Aeroplane Air-Mixing Valve
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Questions and Answers

What is the primary function of the air-mixing valve?

  • To separate water from the air
  • To control the flow of cold air to the pack
  • To regulate the temperature of the cabin
  • To control the proportion of hot and cold air to the pack and distribution system (correct)

    • How is the common disc shaft of the air-mixing valve driven?

  • By a manual control switch
  • By a temperature controller
  • By a 24-V DC motor
  • By a 115-V AC motor (correct)

    • What is indicated by the visual position indicator on the air-mixing valve?

  • The temperature of the pack
  • The speed of the motor
  • The pressure of the air
  • The position of the valve in the cold or hot range (correct)

    • What happens to the air when it goes through the cooling pack?

    <p>It gets cooled down</p> Signup and view all the answers

    What is the purpose of the water separator?

    <p>To condense water from air</p> Signup and view all the answers

    What controls the air-mixing valve?

    <p>The cabin temperature controller or the manual control switch</p> Signup and view all the answers

    What is the function of the position transmitter in the air-mixing valve?

    <p>To indicate the valve position</p> Signup and view all the answers

    What is the configuration of the air-mixing valve?

    <p>Two disc plates mounted on a common shaft 90° opposed</p> Signup and view all the answers

    What is the primary function of the temperature control valve?

    <p>To regulate the pack outlet temperature</p> Signup and view all the answers

    What happens when electrical power is applied to the temperature control valve?

    <p>The bleed port in the pressure chamber closes</p> Signup and view all the answers

    What is the purpose of the downstream temperature-sensing element?

    <p>To control the temperature control valve</p> Signup and view all the answers

    What happens to the valve in case of failure?

    <p>The valve moves to a spring-loaded closed position</p> Signup and view all the answers

    What is the function of the air mix valve in the air-cycle machine?

    <p>To bypass hot bleed air from the engines</p> Signup and view all the answers

    What is the result of repositioning the temperature control valve?

    <p>The pressure in the pressure chamber changes</p> Signup and view all the answers

    What is the type of control used in the temperature control valve?

    <p>Electrical and pneumatic control</p> Signup and view all the answers

    Where is the outlet air from the inlet typically routed to?

    <p>To the mix chamber</p> Signup and view all the answers

    What is the primary function of the Flow Control Shut-Off Valve in an air cycle system?

    <p>To control and adjust the flow of air into the air conditioning pack</p> Signup and view all the answers

    What is required to open the Flow Control Shut-Off Valve?

    <p>Both electrical power and upstream pneumatic pressure</p> Signup and view all the answers

    What happens when the dump valve solenoid is energized?

    <p>The valve opens to vent control pressure to ambient</p> Signup and view all the answers

    What is the failsafe position of the Flow Control Shut-Off Valve in the event of electrical power failure?

    <p>Fully open</p> Signup and view all the answers

    What happens to the secondary piston when the downstream pressure is too high?

    <p>It moves to open the bleed orifice</p> Signup and view all the answers

    What acts on the primary piston to open the Flow Control Shut-Off Valve?

    <p>Upstream pneumatic pressure</p> Signup and view all the answers

    What is the function of the lever mechanism in the Flow Control Shut-Off Valve?

    <p>To open the bleed orifice</p> Signup and view all the answers

    What is the location of the Flow Control Shut-Off Valve in an air cycle system?

    <p>In the air conditioning compartment</p> Signup and view all the answers

    What is the purpose of the overheat sensors in the supply duct?

    <p>To provide indication and stop operation when the temperature is out of limits</p> Signup and view all the answers

    What happens when the imbalance across the Wheatstone bridge is amplified?

    <p>The mixer valve varies temperature to rebalance the bridge</p> Signup and view all the answers

    What is the function of the duct temperature anticipator sensor?

    <p>To read the rate of change in the duct air temperature</p> Signup and view all the answers

    What happens when the temperature continues to climb despite the lower overheat sensor signaling the mixing valve to the full cold position?

