B737NG/36/301 Pneumatic System
Boeing 737-600/700/800/900
Pneumatic System Training manual For training purposes only LEVEL 3
ATA 36
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B737NG/36/301 Pneumatic System
Training manual
This publication was created by Sabena technics training department, Brussels-Belgium, following ATA 104 specifications. The information in this publication is furnished for informational and training use only, and is subject to change without notice. Sabena technics training assumes no responsibility for any errors or inaccuracies that may appear in this publication. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of Sabena technics training.
Contact address for course registrations course schedule information Sabena technics training
[email protected]
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B737NG/36/301 Pneumatic System
List of Effective Pages 1.......................... 10 - 12 - 2013 2.......................... 10 - 12 - 2013 3.......................... 10 - 12 - 2013 4.......................... 10 - 12 - 2013 5.......................... 10 - 12 - 2013 6.......................... 10 - 12 - 2013 7.......................... 10 - 12 - 2013 8.......................... 10 - 12 - 2013 9.......................... 10 - 12 - 2013 10........................ 10 - 12 - 2013 11......................... 10 - 12 - 2013 12........................ 10 - 12 - 2013 13........................ 10 - 12 - 2013 14........................ 10 - 12 - 2013 15........................ 10 - 12 - 2013 16........................ 10 - 12 - 2013 17........................ 10 - 12 - 2013 18........................ 10 - 12 - 2013 19........................ 10 - 12 - 2013 20........................ 10 - 12 - 2013 21........................ 10 - 12 - 2013 22........................ 10 - 12 - 2013 23........................ 10 - 12 - 2013 24........................ 10 - 12 - 2013 25........................ 10 - 12 - 2013 26........................ 10 - 12 - 2013 27........................ 10 - 12 - 2013 28........................ 10 - 12 - 2013 29........................ 10 - 12 - 2013 30........................ 10 - 12 - 2013 31........................ 10 - 12 - 2013 32........................ 10 - 12 - 2013
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Table of Contents 1. PNEUMATIC SYSTEM INTRODUCTION...................................................6
4. GROUND PNEUMATIC CONNECTOR CHECK VALVE.............................42
2. GENERAL..................................................................................................8 2.1. Component Locations...........................................................................10 2.2. Controls and Indication.........................................................................12
5. BLEED AIR ISOLATION VALVE...............................................................44 5.1. Isolation Valve Control..........................................................................46
3. ENGINE BLEED AIR. ..............................................................................14 3.1. Functional Description..........................................................................14 3.2. Bleed Air Check Valve (5th Stage).........................................................16 3.3. High Stage Regulator/Valve...................................................................18 3.4. BAR and PRSOV....................................................................................22 3.5. Thermostat 232°C (450°F)....................................................................24 3.6. Overtemperature Switch – 254°C (490°F). ...........................................28 3.7. Bleed Air Control Circuit.......................................................................30 3.8. Bleed Air Precooler System....................................................................32 3.9. Precooler...............................................................................................34 3.10. Precooler Control Valve.......................................................................36 3.11. Precooler Control Valve Sensor 199°C (390°F). . .................................36 3.12. WTAI Solenoid Valve...........................................................................38 3.13. Precooler System Functional Description..............................................40
6. APU BLEED SYSTEM..............................................................................48 6.1. APU Bleed Air Valve. ............................................................................50 6.2. APU Pressure Relief Valve......................................................................52 7. PNEUMATICS DUCTS.............................................................................54 7.1. Duct Insulation.....................................................................................56 8. INDICATING AND WARNING.................................................................58 8.1. Pressure Indicating................................................................................58 8.2. Bleed Trip Off........................................................................................60 8.3. Dual Bleed Light...................................................................................62
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List of Illustrations 232°C (450°F) THERMOSTAT.................................................................................................. 25 254°C (490°F) OVERTEMPERATURE SWITCH . ....................................................................... 29 APU BLEED AIR VALVE............................................................................................................ 51 APU BLEED SYSTEM................................................................................................................ 49 APU PRESSURE RELIEF VALVE.................................................................................................. 53 BAR, 232°C THERMOSTAT & PRSOV - SCHEMATIC................................................................. 27 BAR AND PRSOV.................................................................................................................... 23 BLEED AIR CHECK VALVE (5th stage)................................................................................... 17 BLEED AIR CONTROL CIRCUIT................................................................................................. 31 BLEED AIR ISOLATION VALVE.................................................................................................. 45 BLEED AIR ISOLATION VALVE CONTROL.................................................................................. 47 BLEED AIR PRECOOLER SYSTEM.............................................................................................. 33 BLEED TRIP OFF SCHEMATIC................................................................................................... 61 COMPONENT LOCATIONS...................................................................................................... 11 CONTROLS AND INDICATION.................................................................................................. 13 DUAL BLEED SCHEMATIC....................................................................................................... 63 DUCT INSULATION.................................................................................................................. 57 ENGINE BLEED AIR ( L ENG SHOWN)....................................................................................... 65 ENGINE BLEED AIR - GENERAL................................................................................................ 15 functional SCHEMATIC...................................................................................................... 21 GROUND PNEUMATIC CONNECTOR CHECK VALVE................................................................ 43 HIGH STAGE REGULATOR/VALVE............................................................................................. 19 high stage regulator/valve ........................................................................................... 21 PNEUMATIC DUCTS................................................................................................................ 55 PNEUMATIC PRESSURE INDICATION........................................................................................ 59 PNEUMATIC SYSTEM ............................................................................................................... 7 PNEUMATIC SYSTEM - BLOCK DIAGRAM................................................................................. 9 PRECOOLER............................................................................................................................ 35 PRECOOLER CONTROL VALVE................................................................................................. 37 PRECOOLER SYSTEM FUNCTIONAL SCHEMATIC..................................................................... 41 SOURCES AND USERS............................................................................................................... 7 WTAI SOLENOID VALVE........................................................................................................... 39
Abbreviations and Acronyms ACAU APU BAR BAV °C °F PCCV PRSOV WTAI solen. vlv.
Air Conditioning Accessory Unit Auxiliary Power Unit Bleed Air Regulator Bleed Air Valve Degrees Centigrade Degrees Farenheit Precooler Control Valve Pressure Regulator and Shutoff Valve Wing Terminal Anti-Ice Solenoid Valve
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B737NG/36/301 Pneumatic System
1. PNEUMATIC SYSTEM INTRODUCTION. The purpose of the pneumatic system is to supply compressed air for a controlled temperature and pressure environment during all phases of flight and ground operation. Air is obtained from engine bleeds, auxiliary power unit or ground sources and distributed through a system of ducts to the using systems. System description. The pneumatic system controls engine bleed air source, temperature, and pressure. The pneumatic system provides high temperature, high pressure air for : - Air conditioning pressurization, - Wing and cowl thermal anti-icing, - Potable water system, - Hydraulic system and - Engine starters.
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ELECTRICAL 115V AC 28V DC, 28V AC
AIR CONDITIONING & PRESSURIZATION
ENGINE
A.P.U.
