Aircraft pneumatic component repair
Aircraft pneumatic systems
Aircraft pneumatic systems work in a very similar way to hydraulic systems. The
difference is that in pneumatic systems high-pressure air is used instead of hydraulic fluid. Like
hydraulics, pneumatic pressure can be stored in an accumulator. This can give a reserve of power for short
bursts of very heavy operation, or for emergency use if the system fails. Using air as a medium for
transmitting motion has another advantage - no return line is needed. The exhausted air is vented directly to
atmosphere, although the venting of large volumes of air under pressure must be allowed for in the design of
nearby structure.
Aircraft pneumatic component overhaul can be undertaken as readily as aircraft
hydraulic component repair. However, the compressibility of air can be a major disadvantage. Aircraft
pneumatic systems lack the instant response that hydraulic systems provide, and the rate of movement of
pneumatic actuators is highly load-dependent. This compressibility also means that the position of systems
needing partial movements, such as control surfaces, cannot easily be controlled with any degree of accuracy,
since even when the flow has stopped the actuator will move in response to load variations.
Another disadvantage of pneumatic systems is their inefficiency in transmitting power,
because energy is lost in compressing the air. This does not occur with hydraulic fluids.
Pneumatic ducting connectors
Another feature of aircraft pneumatic component repair is that pneumatic ducting
systems and connectors have to be manufactured to close tolerances to be airtight. Peri-seal connectors are
still designed into aircraft today, although invented fully 50 years ago. Because of these major
disadvantages, many aircraft are not fitted with pneumatic systems. However, many aircraft use compressor
bleed air to do certain tasks. Because gas-turbine engines generate hot air at relatively high pressure, a
small amount of this air can be used in anti-icing systems. Bleed air is used on many aircraft to supply the
power and heat to operate cabin pressurisation and air conditioning systems. This air is not passed directly
into the cabin, but through a cold-air unit, where it is cooled and then mixed with the correct amount of hot
air to provide the optimum temperature for the comfort of passengers and crew.
The humidity is also important, and this is controlled by adding the required amount
of water, as determined by devices called humidistats.
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