11.16 Pneumatic And Vacuum Flashcards
What is pneumatics
Using pressurised or compressed gas as a source of power
What gas is normally used in pneumatics
Air
What is pneumatics used for on aircraft
- Engine starting
- Cabin Pressurisation and air conditioning
- Wing anti icing
- Water reservoir pressurisation and hydraulic reservoir pressurisation on some aircraft
What components work pneumatically
Air driven pumps for hydraulics and air motors used for slat operation
In any pneumatic system what two things need to remain as constant to support the different consumers effectively
Air pressure and temperature
Where does the biggest source of air come from on an aircraft
The engine compressor provides enough air for combustion purposes and for the pneumatic system
What is the air called which comes from the engine compressors
Engine Bleed Air (EBA)
Other than the engines what is the other supplier of bleed air?
The APU
If the aircraft is on the ground how can the pneumatic system be powered or fed
By external air delivered via connectors (High pressure Ground Connectors)
What is used to maintain a constant level of pressure and regulate the engine bleed air supply at high engine speeds
A pressure regulator known as the bleed valve
What is done when the engine is on idle ( and more air pressure is required)
A second bleed valve is opened on the engine
What two compressor stages supply the bleed air system
HP(High pressure) and IP (Intermediate pressure)
When the HP stage is supplying the pneumatic system what is needed to protect the engine compressor against back flow?
A check valve
What is used to shut off APU bleed air supply
The APU bleed valve
What is used to prevent APU back flow
A check valve
What happens to the temperature of the air when thrust increases
Temperature increases
What cools the bleed air when thrust is high
A built in pre cooler consisting of Fan air from the front of the engine is ducted off to cool the air
What is used to modulate how much fan air goes past the pre cooler
A fan air valve
What is pneumatic air distributed through
Ducts
What are the ducts known as
- The pylon duct
- The left and right wing ducts
- The APU duct
- The crossover duct or cross bleed manifold
What is used in the cross bleed manifold to isolate left from right wing pneumatic duct
A cross bleed valve
How are the pneumatic ducts monitored for leaks
By a leak detection system
How is the pneumatic system controlled from the cockpit
Either manually by the pneumatic panel or automatically by the pneumatic controller
How many pneumatic controllers are there per engine
One per engine
How is pressure in the system regulated
By valves, the main one called the bleed valve (pressure regulating shut off valve)
What is the final predetermined value of the pneumatic system
Around 45 psi in most pneumatic systems
What type of valve is the bleed valve
A butterfly valve
What functions does the bleed valve serve
- The shut off function
- A pressure regulation function
- A check valve function
- An over temperature control function
- A reverse flow function on some aircraft
A pneumatic controller controls all of these functions
What does a pneumatically operated valve consist of
- A valve body
- A closure element
- An actuator assembly
How does the actuator open the bleed valve
Pressure is picked up from the airflow moving towards the pressure plate, this is bled in to the open side of the actuator where it builds up. When the air pressure has builds up enough it will overcome the spring and move the piston. As a result the plate moves
What does the pre cooler air out temperature must be
Between 160-200 degrees c
What is used to monitor the in and out temperature of the air in the pre cooler
A thermostat
What is the reverse flow for
It is used to flow in the direction of the engines to start them
What pressure is the over pressure valve usually closed
85psi
What is the purpose of the overpressure valve
In the event of a failure it can dump pressure if it builds up to high
Other than an over pressure valve what is another method of overpressure relief
A pressure switch
What must be done before bleed air is bled from the HP compressor
The HP valve must be open
What is the standard size for ground connectors to connect external air
3 inches ( 3 inch ground connectors)
Where is the manual override for the cross bleed system
It is built in to the cross bleed valve for safety reasons
What are leaks monitored by
Overheat detectors
What does a leak result in
An overheat
What display page are all pneumatic performance indication on
EICAS or ECAM
What must be done when the aircraft is being supplied with external air
Make sure there is at least one window or door open to prevent accidental aircraft pressurisation
When is the only time that the APU bleed valve is shown on ECAM
When the APU is running