FLOW & TEMPERATURE CONTROLLED AIR USED BY :
PNEUMATIC SYSTEM
WING & COWL THERMAL A/ICE
ENGINE STARTING GROUND CART • WATER PRESSURIZATION • HYDRAULIC SYSTEM
PNEUMATIC SYSTEM SOURCES AND USERS
ELECTRICAL CONTROL SIGNALS
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B737NG/36/301 Pneumatic System
2. GENERAL. The pneumatic system supplies hot high pressure air to the systems on the airplane that use air.
APU Bleed Air System. The APU load compressor supplies bleed air on the ground and in the air.
These use the sources of pneumatic power :
Pneumatic Ground Air Connection. The pneumatic ground air connection provides for the connection at a ground pneumatic cart. The pneumatic cart car supply bleed air for engine start and ground use at the air conditioning system.
- Engine bleed air, - APU - Ground source. Engine Bleed Air. There is one bleed air system for each engine. The engine bleed system controls bleed air temperature end pressure. Engine bleed air comes from the 5th and 9th stages of the high pressure compressor. A high stage regulator and high stage valve control the flow of 9th stage bleed air. The 5th stage check valve prevents reverse flow into the 9th stage. At low engine speeds, bleed air comes from the 9th stage. At high engine speeds, bleed air comes from the 5th stage. A bleed air regulator and the pressure regulator and shutoff valve (PRSOV) control the flow at bleed air to the pneumatic manifold. ACAU. The air conditioning accessory unit (ACAU) contains relays, and is an interface between the air conditioning/bleed air controls panel switches and lights.
Pneumatic Manifold System. The pneumatic manifold system gets bleed air from the engines, APU, or pneumatic ground cart. A bleed air isolation valve divides the pneumatic manifold into leg and right sides. The normal position at this valve is closed. Because at this, a single duct failure cannot cause a loss at pressure to the whole pneumatic manifold. The pneumatic manifold has two pressure transmitters. One transmitter is on the right side of the manifold and the other is on the left side. They measure the manifold pressures. Pressure indication is so the air conditioning panel. The right side at the manifold has a pneumatic ground air connector. Controls and Indications. The air conditioning/bleed air controls panel has control switches and lights to control and monitor the pneumatic system.
Engine Bleed Air Precooler System. The precooler system controls the engine bleed air temperature. The precooler control valve, precooler control valve sensor, and WTAI solenoid valve control the flow at fan air to the precooler.
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ON -800 ONLY
HYD RSVR
PRESS XMTR
WING A/I
ISO VALVE
WING A/I
1 HYD RSVR
ENG START
PRECOOLER CTL. VLV. SENS. 199¡C/227¡C
ENG START
WATER TANK
THERMOSTAT 232¡C
OVHT SW. 254¡C
±200¡C
GND CONNECTOR PACK 2
PACK 1
±200¡C
PRECOOLER
PRECOOLER
2
2
RELIEF VALVE
±45 psi PRECOOLER CTL VALVE
±45 psi APU BLEED VALVE
PRSOV
PRECOOLER CTL VALVE
PRSOV
±34 psi
±34 psi TO NOSE COWL A/ICE
TO NOSE COWL A/ICE
A.P.U. HSV
APU ECU
CONTROL PANEL P5 HSV
1
ON -800 ONLY
2
“PACK TRIP OFF” LIGHT ON -6 & 700
E6
FAN IP 5th ST ENGINE 1
ACAU
HP 9th ST
FAN
ACAU : AIRCO ACCESS UNIT ECU : ELECTRONIC CTL UNIT HSV : HIGH STAGE VALVE PRSOV : PRESS REG. SHUT OFF VALVE
IP 5th ST ENGINE 2
ACAU E4-1
PNEUMATIC SYSTEM - BLOCK DIAGRAM
HP 9th ST 232¡C = 450¡F 199¡C/227¡C = 390¡F/440¡F 254¡C = 490¡F
E4-1
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2.1. Component Locations. Engine Bleed air. The engine bleed system components are on the engine compressor cases and in the engine struts. Pneumatic Manifold. The pneumatic manifold (crossover duct) is in these areas :
B737NG/36/301 Pneumatic System
Controls and lndication. The pneumatic system controls and indications are on the P5-10 air conditioning panel in the flight compartment. The air conditioning accessory units (ACAU’s) are the interface between airplane logic and the pneumatic system. The ACAU’s are in the EE compartment.
- The leading edges of the wing inboard of the Engine struts, - The crossover duct is in the forward areas of the Air conditioning pack bays, - The keel beam. APU Bleed Air. The APU and the APU bleed system components are in a torque box in the 48 section. The APU bleed air duct is in these areas : - Along the right side of the APU torque box, - Through section 48 and the aft pressure bulkhead, - Along the left side and forward bulkhead of the Aft cargo compartment, - In the keel beam.
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COMPONENT LOCATIONS page 11 10 - 12 - 2013 rev : 4
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2.2. Controls and Indication. DUAL BLEED Light. Illuminated (amber) : APU bleed air valve open and engine N° 1 BLEED air switch ON, or engine N° 2 BLEED air switch ON, APU bleed air valve and isolation valve open. Bleed Air DUCT PRESSURE Indicator. Indicates pressure in L and R (left and right) bleed air ducts. Air Conditioning PACK Switch. OFF : pack signalled OFF. AUTO : - with both packs operating. each pack regulates to low flow, - with one pack operating, operating pack regulates to high flow in flight with flaps up, - when operating one pack from APU (both engine BLEED air switches OFF), reaulates to high flow. HIGH : - pack regulates to high flow, - provides maximum flow rate on ground with APU BLEED air switch ON. ISOLATION VALVE Switch. CLOSE : closes isolation valve. AUTO : - closes isolation valve if all engine BLEED air and air conditioning PACK switches ON, - opens isolation valve automatically if either engine BLEED air or air conditioning PACK switch positioned OFF. OPEN : opens isolation valve.
B737NG/36/301 Pneumatic System
Engine BLEED Air Switches. OFF : closes engine bleed air valve. ON : opens engine bleed air valve when engines are operating. APU BLEED Air Switch. OFF : closes APU bleed air valve. ON : opens APU bleed air valve when APU is operating. PACK TRIP OFF Light. Illuminated (amber) : - indicates pack temperature has exceeded limits, - related pack valve automatically closes and mix valves drive full Cold, - requires reset. WING-BODY OVERHEAT Light. Illuminated (amber) : - left light indicates overheat from bleed air duct leak in left engine strut, left inboard wing leading edge, left air conditioning bay, keel beam or APU bleed air duct - right light indicates overheat from bleed air duct leak in right engine strut, right inboard wing leading edge or right air conditioning bay. BLEED TRIP OFF Light. Illuminated (amber) : excessive engine bleed air temperature or pressure, - related engine bleed air valve closes automatically, - requires reset. Wing-Body Overheat (OVHT) TEST Switch. Push : - tests wing-body overheat detector circuits - illuminates both WING-BODY OVERHEAT lights. TRIP RESET Switch Push (if fault condition is corrected) : - resets BLEFD TRIP OFF, PACK TRIP OFF and DUCT OVERHEAT lights - lights remain illuminated until reset. page 12 10 - 12 - 2013 rev : 4
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CONTROLS AND INDICATION page 13 10 - 12 - 2013 rev : 4
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3. ENGINE BLEED AIR. The engine bleed air distribution system supplies temperature and pressure regulated air to the bleed air manifold.
