AM Hydraulic & Pneumatic Systems Flashcards

What is the purpose of a bootstrap reservoir in an aircraft hydraulic system?

Answer: Pressurize the reservoir using system hydraulic pressure

A bootstrap reservoir uses system hydraulic pressure applied to a piston to pressurize the reservoir, ensuring positive pump inlet pressure at altitude where atmospheric pressure is low.

When bleeding a hydraulic system, why must air be completely removed?

Answer: Air is compressible and causes spongy, unpredictable actuator response

Air is compressible unlike hydraulic fluid, so trapped air causes spongy, inconsistent actuator movement and can lead to unsafe control responses.

A hydraulic pump that delivers a fixed volume of fluid per revolution regardless of system pressure is called:

Answer: Fixed-displacement (constant delivery) pump

A fixed-displacement pump delivers the same volume per revolution regardless of system pressure; excess flow must be relieved or unloaded.

What is the primary advantage of a variable-displacement hydraulic pump over a fixed-displacement pump?

Answer: Reduces flow when pressure demand is met, saving power and reducing heat

Variable-displacement pumps reduce or eliminate output when system pressure is satisfied, saving engine power and reducing heat generation in the hydraulic fluid.

Aircraft pneumatic systems typically use which gas as the working medium?

Answer: Nitrogen or filtered, dried air

Aircraft pneumatic systems use dry nitrogen or filtered, moisture-free air to prevent corrosion and ice formation in valves and actuators.

What component prevents back-flow in a hydraulic line when downstream pressure exceeds upstream pressure?

Answer: Check valve

A check valve allows fluid flow in only one direction and closes automatically when downstream pressure exceeds upstream pressure, preventing back-flow.