FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
During a walkaround, a technician notices the reservoir on a hydraulic system has a small sight gauge and is connected to a bleed-air line from the pneumatic system. What is the primary purpose of pressurizing the hydraulic reservoir with bleed air?
- ATo ensure a positive flow of fluid to the pump inlet and prevent cavitation
- BTo increase the viscosity of the hydraulic fluid
- CTo cool the hydraulic fluid before it enters the pump
- DTo allow the reservoir to double as an accumulator for emergency extension
Show answer & explanationAnswer & explanation
Correct answer: A. To ensure a positive flow of fluid to the pump inlet and prevent cavitation
Pressurizing the reservoir forces fluid to the pump inlet, especially at altitude where low ambient pressure could otherwise allow the fluid to boil or the pump to cavitate. This is not related to viscosity, cooling, or accumulator function.
Why the other options are wrong
- B. Bleed air pressure has no effect on fluid viscosity.
- C. Reservoirs are not designed as heat exchangers via bleed air.
- D. Accumulator function requires a separate component with a gas/fluid piston or diaphragm.
Pressurized Reservoir
A hydraulic reservoir supplied with bleed air or system pressure to maintain positive pressure at the pump inlet.
- Prevents pump cavitation at altitude
- Uses bleed air or system pressure
- Common on transport category aircraft
Memory trick: Push fluid to the pump so it never runs dry — pressurize!