Airframe Mechanic Hydraulic and Pneumatic Power Questions and Answers — Questions and Answers
Question 1: In a typical aircraft hydraulic system, what is the primary function of a hydraulic accumulator?
- To filter contaminants from the hydraulic fluid.
- To store hydraulic fluid under pressure for normal and emergency use. (Correct answer)
- To regulate the system pressure by bypassing excess fluid back to the reservoir.
- To cool the hydraulic fluid by routing it through a heat exchanger.
Correct answer: To store hydraulic fluid under pressure for normal and emergency use.
A hydraulic accumulator is a steel sphere or cylinder containing a diaphragm or piston that separates hydraulic fluid and compressed nitrogen. Its main purposes are to store fluid under pressure to supplement the pump during peak demand, dampen pressure surges, and provide a source of hydraulic power for limited emergency operations if the pump fails.
Question 2: A maintenance technician is servicing an aircraft that uses a phosphate ester-based hydraulic fluid (e.g., Skydrol). Which of the following is a critical precaution when handling this type of fluid?
- It is highly flammable and requires special fire prevention procedures.
- It is compatible with natural rubber seals and hoses.
- It is extremely susceptible to contamination from water in the atmosphere. (Correct answer)
- It can be mixed with mineral-based hydraulic fluids like MIL-H-5606.
Correct answer: It is extremely susceptible to contamination from water in the atmosphere.
Phosphate ester-based hydraulic fluids, like Skydrol, are known for their fire resistance but are very hygroscopic, meaning they readily absorb moisture from the air. Water contamination can lead to fluid breakdown and corrosion within the hydraulic system. They are also not compatible with many materials used with mineral-based fluids, and mixing fluid types can cause severe system damage.
Question 3: What is the key difference between a hydraulic system pressure relief valve and a pressure regulator?
- A relief valve regulates normal system pressure, while a regulator is for emergency overpressure events.
- A relief valve is a safety device to prevent over-pressurization, while a regulator maintains a specific downstream pressure. (Correct answer)
- A regulator is installed in the return line to the reservoir, while a relief valve is in the pressure line.
- A relief valve is manually operated, whereas a pressure regulator is fully automatic.
Correct answer: A relief valve is a safety device to prevent over-pressurization, while a regulator maintains a specific downstream pressure.
A pressure relief valve is primarily a safety device that opens only when system pressure exceeds a preset limit, venting excess pressure to prevent damage. A pressure regulator is designed to continuously maintain a specific, controlled pressure in a portion of the system that is lower than the main system pressure.
Question 4: An aircraft's pneumatic system, often powered by engine bleed air, is commonly used to operate which of the following systems?
- Primary flight controls like ailerons and elevators.
- Windshield wipers and cargo doors.
- Cabin pressurization, air conditioning, and anti-icing systems. (Correct answer)
- Hydraulic pumps and fuel boost pumps.
Correct answer: Cabin pressurization, air conditioning, and anti-icing systems.
Engine bleed air is a primary source for aircraft pneumatic systems. This high-temperature, high-pressure air is ideal for operating systems like cabin air conditioning packs, cabin pressurization outflow valves, and wing and engine anti-ice systems.
Question 5: While troubleshooting a hydraulic system for sluggish operation, the mechanic finds the fluid has a milky appearance. What is the most likely cause of this condition?
- The system is operating at too high a temperature.
- The wrong viscosity of hydraulic fluid was added.
- The hydraulic fluid is contaminated with air or water. (Correct answer)
- The system's micronic filters are clogged and need replacement.
Correct answer: The hydraulic fluid is contaminated with air or water.
A milky or foamy appearance in hydraulic fluid is a classic sign of contamination with either air or water. Air can be introduced through leaks in the suction side of the pump, while water can enter through contaminated servicing equipment or condensation. Both contaminants degrade system performance and can cause corrosion and damage to components.
Question 6: Which component in a pneumatic system is used to allow airflow in one direction but prevent it from flowing in the opposite direction?
- Shuttle valve
- Orifice
- Relief valve
- Check valve (Correct answer)
Correct answer: Check valve
A check valve is a one-way valve that permits compressed air (or hydraulic fluid) to flow in one direction only. It uses a spring-loaded ball or poppet that unseats to allow forward flow but is forced against its seat to block any reverse flow.
Airframe Mechanic Hydraulic and Pneumatic Power Questions and Answers
In a typical aircraft hydraulic system, what is the primary function of a hydraulic accumulator?