    <p>The pack valve closes</p> Signup and view all the answers

    How does the resistance of the duct temperature anticipator sensor change as temperature increases?

    <p>It decreases</p> Signup and view all the answers

    What is the purpose of the actuator control in the temperature control system?

    <p>To move the mix-valve so that cabin temperature changes slowly and without raising duct temperature above limits</p> Signup and view all the answers

    What is the result of the system resetting after the temperature has cooled to below trip temperature?

    <p>The duct overheat warning light turns off</p> Signup and view all the answers

    Why are large aircraft often divided into zones for air distribution?

    <p>To provide more efficient temperature control</p> Signup and view all the answers

    What happens when the temperature of the cold bleed air in the water separator decreases towards freezing?

    <p>The low limit system adds hot bleed air to cold bleed air via the low limit valve</p> Signup and view all the answers

    What is the purpose of the temperature control valve in the air conditioning system?

    <p>To mix hot and cold air to regulate temperature throughout the cabin</p> Signup and view all the answers

    What signal is received by the temperature controllers from various sensors?

    <p>A signal to open or close the temperature control valves</p> Signup and view all the answers

    What is the function of the standby temperature control valve?

    <p>To provide backup control for the discharge temperature of the air conditioning pack</p> Signup and view all the answers

    What happens to the air in the mix chamber?

    <p>Hot air from the air mixing valve is added to cold air</p> Signup and view all the answers

    What is the purpose of the air-mixing valve in the air conditioning system?

    <p>To mix hot and cold air to regulate temperature throughout the cabin</p> Signup and view all the answers

    What is the primary function of the low limit system?

    <p>To prevent ice formation in the water separator</p> Signup and view all the answers

    What happens when the normal temperature control system fails?

    <p>The standby temperature control valve takes over</p> Signup and view all the answers

    What is the purpose of the gold coating on some pneumatic manifold ducts?

    <p>To reduce heat transfer</p> Signup and view all the answers

    What is the function of the isolation valve in the pneumatic manifold?

    <p>To divide the manifold into two separate systems</p> Signup and view all the answers

    What is the typical pressure range of air stored in metal bottles for high-pressure systems?

    <p>1000 to 3000 psi</p> Signup and view all the answers

    What is the purpose of the control valve in a high-pressure storage cylinder?

    <p>To act as a shutoff valve</p> Signup and view all the answers

    What is the purpose of overheat detectors in pneumatic ducts?

    <p>To detect high temperatures</p> Signup and view all the answers

    What is the advantage of using corrosion-resistant tubing for pneumatic manifold ducts?

    <p>It protects against corrosion</p> Signup and view all the answers

    What is the purpose of insulation blankets on some pneumatic ducts?

    <p>To decrease heat transfer</p> Signup and view all the answers

    What is a disadvantage of high-pressure storage cylinders?

    <p>They have a definite disadvantage</p> Signup and view all the answers

    What is the primary advantage of using compressed air over hydraulic or electrical systems?

    <p>It is universally available in an inexhaustible supply.</p> Signup and view all the answers

    In which range of pressure does a medium-pressure system operate?

    <p>50 to 150 psi</p> Signup and view all the answers

    What is the primary function of the venturi system in early light aircraft?

    <p>To provide a vacuum source.</p> Signup and view all the answers

    What is a potential problem that can be prevented by proper maintenance of filter systems?

    <p>Component failure and system contamination.</p> Signup and view all the answers

    What is one of the advantages of compressed air systems compared to hydraulic systems?

    <p>They are lighter.</p> Signup and view all the answers

    What is the range of pressure for high-pressure systems?

    <p>1000 to 3000 psi</p> Signup and view all the answers

    What is the primary limitation of using a pneumatic system for continuous operation of systems such as landing gear or brakes?

    <p>Insufficient air pressure</p> Signup and view all the answers

    What is the purpose of permanently installed air compressors on some aircraft?