3.1. Functional Description. The pressure regulator and shutoff valve (PRSOV) controls the flow of engine bleed air to the pneumatic manifold. The bleed air regulator (BAR) operates the PRSOV with control pressure. The source of pressure for the bar is the engine bleed interstage duct. The BAR gets electrical control from a 28V DC signal. This signal comes from the air conditioning accessory unit (ACAU). When the BAR solenoid valve opens electrically, it supplies control pressure to open the PRSOV against spring force. When the BAR closes electrically, it bleeds the control pressure from the PRSOV. Spring force closes the PRSOV. Usually, the engine bleed switch controls the BAR. In the ON position, the switch supplies a signal through the ACAU to open the solenoid valve in the BAR. In the OFF position, the switch supplies a signal to close the solenoid valve in the BAR. When the engine fire switch is in the normal (down) position, it arms the engine bleed switch. When the engine fire switch is in the FIRE (up) position, it sends a signal to close the BAR solenoid valve. This causes the PRSOV to close. This happens regardless of the bleed switch position. There is protection so that the engine bleed air manifold will not have reverse flow during engine starts. The engine start valve sends a signal to the ACAU during engine start. This causes the ACAU to send a close signal to the BAR solenoid valve, regardless of the bleed switch position.
There is protection for the pneumatic manifold from overpressure or overtemperature conditions. Operation of either the 180/220 psi overpressure switch or the 254°C (490°F ) overheat switch will cause a bleed trip off condition. A bleed trip off condition sends a signal from the ACAU to close the bar sole- noid valve regardless of bleed switch position. 5th and 9th Stage Engine Bleeds. Bleed air comes from the 5th and 9th stages of the engine high stage compressor. At low engine speed, 5th stage air is not sufficient for the pneumatic system demands and the 9th stage supplies bleed air. At high engine speed the high stage valve closes, and the 5th stage supplies bleed air. The high stage regulator controls the high stage valve. High stage valve operation is automatic. Engine Bleed Air Cooling Functional Description. A precooler system cools engine bleed air. The precooler system is automatic. The precooler system keeps engine bleed air temperatures between 199°C (390°F) and 229°C (440°F). The precooler is a cross flow heat exchanger. It uses engine fan air to cool the engine bleed air. The precooler control valve controls fan air flow to the precooler. The pre- cooler control valve modulates in response to these components : - The precooler control valve sensor, - The wing thermal anti-ice (WTAI) solenoid valve. The 232°C (450°F) thermostat bleeds control pressure from the PRSOV if engine bleed air downstream of the precooler is 232°C (450°F) or higher. This causes the PRSOV to modulate toward closed. The reduced airflow through the PRSOV has these effects : - Prevents bleed trip off conditions, - A drop in pneumatic manifold pressure. page 14 10 - 12 - 2013 rev : 4
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B737NG/36/301 Pneumatic System
ENGINE BLEED AIR - GENERAL
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3.2. Bleed Air Check Valve (5th Stage). The 5th stage bleed air check valve prevents 9th stage bleed air flow into the 5th stage bleed port. Physical Description. The bleed air check valve is a split-flapper check valve. Location. The bleed air check valve is part of the engine bleed air manifold. It is on the left side of the engine high pressure compressor case. Functional Description. The valve lets air flow go in the direction of the arrow. It stops air flow in the opposite direction. Two semicircular flappers control air flow. Normal airflow opens the flappers. Reverse airflow closes the flappers. Training Information Point Install the bleed air check valve so that the flow arrow points away from the 5th stage bleed port. Align the flange clamps correctly and torque to specifications. Improperly aligned or loose clamps may interfere with engine components or the inner thrust reverser cowls.
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ENGINE LEFT SIDE
BLEED AIR CHECK VALVE (5th STAGE)
BLEED AIR CHECK VALVE (5th stage) page 17 10 - 12 - 2013 rev : 4
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3.3. High Stage Regulator/Valve. The high stage regulator controls the high stage valve. The high stage valve controls the flow of bleed air from the 9th stage engine bleed air manifold. Valve. The operation of the high stage valve is automatic. The stage regulator controls the valve. There are no operational controls. The high stage valve is a butterfly type that spring loads to the close position. The valve opens pneumatically. A relief valve on the high stage valve bleeds off any high pressures (160 psi nominal) in the engine bleed air manifold. Air leakage around the seals of a closed high stage valve increases this pressure when there is no downstream use of bleed air. The high stage valve has a visual position indicator. Training Information Point. Remove the relief valve to get access to a test port. The high stage valve has a manual lockout. The lockout is a sliding collar on the butterfly plate shaft. A lock screw on the collar holds the collar in the locked or unlocked position. The valve can only be locked out in the closed position. Only air from the 5th stage compressor bleed port is available with the high stage valve in this position.
B737NG/36/301 Pneumatic System
Regulator. The high stage regulator controls the pressure of an unregulated air source. The unregulated air source is a tap from the 9th stage engine bleed air manifold. It supplies regulated air to the actuator of the high stage valve. The high stage regulator has a pressure relief valve as a fail-safe device. If the regulator mechanism fails, the pressure relief valve will act as a bleed-off pressure regulator. The high stage regulator keeps the high stage valve closed during engine starts. A sense line to the engine starter duct supplies pressure to the regulator. When pressure in the starter duct is more than pressure from the 9th stage tap, a reverse flow shutoff operates. This bleeds air from the actuator line. The high stage valve will then close because of spring force. A pneumatic shutoff mechanism increases the life of the bleed air regulator. This shutoff operates after the shift to 5th stage engine bleed air occurs. High pressure (110 psi nominal) in the supply port operate a pneumatic shutoff mechanism. The shutoff mechanism closes the regulator inlet, and releases air from the regulator. This reduces the duty cycle of the regulator, and sup- plies protection when pressures and temperatures are not correct. Training Information Point. The high stage regulator has test ports. The ports let you use test equipment without removal of the sense lines.
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B737NG/36/301 Pneumatic System
HIGH STAGE REGULATOR ENGINE LEFT SIDE
HIGH STAGE VALVE
HIGH STAGE REGULATOR/VALVE page 19 10 - 12 - 2013 rev : 4
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Functional Description. The high stage regulator and valve control the supply of high stage engine bleed air. The high stage regulator operates the high stage valve. The high stage valve controls the flow of bleed air from the 9th stage bleed air manifold. The high stage regulator gets unregulated air from a tap on the 9th stage bleed air manifold. The unregulated air goes through the pneumatic shutoff mechanism to the reference pressure regulator. The reference pressure regulator decreases the pressure to a constant control pressure. A relief valve prevents damage to the high stage valve if the reference pressure regulator fails.
