (HATS).

Note:
The HATS and the trim air duct are components of temperature control and indication.

Engine Nacelle Low-Pressure Bleed Duct

There are two engine nacelle low-pressure bleed ducts. One is in the left engine nacelle and the other is in the right engine nacelle. They connect the low-pressure port of the engines to their related intermediate port discharge duct.

Lower Flow Sensor Venturi Duct

There is one lower flow sensor venturi duct, installed on the left side of the aft equipment compartment. It connects the CBV, the left IPV, and the left ATS duct to the lower flow control valve (FCV). This duct also has a connection for a differential pressure sensor.

The pressure sensor measures the air flow across the lower flow sensor venturi duct for the air conditioning system.

Note:
The FCV and the differential pressure sensor are components of the filtering and flow control system.

Upper Flow Sensor Venturi Duct

There is one upper flow sensor venturi duct, installed in the aft equipment compartment. It connects the CBV to the upper FCV. This duct also has a connection for a differential pressure sensor. This pressure sensor measures the air pressure across the upper flow sensor venturi duct for the trim air supply.

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The AIR COND/BLEED control panel is installed in the flight compartment center pedestal. It controls the left and right intermediate-pressure bleed air and APU bleed air selection. It also controls the air-conditioning system, ram air system, and temperature control and indication system.

The COCKPIT and CABIN temperature selectors control the temperature in the flight compartment and passenger compartment. They send signals to the IAS controllers to control the air temperature of each zone in the range of 59 to 95 °F (15 to 35 °C).

The RAM AIR PBA controls the ram air valve. When this PBA is pushed, the light comes on, an EICAS message is shown, and the ram air valve opens. The PBA has a guard to prevent accidental selection of the ram air.

The L BLEED and R BLEED PBAs on the AIR COND/BLEED control panel control the right and left engine bleed air source. These PBAs are used to control the related engine bleed air supply. When the L (R) BLEED PBA is pushed, the light comes on, displaying OFF, and the left/right IP closes.

The X BLEED PBA controls the crossbleed valve (CBV). When X BLEED PBA is pushed, the light comes on, an EICAS message is shown and the CBV opens. Selection of this PBA a second time closes the CBV. The crossbleed valve opens automatically during engine start and the X BLEED PBA lights according to the valve position.

The APU PBA controls the supply of bleed air from the APU. When this PBA is pushed, the light comes on and the APU load control valve opens. Selection of this PBA a second time closes the valve.

When all bleed sources are off, a BLEED OFF status message is displayed on the EICAS.

The AIR SOURCE rotary switch has the functions that follow:

• OFF—Air-conditioning system (pack) and the temperature control and indication system (trim air) do not operate; selection of OFF closes both FCVs. When selected, an AIR SOURCE OFF status message is shown on the EICAS.

• NORM—Set by the flight crew in usual operation. Pack and the trim air are active. For automatic and manual mode, the pack supplies cool dry air to the flight and passenger compartments (zones) and controls the temperature of the gaspers air supply. In automatic mode, the trim air supplies hot air to each zone. Because the trim air operates in this configuration, there is an independent control of the air supply to the zones and gaspers.

  • When NORM is selected, automatic mode is initiated. In this mode, the COCKPIT and CABIN temperature selectors and the ventilated temperature sensors (VENTSs) are the inputs to the IAS controllers to control the air temperature.
    
    
  • When NORM is selected and the MAN TEMP PBA is pushed, the manual mode is set. In this mode, the COCKPIT and CABIN temperature selectors and the duct temperature sensors (DTSs) are the inputs to the IAS controllers to control the temperature.

Note:
The VENTSs and DTSs are components of temperature control and indication.

• PACK ONLY—Set by the flight crew if the trim air becomes unserviceable. Selection closes the right FCV, the precooler cross valve and both hot air regulating and shutoff valves (HARSOVs). Also, a PACK ONLY status message is shown on the EICAS.
  
  Note:
  The HARSOVs are components of temperature control and indication.

  • For automatic and manual mode, the pack supplies air to each zone and controls air temperature; the trim air does not operate. As such, there is no independent control of the air supply to the zones and the gaspers.
    
    
  • When PACK ONLY is selected on the AIR SOURCE switch, the automatic mode is set. When PACK ONLY is selected and the MAN TEMP PBA is pushed, manual mode is set. When selected, a PACK ONLY status message is shown on the EICAS.

• TRIM AIR ONLY—Set by the flight crew if the pack becomes unserviceable. Selection closes the left FCV, the precooler cross valve and opens the HARSOVs. Also, a TRIM AIR ONLY status message is shown on the EICAS.
  

  • When TRIM AIR ONLY is selected, the trim air supplies hot air to each zone; the pack does not operate. As such, there is no independent control of the air supply to the zones and the gaspers.
    
    
  • When TRIM AIR ONLY is selected with the AIR SOURCE switch, the automatic mode is set. When TRIM AIR ONLY is selected and the MAN TEMP PBA is pushed, manual mode is set. When selected, a TRIM AIR ONLY status message is shown on the EICAS.

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The intermediate-pressure bleed-air system gets its air supply from three different sources: the engines, the APU, or from an external high-pressure ground air-supply source, via the HPGC. All three sources can be used to start the main engines and supply the air-conditioning system with pressurized air. Air source selection and valve control is done manually through the AIR COND/BLEED control panel. During engine start, the IAS controller opens the CBV. The IAS controller closes the CBV when the engines are operational.