    <p>To recharge air bottles whenever pressure is used</p> Signup and view all the answers

    What is the purpose of the filter in the venturi system?

    <p>To exclude dirt and moisture.</p> Signup and view all the answers

    What is the primary source of pneumatic power on the ground?

    <p>Mobile starter units</p> Signup and view all the answers

    What happens to the air in the venturi system as it accelerates through the narrowing section?

    <p>Its velocity increases.</p> Signup and view all the answers

    What is the typical location of low-stage bleed ports on a turbine engine?

    <p>Around stages five and ten</p> Signup and view all the answers

    What is the primary use of high-pressure bleed air?

    <p>During slow flight or descent</p> Signup and view all the answers

    What is the purpose of adding multiple air-pressurising units to an aircraft?

    <p>To increase system reliability</p> Signup and view all the answers

    What is the primary advantage of using an Airborne Auxiliary Power Unit (APU) as a pneumatic source?

    <p>Alternate source of air pressurization</p> Signup and view all the answers

    What is a limitation of using engine compressors as a pneumatic source?

    <p>Limited air supply during idle engine conditions</p> Signup and view all the answers

    What is the primary source of pneumatic air in some aircraft?

    <p>Bleed air taken from a gas turbine engine compressor</p> Signup and view all the answers

    What type of compressor is the Roots-type blower an example of?

    <p>Positive displacement compressor</p> Signup and view all the answers

    How is pressure controlled in a cabin system?

    <p>By using outflow valves</p> Signup and view all the answers

    What is the purpose of the check valves in a multi-stage compressor?

    <p>To allow air to flow in only one direction</p> Signup and view all the answers

    Why are independent cabin compressors designed to overcome the limitations of bleed air sources?

    <p>Because bleed air sources have many disadvantages</p> Signup and view all the answers

    What is the purpose of the fins on the Roots-type blower housing?

    <p>To provide some cooling and allow outside air to pass through</p> Signup and view all the answers

    What is the result of each rotation in a Roots-type blower?

    <p>Pressure increases</p> Signup and view all the answers

    What type of compressor can be driven by an accessory drive gearing or powered by bleed air from an engine compressor?

    <p>Independent cabin compressor</p> Signup and view all the answers

    What is the typical pressure range of a medium-pressure pneumatic system?

    <p>100-150 psi</p> Signup and view all the answers

    Where is the bleed air typically taken from in a turbine engine?

    <p>From the turbine engine compressor section</p> Signup and view all the answers

    What is the primary use of compressor bleed air in a turbine engine?

    <p>All of the above</p> Signup and view all the answers

    What is a limitation of high-pressure pneumatic systems?

    <p>They cannot be recharged in flight</p> Signup and view all the answers

    What is the purpose of the pressure-controlling unit in a medium-pressure pneumatic system?

    <p>To reduce the pressure of the bleed air</p> Signup and view all the answers

    What is the typical pressure range of air stored in metal bottles for high-pressure pneumatic systems?

    <p>1000-3000 psi</p> Signup and view all the answers

    What is the function of the control valve in a high-pressure pneumatic system air bottle?

    <p>To act as a shutoff valve</p> Signup and view all the answers

    What is the benefit of using bleed air from turbojet engines for medium-pressure pneumatic systems?

    <p>It is a readily available source of air</p> Signup and view all the answers

    Study Notes

    Air-Mixing Valve

    • Controls pack output temperature by directing airflow through the cooling pack or around the cooling pack to the mix chamber
    • Dual housing assembly with two disc plates mounted on a common shaft 90° opposed
    • Driven by a 115-V AC motor, controlled by the cabin temperature controller or manual control switch on the flight deck
    • Incorporates a visual position indicator showing the valve in the cold or hot range
    • Sends signals to the air-mixing valve position indicator on the cabin temperature control panel in the flight deck

