A technician is comparing two hydraulic reservoir pressurization designs used to ensure a positive fluid supply to the engine-driven pump inlet. One design uses regulated engine bleed air ducted directly into the reservoir air space above the fluid. The other uses a small internal piston, actuated by system return pressure, to pressurize the fluid. The first design (using regulated bleed air directly) is known as a(n):
- AVented (unpressurized) reservoir
- BAir-pressurized reservoir
- CAccumulator-pressurized reservoir
- DBootstrap reservoir
Show answer & explanationAnswer & explanation
Correct answer: B. Air-pressurized reservoir
An air-pressurized reservoir uses regulated air (such as engine bleed air or an external air source) ducted directly into the air space above the fluid to maintain positive pressure at the pump inlet, which helps prevent pump cavitation at altitude. This differs from a bootstrap reservoir, which uses a piston actuated by hydraulic system pressure (rather than direct air) to accomplish the same pressurizing function without requiring an external air source.
Why the other options are wrong
- A. A vented reservoir is open to ambient atmospheric pressure and provides no positive pressurization at altitude.
- C. Accumulator-pressurized is not a standard reservoir classification; accumulators are separate components.
- D. A bootstrap reservoir uses a hydraulically actuated piston rather than direct air pressurization.
Air-Pressurized Reservoir
A hydraulic reservoir design that uses regulated air (e.g., engine bleed air) ducted directly into the reservoir's air space above the fluid to maintain positive pressure at the pump inlet.
- Prevents pump cavitation, especially at altitude
- Contrasts with bootstrap reservoirs, which use a hydraulic piston instead of direct air
- Requires a regulated air source and pressure regulating valve
Memory trick: Air-pressurized: air blows straight into the tank; bootstrap: fluid pressure pulls its own bootstraps