13.18 Pneumatic/Vacuum Flashcards
What are the advantages of pneumatic systems?
Lightweight
Safe
Reliable
Eco–friendly
Small (can be)
Unaffected by atmospheric changes
Inexpensive components
Pressure seals are usually problem free
Forces transmitted are easy to manage (within acceptable PSI limits)
What is caused by increasing the pressure of a volume of air, and what is therefore required in a compressor?
Increasing pressure causes an increase in temperature
Cooling fins on the compressor
How does a compressor increase the pressure of the air?
Volume of each successive stage is smaller than the preceding one
What stage of air is exhausted to atmosphere when the pressure regulator is open?
Third stage air
What encourages the air to spin in a oil and water trap?
Radial drillings
In a pneumatic system, what component is used to remove the last of the oil and water from the system?
Dehydrator
What is contained in the dehydrator which will remove oil and water from the air?
Dessicant – Activated alumina
What should be carried out if moisture is found in the air filter housing?
Oil and water trap should be examined for faults
What are commonly used as filters in the pneumatic system filters?
Paper gauze
Glass wool
Felt
Fine metal mesh
How are air storage cylinders usually mounted?
In the upright position
How is the operating pressure of a relief valve changed?
Adjustable by means of increasing or decreasing spring pressure
How does a pressure maintaining valve operate?
Allows pressure to primary/essential systems as well as secondary/non–essential systems
At a loss of pressure, shuts off pressure to secondary/non–essential
What might a pressure maintaining valve also be called?
Priority or pressure regulating valve
In a pneumatic actuator, how is damping achieved?
Forcing grease through an annular space between the inner wall of the piston rod and a stationary damper piston
What might air extracted from gas turbine engines also be known as?
Charge air
What might charge air be used for?
Cabin air conditioning and pressurisation
Anti–icing
Drinking water pressurisation
Hydraulic reservoir pressurisation
In an engine air bleed pneumatic system, what is the main supply of compressed air provided by?
Low pressure/intermediate stages of the engine compressor
In an engine air bleed pneumatic system, what happens under reduced power settings?
High stage valve will open to allow the high–pressure compressor to satisfy the demands of the user system
In an engine air bleed pneumatic system, what does the distribution system do?
Interconnects the engine bleeds and the bleed from the APU
Contains all the necessary valves to shut off bleed air at each engine and isolates various ducts
Where does some of the hot air from the low/intermediate stage compressor go?
Forward to the engine cowling anti–icing system if selected
When will a pressure relief valve open in the duct coming from the low/intermediate stage compressor?
If the duct pressure exceeds 100 lb/in²
In an engine air bleed pneumatic system, what are the four functions of the Pressure Regulator and Shut–off Valve?
Opens or closes in response to the control switch on the bleed air control panel in the crew compartment, or when temperature and pressure limits are exceeded (will also close when the engine fire handle is operated to arm the extinguisher circuit)
Prevents reverse flow when duct pressure exceeds engine supply pressure
Modulates to limit pressure in the pneumatic manifold to approximately 45 lb/in²
Limits temperature to 230 °C
In an engine air bleed pneumatic system, what is the pre–cooler also known as, and what temperature does it cool bleed air to?
200°C to 230 °C
In an engine air bleed pneumatic system, how does a pre–cooler cool the bleed air?
Uses cold air from the engine fan
In an engine air bleed pneumatic system, what happens to the fan air which is used to cool bleed air in the pre–cooler?
Discharged to atmosphere after passing through the cooler matrix
In an engine air bleed pneumatic system, how is the amount of cooling air from the fan controlled?
By the pre–cooler control valve
What delineates the air conditioning system from the bleed air system?
Pack valve
At what RPM will the APU bleed valve open to supply air to the pneumatic system?
95%
In an engine air bleed pneumatic system, what are the three positions of the isolation valve?
Close
Open
Auto
In an engine air bleed pneumatic system, what position is the isolation valve in when ‘auto’ is selected and all engine bleed air and air conditioning packs are operating?
Closed
Under what conditions will the APU bleed valve close automatically, even if the APU is running at 95% or above RPM?
APU fire–warning switch is operated to arm the fire extinguisher
What must all external supplies, whether from high pressure storage cylinders or mobile compressors, be fitted with to ensure that the air is clean and dry?
Oil and water traps
Preferably a dyhydrator
How are you to check for leaks of a pneumatic system?
Not using hands
Strips of cloth placed on a rod
or
Special leak detection liquids
What are the three conditions which usually apply to duct maintenance and repair?
Smooth dents are normally permissible providing they do not restrict the flow of air through the duct
Shallow scratches and gouges are permissible if they are not more than 10% of duct wall thickness, and providing the bottom of the scratch is smooth
Any defect or damage within approximately 1/4 (6mm) of a weld renders the duct unserviceable and it should be replaced”
What is the system identification label for:
Fuel
Pneumatic
Lubrication
Hydraulic
Fuel – four pointed star
Pneumatic – no–matic
Lubrication – black square
Hydraulic – black circle
What is the maximum pressure supplied through the pneumatic ground service connection?
40 – 45 lb/in²
How does a pneumatic ground service connection prevent loss of air through the connection during normal operation of the aeroplane bleed air system?
One way valve
What is the pressure in the potable water system provided by engine bleed air?
10 – 15 lb/in²
In an engine air bleed pneumatic system, how does the pre–cooler control valve work?
Oil filled sensing element which operates a push rod
When normal temperature is reached, the oil expands and a ball is unseated by the push rod
Valve opens, increasing the flow of cooling air from the fan
What are the two basic types of air pumps?
Wet and dry
What component vents third stage air pressure to atmosphere in a pneumatic system?
Pressure regulator
What is the main disadvantage of pneumatic power generation?
Loud
Compressible fluid
Difficult to control position
In order, what are the components in a typical high pressure system up to the service selector valve?
Compressor (pumps)
Oil and water trap
Dehydrator
Air filter
Air storage cylinder
Pressure relief valve
Pressure reducing valve
Pressure maintaining valve
Isolation valve
What happens when duct temperature reaches 230°C?
Atmospheric port is opened
Reducing control air pressure at the bleed air regulator
Regulator and shut–off valve move towards the closed position
Reduces the amount of bleed air passing through the pre–cooler
Less hot bleed air flowing, the pre–cooler will cool it more efficiently
What will happen when the bleed air over temp switch operates?
At 255°C
Warning light on the bleed air control panel will illuminate
Closes the pressure regulator and shut–off valve
What is the purpose of the check valve?
Prevents reverse flow from the high pressure stage
What happens when duct pressure exceeds 100 psi?
Pressure relief valve will open
APU air is selected but no air services are operating, state the potential cause?
APU is running below 95 rpm
