AM AM Hydraulic & Pneumatic Systems 2 — Questions and Answers
Question 1: What is the purpose of a bootstrap reservoir in an aircraft hydraulic system?
- Store emergency fluid supply at low pressure
- Pressurize the reservoir using system hydraulic pressure (Correct answer)
- Filter return line fluid
- Separate air from hydraulic fluid
Correct 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.
Question 2: When bleeding a hydraulic system, why must air be completely removed?
- Air causes fluid to overheat only
- Air is compressible and causes spongy, unpredictable actuator response (Correct answer)
- Air accelerates seal wear only
- Air increases fluid viscosity
Correct 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.
Question 3: A hydraulic pump that delivers a fixed volume of fluid per revolution regardless of system pressure is called:
- Variable-displacement pump
- Fixed-displacement (constant delivery) pump (Correct answer)
- Demand pump
- Electric motor pump
Correct 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.
Question 4: What is the primary advantage of a variable-displacement hydraulic pump over a fixed-displacement pump?
- Lower initial cost
- Simpler internal design
- Reduces flow when pressure demand is met, saving power and reducing heat (Correct answer)
- Higher pressure output capability
Correct 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.
Question 5: Aircraft pneumatic systems typically use which gas as the working medium?
- Hydrogen
- Nitrogen or filtered, dried air (Correct answer)
- Oxygen
- Carbon dioxide
Correct 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.
Question 6: What component prevents back-flow in a hydraulic line when downstream pressure exceeds upstream pressure?
- Relief valve
- Check valve (Correct answer)
- Selector valve
- Flow restrictor
Correct 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.
AM AM Hydraulic & Pneumatic Systems 2
What is the purpose of a bootstrap reservoir in an aircraft hydraulic system?