FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
A pneumatic system compressor supplies air used to actuate landing gear doors on a light aircraft. Downstream of the compressor, a technician finds a canister filled with blue crystalline granules that turn pink when saturated. What is the function of this component?
- ATo absorb moisture from the compressed air and prevent icing/corrosion in the lines
- BTo reduce the oxygen content of the compressed air for fire safety
- CTo filter out metallic wear particles from the compressor cylinder walls
- DTo cool the compressed air before it enters the storage bottle
Show answer & explanationAnswer & explanation
Correct answer: A. To absorb moisture from the compressed air and prevent icing/corrosion in the lines
The canister contains silica gel desiccant, which absorbs moisture from compressed air produced by the compressor. Removing moisture prevents ice formation in pneumatic lines at altitude and reduces internal corrosion; the crystals change from blue to pink as they become saturated, signaling the need for replacement or drying.
Why the other options are wrong
- B. Desiccant does not alter oxygen content; that is unrelated to its function.
- C. Metallic particle filtration is performed by a separate mechanical filter, not desiccant.
- D. Cooling is performed by heat exchangers or radiators, not a desiccant canister.
Pneumatic System Moisture Separator/Desiccant
A canister of silica gel crystals placed downstream of a pneumatic air compressor to absorb moisture from compressed air, preventing icing and corrosion.
- Silica gel turns from blue to pink when saturated
- Prevents ice formation in pneumatic lines at altitude
- Located downstream of compressor, upstream of storage bottle
Memory trick: Blue crystal blush turns pink when it's had its fill of water