B737NG/36/301 Pneumatic System
When 9th stage pressure is more than 110 psi, the pneumatic shutoff mechanism in the high stage regulator operates. When the pneumatic shutoff mechanism operates, this occurs: - 9th stage pressure to the reference pressure regulator is shut off - Control pressure to the high stage valve bleeds off - High stage valve closes. A relief valve in the high stage valve decreases downstream pressure in the interstage duct when the pressure regulator and shutoff valve (PRSOV) is closed. Operational Controls. The operation of the high stage bleed system is automatic and self-regulating. There are no external controls.
The control pressure from the high stage regulator goes to chamber A of the high stage valve. The actuator opens the valve against spring force and pressure in chamber B. The combination of forces that operate on the actuator cause the valve to regulate the downstream pressure to 32 psi (nominal). During normal operation, the high stage valve closes for these reasons: - Downstream pressure is more than 9th stage pressure - 9th stage pressure is more than 110 psi. When downstream pressure is more than 9th stage pressure, the reverse flow mechanism in the high stage regulator opens and bleeds off the control pressure to the high stage valve. The high stage valve then closes.
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high stage regulator/valve functional SCHEMATIC page 21 10 - 12 - 2013 rev : 4
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3.4. BAR and PRSOV. The BAR (Bleed Air Regulator) operates the PRSOV (Pressure Regulator and Shutoff Valve). The PRSOV controls the flow of bleed air from the engine. These are the PRSOV control functions : - Shutoff of engine bleed air, - Pressure regulation of engine bleed air (45 psi max), - Temperature limitation of engine bleed air (232°C/450°F).
Operation. The BAR has electrical control by signals from these devices : - The P5 panel engine BLEED switch, - The P8 panel engine fire switch, - ACAU (M324). During normal operations, the engine BLEED switch ON tells the BAR solenoid valve to open. The engine BLEED switch OFF tells the BAR solenoid valve to close. When the fire switch is up, it signals the BAR solenoid valve to close.
Physical Description. The BAR has these parts : - Mechanical latching solenoid valve, - Pressure relief valve, - 180/220 psi overpressure switch, - Ports for supply and control air lines. The PRSOV has these parts : - Pneumatic actuator, - Manual override and position indicator, - Control air port, - Downstream sense port.
Relays in the ACAU control the BAR solenoid valve to close for these conditions : - Engine start valve open (reverse flow protection), - Engine bleed trip off conditions (254°C/490°F overheat or 180/220 psi overpressure protection). The PRSOV is pneumatically controlled by the BAR. Training Information Point. The PRSOV has a manual override and position indicator. You can manually lock the valve in the closed position only.
Location. The BAR is at the 11:00 position on the engine core area and immediately aft of the fan frame. The PRSOV is at the 10:00 position on the engine core area and below the oilcooler.
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ENGINE LEFT SIDE BLEED AIR REGULATOR
PRESSURE REGULATOR AND SHUTOFF VALVE
BAR AND PRSOV page 23 10 - 12 - 2013 rev : 4
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3.5. Thermostat 232°C (450°F). The 232°C (450°F) thermostat bleeds off the pressure that operates the pressure regulator and shutoff valve (PRSOV). This occurs when engine bleed air temperature goes above 232°C (450°F). The 232°C (450°F) thermostat supplies the PRSOV a temperature control function. Physical Description. The 232°C (450°F) thermostat has these parts : - Ball valve assembly with a sense line connection, - Mounting flange with index pin, - Shielded sensor section. Location The 232°C (450°F) thermostat is in the engine bleed air strut duct. Access is through a strut access panel. Functional Description. The 232°C (450°F) thermostat operates by thermal expansion. The thermostat sensor is in the bleed air duct downstream of the precooler. This portion of the thermostat has oil filled coils. As the oil expands, it pushes a ball valve, in the upper part of the thermostat, open. The higher the duct temperature, the greater the oil expansion, and the more the ball valve opens. The 232°C (450°F) thermostat starts to open at 232°C (450°F) and is full open by 254°C (490°F).
B737NG/36/301 Pneumatic System
The open valve bleeds operating pressure from the prsov. This causes the prsov to move toward closed by spring force. The not fully open prsov reduces the mass flow of bleed air. The lower mass flow of bleed air has these effects : - Reduces the load on the precooler, - Delays a 254°C(490°F) overtemperature bleed trip off condition, - Causes duct pressure to decrease. The precooler system normally controls engine bleed air temperature to 199227°C (390-440°F). The 232°C (450°F) thermostat supplies a temperature limit function to the PRSOV. Temperature limit is for these conditions : - Use of the wing thermal anti-ice system under high ambient, temperatures or high altitudes, - Single component failures in the bleed system, - Transient conditions. Training Information Point. Nonstop operation of the 232°C (450°F) thermostat, (and the resultant low duct pressures), may result from a dirty or clogged precooler. It can also be a defective precooler control system.
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B737NG/36/301 Pneumatic System
232°C (450°F) THERMOSTAT
ENGINE STRUT ACCESS (ACCESS PANEL REMOVED)
232°C (450°F) THERMOSTAT page 25 10 - 12 - 2013 rev : 4
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B737NG/36/301 Pneumatic System
Functional Description. The BAR, PRSOV, and 232°C (450°F) thermostat regulate bleed air pressure and temperature. The BAR gets unregulated air from the interstage manifold. The unregulated air goes to the overpressure switch and to the reference pressure regulator. The reference pressure regulator reduces the pressure to a constant control pressure. Control pressure then goes to a relief valve and a latching solenoid. The relief valve opens to bleed off excess pressure from the reference pressure regulator. The latching solenoid controls the flow of control air to chamber A of the PRSOV actuator and the 232°C (450°F) thermostat bellows assembly. Control air to chamber A opens the PRSOV. Opening the PRSOV provides bleed air to the downstream sensing line and 232°C (450°F) thermostat sensing element. The downstream sensing line supplies bleed air to chamber B that also has a spring. The 232°C (450°F) thermostat bleeds off control air to chamber A of the PRSOV if bleed air temperature reaches 450F. The combination of forces acting on the actuator cause these responses from the valve : - When pressure downstream of the valve is less than 45 psig the valve is open - When pressure downstream of the valve increases, the valve modulates to limit downstream pressure to a maximum of 45 psig (nominal) - When the latching solenoid in the BAR is energized closed the PRSOV closes - When downstream temperature gets to 232°C (450°F), the PRSOV reduces the amount of bleed air to the precooler. The overpressure switch functions as a safety device. If supplly air to the BAR gets to 180/220 psi, the switch closes and causes a bleed trip off condition.
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BAR, 232°C THERMOSTAT & PRSOV - SCHEMATIC page 27 10 - 12 - 2013 rev : 4
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3.6. Overtemperature Switch – 254°C (490°F). The 254°C (490°F) overtemperature switch protects the pneumatic manifold from overheat conditions. Physical Description. The 254°C (490°F) overtemperature switch has these parts : - Wrenching flats, - Mounting threads, - Sensor, - Electric connector. Location The 254°C (490°F) overtemperature switch is on the engine bleed air strut duct, downstream of the precooler. To get access to the switch, remove the left strut access panel.
