Pneumatics Flashcards
What do large gas turbine a/c use for their pneumatic system
Engine bleed air
Small a/c have a pneumatic system driven by
A vacuum pump driven by the engine via a quill shaft
What is quill drive designed to do if the torque load becomes excessive
Designed to shear if the torque load becomes excessive
Some older turboprop and piston engined a/c use pneumatics for
L/d gear
Brakes
Flaps
Moisture separator
Prevents ice buildup which could come from moist air - takes the moisture out
Desiccator
Picks up any excess moisture after the moisture separator
When is the emerg system used - pneumatics blower system
When the isolation valve is closed
Adv and disadv of an air pressure system
Won’t run out
More dangerous - high pressure system - you can’t see if there is a leak
Cheaper, simpler and lighter
Blower
Sucks air in - compressor
Mass flow control valve - blower system
Controls the mass flow to maintain the correct amount in the cabin - will send a signal to the spill valve to open/close to maintain the correct mass of air
Choke valve purpose and how it works
Located in the cabin blower system - purpose - raise the temp of the air if required
How - applying a back pressure to the blower
Pack valve
Controls the air conditioning - either on/off
How does the a/c regulate the mass flow for an a/c using bleed air for pneumatics
Mass flow controller sends a signal to the variable metering orifice which opens and closes to maintain the correct mass flow
Bleed air is fed from
From the LP stages of the Hp compressor
From the engine compressor
Bleed air is cooled by
An air conditioning pack
Isolation valve
Allows each pneumatic system to work in isolation - once opened one engine can supply both engines
HPSOV
Designed to open slowly on eng start to prevent a surge of air pressure - also req to close quickly to stop smoke and fumes reaching the cabin
Materials for pneumatics
Plastic and fibre glass for low pressure systems
Stainless steel for high pressure systems
Normal cause of overpressure - pneumatics
Usually caused by the failure of the high pressure shut off valve - sensor drives the valve shut
Safety device to prevent overheat
Electrical temp switch downstream of the bleed air control valve will close the valve
Overheat action by the pilot - pneumatics
Close the bleed switch and then open the isolation valve to make up for the lost system - allows 1 engine to supply both a/c packs
Light a/c obtain hot air from and the possible risk
A heat exchanger wrapped around the exhaust this is then mixed with cold air - risk of carbon monoxide
Can also receive to air from a combustion heater
Combustion heater
Burns fuel to generate heat and warm the air
Separated heating to keep you warm
Takes heat from the fuel the tanks and burns it
Safety devices required with a combustion heater
Automatic fuel shutoff
Adequate fire protection
Purpose of air conditioning
To supply a constant delivery of clean air, to the cockpit and cabin, within a set temp range
What is conditioned air
Air which is treated for pressure and temp
Do we control humidity
No
We take all the water out and put a little back in
Fresh air requirements
1 pound of fresh air per seat per min under normal circumstances
0.5 pound of fresh air per seat per min following a failure of any part of the system - lowest is can be
Between 18 - 24*C
At 40,000ft the humidity is about
1-2%
Ideally it should be about 30%
Carbon monoxide contamination not to exceed
1 part in 20,000 - legal limit
Bootstrap (air cycle) system consists of
In the specific order of Primary heat exchanger (precooler) Compressor Secondary heat exchanger (intercooler) Turbine
It is the combined effect of the secondary heat exchanger and the turbine = cooling
Bootstrap system is most efficient at
High mass flow values
Cold air unit/air cycle machine in a bootstrap system is made up of
Compressor, shaft, turbine
When stationary/slow in the air - how does the a/c provide ram air
Uses a fan powered by an electric motor - electrically driven of by a third wheel on the cold air unit
2 types of water separators and where it is located
Impingement or centrifugal
Located downstream of the turbine/ air cooler
Centrifugal water separator
Air-driven fan throws water outwards - water is drained and collected
Impingement water separator
Moisture sticks to the cold collector tubes and collects at the bottom
How does the humidifier work
Same as a carburettor- air tube - sucks water out and into the airflow
What is the recirculating fans
Draws air from underfloor area through filters and is reintroduced into the conditioned distribution system - prevents stagnation
What is gasper air
Cold conditioned air supplied to the pax through punkah louvres
Trim air
Low pressure, high temp air
Allows us to control different temps in each cabin
