1. AIRCRAFT PNEUMATIC SYSTEMS

2. It employs air instead of a liquid for transmitting power.
Pneumatic systems are sometimes used for:
• Brakes
• Opening and closing doors
• Driving hydraulic pumps, alternators, starters, water injection pumps, etc.
• Operating emergency devices

3. Both pneumatic and hydraulic systems are similar units and use confined fluids.
Liquids are practically incompressible; a quart of water still occupies about a quart of space regardless of how hard it is compressed.
Gases are highly compressible
Pneumatic System Components
do not utilize reservoirs, hand pumps, accumulators, regulators, or engine-driven or electrically driven power pumps for building normal pressure.
But similarities do exist in some components.

5. Air Compressors
On some aircraft, permanently installed air compressors have been added to recharge air bottles whenever pressure is used for operating a unit.
Relief Valves
Relief valves are used in pneumatic systems to prevent damage. They act as pressure limiting units and prevent excessive pressures from bursting lines and blowing out seals.
Control Valves
Control valves are also a necessary part of a typical pneumatic system.
Check Valves
Check valves are used in both hydraulic and pneumatic systems.

6. Restrictors
Restrictors are a type of control valve used in pneumatic systems. The small outlet port reduces the rate of airflow and the speed of operation of an actuating unit.
Filters
Pneumatic systems are protected against dirt by means of various types of filters.
1. Micronic filter
2. Screen-type filter

7. Desiccant/Moisture Separator
The moisture separator in a pneumatic system is always located downstream of the compressor. Its purpose is to remove any moisture caused by the compressor.
A complete moisture separator consists of a reservoir, a pressure switch, a dump valve, and a check valve.
Chemical Drier
Chemical driers are incorporated at various locations in a pneumatic system. Their purpose is to absorb any moisture that may collect in the lines and other parts of the system. Each drier contains a cartridge that should be blue in color.

8. Types of Typical air pressure system
High pressure system
Medium pressure system
Low pressure system

9. High pressure system
For high pressure systems air is usually stored in metal bottles
Pressure ranging from 1000 to 3000psi
Has two valves
Charging valve and
Ground operated compressor

10. Medium pressure system
Pressure ranging from 100 to 150psi
Does not include air bottles
Draws air from jet engine compressor section
Low pressure system
Pressure ranging less than 100 psi
Used in reciprocating types of aircraft
Driven by electric motors or by aircraft engine