B737NG/36/301 Pneumatic System
Functional Descriotion. The 254°C (490°F) overtemperature switch operates by thermal expansion. As the temperature of the sensor increases, internal parts expand. If the temperature is more than 254°C (490°F) (nominal), the expansion of the internal parts closes switch contacts. When the switch cools, the contacts open. The 254°C (490°F) overtemperature switch monitors the temperature of engine bleed air downstream of the precooler. Normally the precooler system cools engine bleed air to199-227°C (390-440°F). At 232°C (450°F), the 232°C (450°F) thermostat reduces engine bleed air flow to reduce the precooler load. If the temperature downstream of the precooler is more than 254°C (490°F), the 254°C (490°F) overtemperature switch operates. The switch supplies a ground to an overheat relay in the air conditioning accessory unit (ACAU). The energized relay shuts down the engine bleed air system in these ways : - The solenoid valve on the bleed air regulator (BAR) closes, - The P5-10 panel BLEED TRIP OFF light comes on, - The ACAU overheat relay makes a latch circuit through the P5-10 panel TRIP/RESET switch. Training Information Point Replace the old switch packing ring with a new ring when you repLace the switch. Apply a thin layer of antiseize compound to the mounting threads of the switch before you install it. The combination of mounting thread forces and high duct temperatures can cause uncoated valve mounting threads to seize in their mounting boss.
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254°C (490°F) OVERTEMPERATURE SWITCH
ENGINE STRUT ACCESS (ACCESS PANEL REMOVED)
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3.7. Bleed Air Control Circuit. The engine bleed air control and indication circuits use 28V DC. The engine fire switch has the override authority in the control circuit. If the handle is up (fire condition), the bleed air control signal closes the bleed air regulator solenoid valve. If the engine fire switch is down (normal condition), it arms the engine BLEED switch on the air conclitioning/bleed air controls panel. When the engine BLEED switch is OFF, the control signal closes the bleed air regulator solenoid valve. When the engine BLEED switch is ON, the control signal goes through relaxed relays (normal conditions) in the air conditioning accessory unit (ACAU). This opens the bleed air regulator solenoid valve. The relays in the ACAU protect the bleed air system during these conditions : - Engine start operations, - Engine bleed air interstage duct overpressure, - Engine bleed air overtemperature. The start relay energizes when the engine start valve opens. The energized relay contacts send a signal to close the bleed air regulator solenoid valve. The overheat relay energizes when a bleed trip off condition exists. These conditions cause a bleed trip off :
B737NG/36/301 Pneumatic System
The contacts of an energized ACAU overheat relay cause these operations : - The bleed air control signal closes the bleed air regulator solenoid valve, - The air conditioning/bleed air controls panel BLEED TRIP OFF light comes on, - The P7 MASTER CAUTION and AIR COND annunciator lights come on, - A holding circuit connects through the air conditioning panel TRIP RESET push-button switch. To get control of the engine bleed system after a bleed trip off, these conditions must occur : - The overpressure or overtemperature switch must return to its normal (open) condition, - You must push the air conditioning panel TRIP RESET push-button switch (to break the holding circuit). The air conditioning panel engine BLEED switch has multiple poles. One set of poles controls the solenoid valve circuit. Another set of poles supplies discrete signals to the flight management computer. The open and close coils on the bleed air regulator solenoid valve are constant duty coils. The solenoid valve also has a mechanical latch. When there is a loss of electric power, the solenoid valve will stay in the last electrically commanded position.
- 180/220 psi overpressure switch operation, - 254°C (490°F) overtemperature switch operation.
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3.8. Bleed Air Precooler System. The bleed air precooler system controls the temperature of the engine bleed air before it goes into the pneumatic manifold. General. The precooler control valve spring loads to the full open position. With the engine in operation, pressure from the interstage bleed duct is available to the precooler control valve. The valve regulator reduces the pressure to a control pressure and the actuator moves the precooler control valve closed. The precooler control valve sensor 199°C (390°F), in the engine strut duct, senses bleed air temperature downstream of the precooler. When the duct temperature reaches 199°C (390°F) the sensor starts to bleed air pressure from the precooler control valve. This causes the control valve to move toward open by spring force. This supplies cooling air to the precooler.
B737NG/36/301 Pneumatic System
When you operate the WTAI system on the ground, the WTAI solenoid valve energizes. Under these conditions, the WTAI solenoid valve controls the precooler control valve movement. This opens the WTAI solenoid valve and bleeds off the pressure that goes to the precooler control valve. This causes the valve to go full open. The full open precooler control valve supplies maxi- mum fan airflow to the precooler. This protects the slats from possible damage by the hot bleed air. See the ice and rain chapter for more information on the WTAI solenoid valve (ATA 30). Operation. Operation of the precooler system is automatic and requires no crew action. A position indicator on the precooler control valve shows valve position.
The higher the temperature at the precooler control valve sensor, the more control air it bleeds from the precooler control valve actuator. This causes the precooler control valve to open further, and more cooling fan air reaches the precooler. The engine fan airflow to the precooler keeps engine bleed air temperature in limits. The precooler system keeps the temperature of engine bleed air to 199-227°C (390-440°F) as it goes into the pneumatic manifold. The WTAI solenoid valve also controls the pressure in the precooler control valve actuator. The WTAI solenoid operates a ball valve. It spring loads closed and opens when energized. With the solenoid deenergized, the WTAI solenoid valve stays closed. Under these conditions the precooler control valve sensor controls the precooler control valve movement.
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PRECOOLER CONTROL VALVE
WTAI SOLENOID VALVE
OPEN
A/C ON GROUND WTAI SELECTED ON (TEST)
FAN AIR
ENGINE 1
5th STAGE PRECOOLER CONTROL VALVE SENSOR 199°C - 227°C (390°F- 440°F)
9th STAGE
PRECOOLER ENGINE BLEED AIR MANIFOLD INTERSTAGE DUCT
NOTE : LEFT SYSTEM SHOWN, RIGHT SYSTEM EQUIVALENT
TO PNEUMATIC MANIFOLD
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3.9. Precooler. The precooler cools engine bleed air before it goes to the pneumatic manifold. Physical Description. The precooler is an air to air heat exchanger. Location The precooler is on the top of the engine high pressure compressor case. Functional Description. The precooler supplies a large surface area for efficient heat transfer from the bleed air to the fan air (heat sink). As the engine bleed air moves through the precooler, the bleed air gives up heat to the walls of the precooler. The walls are made of plates and fins. Engine fan air that goes through the precooler on the other side of the walls, removes the heat and carries it away. Heat transfer goes from the bleed air, to the precooler walls, to the fan air. The fan air then flows over the engine case and overboard through the case vents. A sense line connection connects to the pressure regulating and shutoff valve and the high stage regulator. See the engine bleed air section for more information on the pressure regulating and shutoff valve and high stage regulator. Training Information Point. The precooler uses narrow passages with thin walls and cooling fins for efficient heat exchange. Contamination or obstruction of the precooler passages decreases or prevents airflow and heat transfer. Keep the precooler clean for maximum performance.
