ACS Hydraulic & Pneumatic Systems 3 — Questions and Answers
Question 1: What is the purpose of a pneumatic system bootstrap reservoir?
- Pressurize the reservoir above atmospheric pressure to prevent pump cavitation at altitude (Correct answer)
- Store excess bleed air for use during engine failure
- Cool pneumatic fluid before it enters actuators
- Act as an expansion chamber for thermal growth of pneumatic tubing
Correct answer: Pressurize the reservoir above atmospheric pressure to prevent pump cavitation at altitude
A bootstrap reservoir is pressurized above the fluid inlet pressure so the hydraulic or pneumatic pump receives adequate inlet pressure, preventing cavitation at high altitudes.
Question 2: Which component in a pneumatic system performs the same function as a hydraulic system relief valve?
- Pressure regulator
- Check valve
- Filter/separator
- Pressure relief valve (Correct answer)
Correct answer: Pressure relief valve
A pneumatic pressure relief valve protects the system from overpressure just as a hydraulic relief valve does, opening to vent excess pressure to atmosphere.
Question 3: What is the main hazard of moisture contamination in a high-pressure pneumatic system?
- Moisture increases fluid viscosity, reducing flow rates
- Moisture can freeze at altitude, blocking orifices and valves (Correct answer)
- Moisture causes pump cavitation at sea level
- Moisture reacts with nitrogen to form corrosive compounds
Correct answer: Moisture can freeze at altitude, blocking orifices and valves
Water moisture in pneumatic lines can freeze at altitude temperatures, blocking critical orifices, valves, and lines, causing system failure.
Question 4: When inspecting a hydraulic actuator for internal leakage, what is the most reliable method?
- Pressurize the extend port and check for fluid weeping at the retract port with both ports open
- Measure the time it takes the actuator rod to drift under a known load with ports blocked (Correct answer)
- Visually inspect the cylinder bore for scoring using a borescope
- Check the fluid level drop in the reservoir over a 24-hour period
Correct answer: Measure the time it takes the actuator rod to drift under a known load with ports blocked
Applying a load and timing rod drift with ports blocked reveals internal seal bypass, which is the definitive test for internal actuator leakage.
Question 5: What is the correct torque technique when installing AN/MS flareless tube fittings?
- Torque to the manufacturer's value using only a calibrated torque wrench
- Use the 'finger-tight plus turns' method specified in the applicable maintenance manual (Correct answer)
- Thread until metal-to-metal contact, then add 1/4 turn
- Tighten until resistance is felt, then tighten 1/16 turn more
Correct answer: Use the 'finger-tight plus turns' method specified in the applicable maintenance manual
Flareless fitting installation requires presetting the ferrule on the tube first, then during final assembly using the turns method specified in the maintenance manual.
Question 6: What is the purpose of a desiccant in an aircraft pneumatic system?
- Lubricate moving components within the pneumatic valves
- Remove moisture from compressed air before it enters system components (Correct answer)
- Filter particulate contamination larger than 10 microns
- Regulate downstream pressure to a constant value
Correct answer: Remove moisture from compressed air before it enters system components
A desiccant absorbs moisture from compressed air, preventing ice formation at altitude and corrosion within system components.
Question 7: What does a hydraulic system ground test unit (GTU) allow a technician to do?
- Test hydraulic systems with engines running at high power settings safely on the ground
- Operate aircraft hydraulic systems using external ground power without running the engines (Correct answer)
- Measure hydraulic fluid contamination levels during system operation
- Pressurize only the brake system independently from the main hydraulic system
Correct answer: Operate aircraft hydraulic systems using external ground power without running the engines
A ground test unit provides external hydraulic pressure and flow, allowing full system operation and testing without starting the aircraft engines.
ACS Hydraulic & Pneumatic Systems 3
What is the purpose of a pneumatic system bootstrap reservoir?