The main engines can start only when pressurized air is supplied to the ATSs. Air is supplied either from the APU, the HPGC, or from the opposite engine, if in operation. During usual engine start, the flow control valves and the IPVs are closed and the CBV is open.

On ground, with both engines shut down, either the APU or the HPGC supplies the intermediate-pressure bleed-air system with pressurized air. The IPVs are closed and the bleed check valves prevent reverse airflow into the engines. The CBV is open to supply both the pack and the trim air.

In flight, the APU or an engine already in operation supplies pressurized air. The IPVs are closed and the bleed check valves prevent reverse airflow into the engines. The CBV is open to supply both the pack and the trim air.

Also in flight, the air-conditioning system is usually supplied with pressurized air from the engine bleed air supply. In this case, the IPVs are opened, and control the pressure of the bleed air. The bleed check valves are also open. The CBV is closed to isolate the left and right-hand sides. This prevents damage and excessive wear from a difference in pressure between the left and right engine.

When the bleed pressure transducer senses pressure in the system less than 15 psi (103.42 kPa), it sends a signal to the IAS controller. The controller then sends a signal to the data control unit (DCU), which shows a L (R) BLEED FAIL caution message on the EICAS. If there is a malfunction of the bleed pressure transducer, an L (R) BLEED FAULT advisory message is shown on the EICAS.

If the CBV does not open or close when commanded, a signal is sent to the DCU, through the IAS controller. At this time, a X BLEED FAIL caution message is shown on the EICAS. If a valve becomes defective, or a duct ruptures, an L (R) BLEED FAIL caution message is shown on the EICAS. In this event, the IAS controller isolates the defective side of the intermediate-pressure bleed-air system to increase reliability.

When the MAN TEMP PBA on the AIR COND/BLEED control panel is pushed, the light turns on and the air conditioning pack operates in the manual mode. This will cause the legend MANUAL (in white) to show on the ECS synoptic page between the COCKPIT and CABIN temperature indications. Also, an AIR COND MAN TEMP ON status message is shown on the EICAS.

When OFF is selected on the AIR COND/BLEED control panel an AIR SOURCE OFF status message is shown on the EICAS. When the L, R and APU bleeds are off, a BLEED OFF status message is shown on the EICAS. When PACK ONLY is selected on the AIR COND/BLEED control panel, a PACK ONLY status message is shown on the EICAS. When TRIM AIR ONLY is selected on the AIR COND/BLEED control panel, a TRIM AIR ONLY status message is shown on the EICAS. When X BLEED PBA is pushed, a XBLEED OPEN status message is shown on the EICAS. When RAM AIR PBA is pushed, a RAM AIR ON status message is shown on the EICAS.

The EICAS messages that follow are related to the intermediate-pressure bleed-air system:

EICAS MESSAGE(S)	LEVEL (COLOR)
L BLEED FAIL	CAUTION (amber)
R BLEED FAIL	CAUTION (amber)
X BLEED FAIL	CAUTION (amber)
L BLEED FAULT	ADVISORY (cyan)
R BLEED FAULT	ADVISORY (cyan)
AIR COND MAN TEMP ON	STATUS (white)
AIR SOURCE OFF	STATUS (white)
BLEED OFF	STATUS (white)
PACK ONLY	STATUS (white)
RAM AIR ON	STATUS (white)
TRIM AIR ONLY	STATUS (white)
XBLEED OPEN	STATUS (white)

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The intermediate-pressure bleed air system has interfaces with the systems or components that follow:

• Integrated air system (IAS) controller
• Differential pressure sensor
• Flow control valve
• Ozone converter
• Precooler
• Dual heat exchanger
• Temperature control and indication
• Bleed-air leak detection system
• Airborne auxiliary power
• Starting

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Two IAS controllers monitor the intermediate-pressure bleed-air system. The IAS controllers use the bleed pressure transducers to monitor system pressure. The controllers also use the microswitches on the IPVs to monitor valve position. The IAS controllers then shows this information on the EICAS, on the air-conditioning synoptic page.

The status of the IPVs (valve opened/valve closed) is shown on the ECS synoptic page. The IPVs 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 the one of the adjacent flow lines. The flow line color can be one of those that follow:

• Red to show an unserviceable status
• Amber to show a caution
• White to show a usual status with no airflow
• Green to show a usual status with airflow
• Magenta to show invalid or unknown status

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
MT21	BLEED PRESSURE TRANSDUCER (LH)	ZONE(S) 312	36-11-03
MT22	BLEED PRESSURE TRANSDUCER (RH)	ZONE(S) 312	36-11-03
V3	INTERMEDIATE PRESSURE VALVE (LH)	ZONE(S) 311	36-11-05
V4	INTERMEDIATE PRESSURE VALVE (RH)	ZONE(S) 312	36-11-05
-	BLEED CHECK VALVE	ZONE(S) 311 ZONE(S) 312	36-11-09
MPE2	CROSS-BLEED VALVE	ZONE(S) 311	36-11-15
-	HIGH-PRESSURE GROUND CONNECTION	ZONE(S) 330	36-11-17

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