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ENGINE LEFT SIDE
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3.10. Precooler Control Valve. The precooler control valve controls the flow of fan air to the precooler. Physical Description. The precooler control valve is a spring-loaded open butterfly valve. It is a pneumatically controlled and actuated valve. These are the parts of the precooler control valve : - Manual override and position indicator, - Sense line to precooler control valve sensor, - Sense line to wing thermal anti-ice solenoid valve, - Supply pressure line (from interstage manifold), - Actuator. Location. The precooler control valve is on top of the engine forward of the precooler. Training Information Point. The precooler control valve has a manual override and position indicator. The override is used to verify the valve is spring loaded open.
3.11. Precooler Control Valve Sensor 199°C (390°F). The precooler control valve sensor 199°C (390°F) controls the movement of the precooler control valve. Physical Description. The precooler control valve sensor 199°C (390°F) has these parts : - Ball valve assembly, - Sense line connection, - Mounting flange with indexing pin, - Shielded sensor section.
B737NG/36/301 Pneumatic System
Location The precooler control valve sensor is in the engine bleed air strut duct. Access is through a strut access panel. Functional Descriotion. The precooler control valve sensor is a bleed-off thermostat. It operates by thermal expansion. The operation of the precooler control valve sensor is automatic. Crew action is not necessary. The lower part of the sensor is in the bleed air duct downstream of the precooler. This portion of the sensor has oil-filled sense coils. As heat causes the oil to expand, it pushes a ball valve in the upper part of the sensor to open. The higher the duct temperature, the greater the oil expansion, and the more the ball valve opens. The sensor ball valve starts to open at 199°C (390°F) and is full open at 227°C (440°F) (nominal values). The open sensor ball valve bleeds off pressure to operate the precooler control valve actuator. This causes the precooler control valve to move toward open by spring force. The precooler control valve sensor can control the movement of the precooler control valve. The precooler control valve sensor operates in parallel with the wtai solenoid valve to control the precooler control valve. The energized WTAI solenoid valve bleeds off all of the pressure that operates the precooler control valve. The precooler control valve temperature sensor does not have any effect for this operation. The WTAI makes sure that bleed air will receive maximum cooling for ground operations of the WTAI system. See the ice and rain chapter for more information on the WTAI solenoid valve (ATA 30)
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PRECOOLER CONTROL VALVE
B737NG/36/301 Pneumatic System
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3.12. WTAI Solenoid Valve. The wing thermal anti-ice (WTAI) solenoid valve bleeds actuator pressure from the precooler control valve. The WTAI solenoid valve operates when you use the wing thermal anti-icing system on the ground. Location. There are two WTAI solenoid valves, one for each bleed air precooler system. The valves are on top of the compressor section of each engine. General. The wing thermal anti-icing system prevents ice formation on the wing leading edge during ground operations and in flight. During flight there is a large airflow over the wing. This airflow has a great cooling effect on the leading edges. The wing thermal anti-icing system heat output is great enough to overcome this cooling effect.
B737NG/36/301 Pneumatic System
During ground operations of the wing thermal anti-icing system, the wing anti-ice control module (P5-11) energizes the WTAI solenoid valves. This opens the solenoid valves. The solenoid valves bleed actuating pressure from the precooler control valve. This causes the precooler control valves to go wide open. The wide open precooler control valve gives maximum cooling to the engine bleed air. This protects the wing leading edges from overheat damage. The WTAI solenoid valves cause the precooler control valves to go wide open, regardless of the precooler control valve sensor conditions. For more information about the WTAI solenoid valve, see ice and rain protection (chapter 30).
When the wing thermal anti-icing system is used on the ground, there is very little cooling airflow over the wing. In these conditions, the wing thermal antiicing system heat output can overheat the wing leading edges. This can ruin the temper of the leading edges devices. The precooler system gives maximum cooling to the engine bleed air during ground operations to prevent overheat damage to the slat temper. Functional Description.
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WTAI SOLENOID VALVE
ENGINE LEFT SIDE
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3.13. Precooler System Functional Description. The precooler system controls the temperature of the bleed air to the pneumatic manifold. The precooler control valve gets unregulated air pressure from the interstage manifold. The unregulated air pressure goes to the actuator reference pressure regulator and the servo reference pressure regulator. The actuator reference pressure regulator reduces the pressure to a constant control pressure. Control pressure then goes to chamber A and the nozzle. The servo reference pressure regulator reduces the pressure to a constant control pressure. Control pressure then goes to chamber B of the servo, precooler control valve sensor, and WTAI solenoid valve.
B737NG/36/301 Pneumatic System
The precooler control valve sensor starts to open when the temperature in the pneumatic duct is 390F and is full open at 440F. This decreases the pressure in chamber B. As pressure in chamber B decreases, the lever on the servo opens the nozzle. The open nozzle decreases pressure in chamber A and the spring in the precooler control valve actuator moves the valve to open. As the precooler control valve opens, a feedback spring starts to move the lever to close the nozzle. This prevents rapid movement of the precooler control valve. The WTAI solenoid valve is open when the airplane is on the ground and the wing thermal anti-ice system is on. This decreases all the pressure in chamber B, and moves the lever to open the nozzle. The open nozzle then decreases all the pressure in chamber A. Then the spring in the actuator opens the precooler control valve full open.
The control pressure in chamber A opens and closes the precooler control valve. When pressure increases, the precooler control valve moves towards close. When pressure decreases, the precooler control valve moves towards open. The control pressure in chamber B moves the lever on the servo. When control pressure increases, the lever closes the nozzle. When control pressure decreases, the lever opens the nozzle. The control pressure in chamber B decreases when the precooler control valve sensor opens, or the WTAI solenoid valve opens.
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4. GROUND PNEUMATIC CONNECTOR CHECK VALVE. The ground pneumatic connector check valve lets you connect an external source of compressed air to the pneumatic manifold. It prevents flow out of the manifold, and lets flow into the manifold. General Description. The check valve is a spring-loaded closed split flapper type check valve. Also, it has a standard quick disconnect nipple-type fitting. The ground pneumatic connector check valve has these parts : - 3-inch (8-cm) quick disconnect nipple, - Internal check valve. Location. The ground pneumatic connector check valve is on the right side of the pneumatic manifold crossover duct. Access is through the small panel on the forward outboard corner of the right air conditioning bay access door. Functional Description. When an external source is pressurizing the pneumatic manifold, the force of the airflow is more than the spring force and the check valve opens. The check valve springs and manifold pressure close the valve when there is no external source. This prevents leakage from the manifold.
Training Information Point. This connector connects directly into the pneumatic manifold and supplies no temperature or pressure regulation. The external pneumatic source must control temperature and pressure within these placard limits on the connector door : - Maximum temperature 232°C (450°F) - Maximum pressure 60 psi. Before you supply air from an external pneumatic source, these conditions should be met : - Battery power on - Air conditioning pack switches off. This makes sure that the pack valves will be closed. CAUTION : MONITOR FLIGHT COMPARTMENT WING BODY OVERHEAT SYSTEM DURING ALL OPERATIONS OF THE PNEUMATIC SYSTEM. 115V AC power is necessary to operate the wing body overheat or air conditioning system(s).
