FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
An engine-driven hydraulic pump on a transport category aircraft requires a positive fluid supply at its inlet during high-altitude, low-pressure conditions to prevent cavitation. Which reservoir design uses system fluid pressure acting on an internal piston to keep the reservoir fluid pressurized?
- AVented, non-pressurized reservoir
- BAir-pressurized reservoir using engine bleed air
- CBootstrap reservoir
- DAccumulator-assisted gravity feed reservoir
Show answer & explanationAnswer & explanation
Correct answer: C. Bootstrap reservoir
A bootstrap reservoir contains a floating piston; system pressure (often pump discharge pressure through an internal passage) acts on one side of the piston to pressurize the fluid on the other side. This self-pressurizes the reservoir without requiring an external bleed air source, ensuring positive pump inlet pressure at altitude.
Why the other options are wrong
- A. Vented reservoirs rely on atmospheric pressure only and are unsuitable at high altitude.
- B. Bleed-air pressurization uses external engine air, not internal system pressure on a piston.
- D. Accumulators dampen surges but don't describe this piston-pressurized reservoir design.
Bootstrap Reservoir
A hydraulic reservoir pressurized internally by a floating piston acted on by system hydraulic pressure, ensuring adequate pump inlet pressure at altitude.
- Uses internal piston, not external air
- Self-pressurizing from system pressure
- Prevents pump cavitation at altitude
Memory trick: Bootstrap 'pulls itself up' using its own system pressure.