    Temperature Control Valve

    • Used to control the pack outlet temperature
    • Electrically controlled and pneumatically operated
    • Relies on a signal from the downstream temperature-sensing element, controlled through the temperature control system
    • Fails safe closed in case of electrical power failure

    Air Cycle System Components

    • Flow Control Shut-Off Valve (FCSOV) controls and adjusts the flow of air into the air conditioning pack
    • Normally situated in the air conditioning compartment
    • Electrically controlled and pneumatically actuated
    • Regulates downstream pressure and flow

    FCSOV Valve Operation

    • Upstream bleed air pressure opens the valve
    • Downstream overpressure releases control pressure and modulates the valve to the closed position
    • Failsafe is in the open position in case of electrical power failure, maintaining air supply for pressurization

    Overheat Sensors

    • Located in the supply duct
    • Give indication and can stop operation when temperature is out of limits
    • Lower overheat sensor signals the mixing valve to the full cold position
    • Higher overheat sensor causes the pack valve to close

    Anticipator

    • Duct temperature anticipator sensor is part of a bridge circuit in the temperature controller
    • Reads the rate of change in the duct air temperature
    • Adjusts the air mix valve position to ensure cabin temperature changes slowly and without raising duct temperature above limits

    Separate Zone Control

    • Large aircraft may be divided into zones for air distribution
    • Low limit system adds partially cooled bleed air to cold bleed air to prevent ice in the water separator
    • Mix chamber adds hot bleed air from the hot side of the air mixing valve
    • Various cabin sensors give signals back to position the mixing valve, regulating temperature throughout the cabin

    Pneumatic Systems

    • In-flight pneumatic sources include engine compressors and an Airborne Auxiliary Power Unit (APU) as an alternate source.
    • Ground pneumatic sources include mobile starter units, ground pneumatic networks, APUs, and engine compressors.

    Engine Bleed Air Supply

    • Pressurized air is taken from the engine compressor in turbine engines (jet or turboprop).
    • Air is bled off the compressor at one or two places, usually around stages five and ten.
    • Low-pressure air (from the fifth stage) is used during take-off, climb, and cruise conditions.
    • High-pressure bleed air (from the tenth stage) is used during slow flight or descent, where engine power is reduced.

    Bleed Air Distribution

    • Pneumatic systems that use bleed air include engine start, air conditioning, pressurization, engine inlet cowl anti-ice, wing thermal anti-ice, water tank pressurization, and total air temperature probe aspiration.

    Ducts

    • Pneumatic manifold ducts are made of strong, corrosion-resistant, lightweight tubing.
    • Some ducts have a gold coating to protect against hydrocarbon contamination and decrease heat transfer.
    • Insulation blankets cover some ducts to reduce heat transfer.
    • Overheat detectors are located near the pneumatic ducts to detect leaking ducts.

    High-Pressure Distribution System

    • High-pressure systems store air in metal bottles at pressures ranging from 1000 to 3000 psi.
    • The bottles have a charging valve and a control valve (shutoff valve).
    • The system is limited by the small supply of bottled air, as it cannot be recharged in flight.

    Compressors

    • Independent cabin compressors are designed to overcome the disadvantages of bleed air sources.
    • Compressors can be driven by accessory drive gearing or powered by bleed air from an engine compressor.
    • Types of compressors include positive displacement compressors (Roots-type blower) and centrifugal compressors.
    • Positive displacement compressors work like a gear pump, taking a predetermined volume of air, compressing it, and delivering it to the cabin duct.

    Medium-Pressure Systems

    • Medium-pressure pneumatic systems (100–150 psi) do not include an air bottle.
    • Compressed air is taken from the turbine engine compressor section or a separate compressor device.
    • The bleed air is routed to a pressure-controlling unit to reduce the pressure to about 40 psi and then distributed to the operating units.

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    Description

    This quiz covers the air-mixing valve in aeroplane systems, including its function and installation. It is part of the CASA Part 66 training materials.

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