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GROUND PNEUMATIC CONNECTOR CHECK VALVE ACCESS PANEL
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5. BLEED AIR ISOLATION VALVE. The bleed air isolation valve has these functions : - Separates the pneumatic manifold into right and left sides, - Connects the right and left sides of the pneumatic manifold for cross bleed operation. Physical Description. The isolation valve is a 115V, single-phase, motor operated butterfly valve. The bleed air isolation valve has a valve body and an actuator assembly. The actuator assembly has these parts : - An electric motor and drive assembly, - A manual override handle/position indicator.
Operational Controls. A three-position toggle switch on the air conditioning bleed air controls panel controls the bleed air isolation valve. These are the switch positions : - OPEN the valve opens to connect the right and left sides of the bleed air manifold. - AUTO the aircraft switch position logic controls the valve to open and close as necessary for aircraft operations. - CLOSE the valve closes to separate the right and left sides of the bleed air manifold.
Location. The bleed air isolation valve is part of the crossover duct. It is in the keel beam, in the forward area of the air conditioning bays. Functional Description. The bleed air isolation valve is a butterfly shutoff valve. A 115V AC, single phase motor operates the valve. It is reversible in transit. The valve has a manual override handle that lets you manually set the position of the valve. The manual override handle is also a position indicator. A flange in front of the lever shows OPEN and CLOSED. Indications. A visual position indicator on the valve shows the valve position.
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BLEED AIR ISOLATION VALVE (LOOKING FROM LEFT AIR CONDITIONING COMPARTMENT)
(§LOOKING DOWN)
(LOOKING FORWARD)
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5.1. Isolation Valve Control. The bleed air isolation valve uses 115V AC electrical power. A three position toggle switch on the P5-10 air conditioning panel controls the valve motor and valve position. These are the functions with the bleed air isolation valve switch in the OPEN position : - Power goes to the open coils of the valve motor, then - The valve moves to the full open position, - The valve limit switches open, and remove power from the motor. These are the functions with the bleed air isolation valve in the CLOSE position :
B737NG/36/301 Pneumatic System
When all the toggle switches are in the auto, high, or on positions, the valve closes. The control circuit shows a typical cruise condition. The bleed air isolation valve will remain closed. In this configuration, the pneumatic manifold divides into a left and right side. This prevents a single pneumatic duct failure from loss of pressure to all of the manifold. With any one of the pack or engine bleed switches in the off position, the valve opens. A trip off condition closes a pack or bleed valve, but does not change the position of its P5-10 panel control switch. The circuit uses switch position logic, not valve position logic. You must be manually put the switch in the OFF position to open the isolation valve when the its switch is in AUTO.
- Power goes to the close coils of the valve motor, then - The valve moves to the full closed position, - The valve limit switches open, and remove power from the motor. With the bleed air isolation valve switch in the AUTO position, the control of the isolation valve comes from these P5-10 switches : - R PACK switch, - L PACK switch, - ENG 1 BLEED switch, - ENG 2 BLEED switch. With the isolation valve switch in auto, these switches supply the logic to control the bleed air isolation valve position.
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6. APU BLEED SYSTEM. The apu bleed air system supplies compressed air to the pneumatic manifold: - On the ground, - In the air (up to 17,000 feet). The APU can supply power to these systems : - Engine start systems, - ECS systems. General Description. The APU load compressor is the source of the APU bleed air. The load compressor inlet guide vanes and surge control systems control the pressure and flow of the APU bleed air. The APU bleed air valve (BAV) isolates the APU load compressor from the pneumatic manifold.
Location. The APU, load compressor, and bleed air valve are in the APU compartment. The ECU is on the E6 rack in the aft cargo compartment. The P5-10 panel control module is in the flight compartment. The APU check valve is in the keel beam, between the forward air conditioning bays. Operational Displays. The APU bleed air valve has a visual position indicator on the valve assembly. These indications show valve operation : - P5-10 panel duct pressure gage, - P5-10 panel DUAL BLEED indication light.
The M1709 APU electronic control unit (ECU) controls the APU bleed air valve. The ECU receives bleed control signals from the P5-10 air conditioning control panel. The APU bleed air duct connects the APU bleed air valve to the pneumatic manifold. An APU check valve is in the APU duct. This valve protects the APU load compressor from engine bleed air flow. See the APU chapter for more information on the APU bleed air pressure control (ATA 49).
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APU BLEED AIR VALVE (ROTATED FOR CLARITY)
APU BLEED SYSTEM
APU CHECK VALVE
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6.1. APU Bleed Air Valve. This schematic shows the relationship between the APU bleed air valve and its interfaces : - APU electronic control unit (ECU), - APU load compressor, - APU pneumatic duct, - DUAL BLEED indication circuit. General Description. When the P5-10 module APU BLEED switch is in the ON position, it supplies a ground discrete to the APU ECU. A control signal from the APU ECU energizes the APU bleed air valve solenoid. The energized solenoid sends pressure from a tap upstream of the valve butterfly plate to the valve actuator. The pressure opens the valve against the valve spring. This moves the valve but- terfly plate to the wide open position.
B737NG/36/301 Pneumatic System
Airplane logic inputs to the APU ECU also have an effect on the control signals to the APU bleed air valve. These are the logic inputs : - P8-1 APU FIRE switch (UP causes an APU shutdown and the bleed air valve to close), - M279 fire detection module (FIRE causes APU shutdown and bleed air valve to close), - APU speed sensors (UNDERSPEED causes the APU bleed air valve to close), - ARINC 429 altitude (altitude above 17,000 ft causes the APU bleed air valve to close). See the APU chapter for more information on the APU bleed air valve interfaces (ATA 49).
Both of these conditions are necessary for the apu bleed air valve to to open: - A control signal from the apu ecu to energize the apu solenoid valve, - Upstream duct pressure. When the APU ECU removes the control signal from the APU bleed air valve control solenoid, the solenoid deenergizes. The de-energized solenoid bleeds the pressure from the valve actuator. The valve’s spring then pushes the valve closed. A position limit switch on the valve does these things : - Supplies vaLve position discretes to the APU ECU, - Supplies a ground input to the P5-10 module DUAL BLEED indication circuit, - Supplies visual indication of valve position.
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6.2. APU Pressure Relief Valve. The APU pressure relief valve protects the pneumatic ducts from too much pressure. This can occur if the pressure regulating function of the APU bleed system fails. Too much pressure can rupture the ducts. Location. The APU pressure relief valve is on the APU bleed air duct. It is in the section 48 stabilizer compartment under the catwalk. Functional Description. The APU pressure relief valve is a spring-loaded, air operated, pressure relief device. The spring holds the poppet closed at pressures less than 75 psi (nominal). Duct pressure more than 75 psi pushes the poppet off its seat. This opens the valve. The open valve relieves duct overpressure. When duct pressure is less than 65 psi, the spring returns the poppet to its seat. This closes the valve. Training Information Point. Remove and replace the old valve packing ring and replace it with a new packing ring when you install a new APU pressure relief valve. Before you install a new APU pressure relief valve, apply a thin layer of antiseize compound to the mounting threads of the valve. The combination of the mounting thread forces and high duct temperatures can cause uncoated valve mounting threads to seize in their mounting boss. Use the valve body wrench flats when you install the valve. Do not use a wrench on the jam nut or cap. This can have an effect on valve spring preload.
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7. PNEUMATICS DUCTS. The pneumatic manifold sends hot, compressed air through the pneumatic system.
NOTE : The duct leak overheat protection system uses 115v ac power. Without power, the system will not operate.
Physical Description. The pneumatic ducts are thin-walled tubes. The ducts have flanges at their ends and join with flange clamps.
See the wing and body overheat detection section for more information (ATA 26).
The duct sections are made short in length. This lets ducts expand when hot air flows through them. This is thermal expansion. Tension force holds the ducts between their structural mounts. Some ducts have a gold coating. The coating has these functions : - Protects the ducts from the effects of hydrocarbon contamination (hydrogen embrittlement) - Reduces heat transfer. Insulation blankets cover some ducts to reduce heat transfer. Location. Pneumatic ducts are in these areas of the airplane :
Some duct flange clamps are in areas that contain control cables or other mechanical/electrical devices. Special care must be taken so that the clamps and these components do not touch. WARNING : DO NOT REMOVE CLAMPS ON PRESSURIZED DUCTS. PERSONAL INJURY OR EQUIPMENT DAMAGE MAY OCCUR. Keep the pneumatic ducting clean and free from these types of contamination : - Oil, - Hydraulic fluid, - Fuel, - Other hydrocarbon compounds.
- Pneumatic manifold - Pneumatic systems. Training Information Point. Overheat detectors are near the pneumatic ducts. These elements operate by the hot air that comes from pneumatic duct leaks. An active element causes a WING-BODY OVERHEAT light on the air conditioning bleed air controls panel to come on.
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PNEUMATIC DUCTS
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7.1. Duct Insulation. The pneumatic manifold duct insulation decreases the heat flow from the ducts to the adjacent area.
B737NG/36/301 Pneumatic System
Functional Description. The duct insulation decreases the heat flow from the ducts they cover. This protects the airplane structure, wiring, and components adjacent to the ducts.
General Description. There are two types of pneumatic insulation on the airplane : - Soft insulation, - Hard shell insulation. Soft insulation is a soft, precut, fiberglass pad insulation that is wrapped with a cover and held with tie straps. Hard shell insulation is a hard, preformed, fiberglass lay-up, air gap insulation that is pre-shaped to fit snugly around the contour of a duct section. The hard shell insulation unit comes in two halves and attaches to the duct section with band clamps or wire lace. Location. The soft insulation is on the APU duct in the aft cargo compartment areas. The APU duct and soft insulation are behind the sidewall panels in the aft cargo compartments. The hard shell insulation is on the pneumatic ducts in the keel beam of the airplane.
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8. INDICATING AND WARNING. 8.1. Pressure Indicating. The indicating system gives the flight crew displays of the pneumatic system status. The displays show this information : - Right and left pneumatic manifold pressures - DUAL BLEED conditions. Pneumatic system indications are on the air conditioning/bleed air controls panel.
Dual Duct Pressure Indicator. The pneumatic duct pressure indicator is on the air conditioning/bleed air controls panel. The pressure indicator has two independent needles (L and R), and a single scale (0-80 psi). Integral lamps light the indicator scale. The indicator has a single electrical connector. Training Information Point The pressure indicator contains integrated circuits and is an electro static discharge sensitive device.
A dual needle (right and left) pressure indicator shows the pressure in the right and left sides of the pneumatic manifold. Duct Pressure Transducer. There are two pressure transmitters. One for each side (left and right) of the pneumatic manifold. The pressure transmitters are on the forward bulkheads of the air conditioning bays near the pneumatic crossover duct. The pressure transmitters have a pneumatic sense port on one end and an electric connector on the other. The duct pressure transducers use 28v dc and pneumatic pressure to provide a signal to the pneumatic duct pressure indicator on the air conditioning/bleed air controls panel.
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LEFT PRESSURE TRANSMITTER
CONTROL PANEL (P5)
P5 PNEU. DUCT PRESS. INDICATOR
RIGHT PRESSURE TRANSMITTER
AIR CONDITIONING BAY FORWARD BULKHEAD
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8.2. Bleed Trip Off. The BLEED TRIP OFF light shows the crew when the engine bleed system operation stops. Functional Description. There are two BLEED TRIP OFF indication systems, one for each engine bleed system. The BLEED TRIP OFF light is part of the engine bleed air control circuit. Overheat or overpressure switches will trip off (stop) the engine bleed air system. This protects airplane components from damage. Two conditions cause a BLEED TRIP OFF : - Operation of the 254°C (490°F) overheat switch, - Operation of the bleed air regulator (BAR) 180 psi overpressure switch. The overtemperature or overpressure switch supplies a ground to an overheat relay in the air conditioning accessory unit (ACAU). The overheat relay then energizes. The energized contacts of the relay do these things : - Supplies 28VDC to the close coils of the BAR, - Supplies a ground to the BLEED TRIP OFF light and the master caution system (this makes the lights come on), - Makes a latch circuit for the overheat relay through the P5-10 panel TRIP RESET push-button switch. To get control of the engine bleed system after a bleed trip off, these conditions must occur : - The overpressure or overheat switch must go back to its normal (open) condition, - Push the P5-10 panel TRIP RESET push-button switch (to open the overheat relay latch circuit). page 60 10 - 12 - 2013 rev : 4
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BLEED TRIP OFF SCHEMATIC page 61 10 - 12 - 2013 rev : 4
Training manual
B737NG/36/301 Pneumatic System
8.3. Dual Bleed Light. The DUAL BLEED light does these things : - Tells the crew that an engine (or engines) and the APU both supply pressure to the pneumatic manifold at the same time, - Reminds the crew to put the thrust levers to the idle position during DUAL BLEED conditions, Functional Description. The DUAL BLEED indication circuit uses 28V DC electrical power. Power goes to the light when the bus has power. When airplane logic supplies a ground to the circuit, the light comes on. The circuit has two paths to ground. Both paths rely on switch and valve position logic. The DUAL BLEED light comes on for these conditions : - Engine 1 BLEED switch ON and the APU bleed air valve open, - Engine 2 BLEED switch ON, the isolation valve OPEN, and the APU bleed air valve open. The DUAL BLEED light can make sure that the APU bleed air valve is in the close position. When the APU bleed valve is open and the engine 1 BLEED switch is ON, the DUAL BLEED light shows the valve is not in the close positlon. When the APU BLEED switch is OFF and the engine 1 BLEED switch is ON, the DUAL BLEED light will go off when the APU bleed air valve closes.
page 62 10 - 12 - 2013 rev : 4
Training manual
B737NG/36/301 Pneumatic System
DUAL BLEED SCHEMATIC page 63 10 - 12 - 2013 rev : 4
Training manual
B737NG/36/301 Pneumatic System
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page 64 10 - 12 - 2013 rev : 4
Training manual
B737NG/36/301 Pneumatic System
ENGINE BLEED AIR ( L ENG SHOWN) page 65 10 - 12 - 2013 rev : 4
