Airframe Mechanic Certification Hydraulic and Pneumatic Power 2 — Questions and Answers
Question 1: What is the primary purpose of a hydraulic accumulator in an aircraft system?
- To filter hydraulic fluid
- To store pressurized fluid for emergency use and dampen pressure surges (Correct answer)
- To regulate fluid temperature
- To convert hydraulic pressure to electrical power
Correct answer: To store pressurized fluid for emergency use and dampen pressure surges
Hydraulic accumulators store pressurized fluid to supplement pump output during peak demands and provide emergency pressure if the pump fails.
Question 2: Which type of hydraulic seal is used between two parts that have relative motion?
- Static seal
- Dynamic seal (Correct answer)
- Crush seal
- Flareless seal
Correct answer: Dynamic seal
Dynamic seals are designed to seal between moving parts, such as a piston moving within a cylinder.
Question 3: A pneumatic system loses pressure rapidly when the aircraft is on the ground. The MOST likely cause is:
- A faulty pressure gauge
- A leaking check valve or system component (Correct answer)
- Excessive compressor output
- High ambient temperature
Correct answer: A leaking check valve or system component
Rapid pressure loss indicates a leak in the system, most commonly at a valve, fitting, or line connection.
Question 4: What color coding identifies MIL-PRF-5606 hydraulic fluid?
- Blue
- Purple
- Red (Correct answer)
- Green
Correct answer: Red
MIL-PRF-5606 is a mineral-based hydraulic fluid identified by its red color.
Question 5: A relief valve in a hydraulic system is set to open at 3,000 PSI. The system normal operating pressure is 3,000 PSI. This setting is:
- Correct — the relief valve must open at system pressure
- Incorrect — the relief valve should be set 10% above normal operating pressure
- Incorrect — the relief valve protects against overpressure and must be set above normal operating pressure (Correct answer)
- Correct only if a bypass valve is installed
Correct answer: Incorrect — the relief valve protects against overpressure and must be set above normal operating pressure
A relief valve must be set above normal operating pressure so it only opens during overpressure conditions, not during normal operation.
Question 6: In a pneumatic system, a desiccant is used to:
- Increase air pressure
- Remove moisture from compressed air (Correct answer)
- Filter particulate matter
- Regulate airflow rate
Correct answer: Remove moisture from compressed air
Desiccants absorb moisture from compressed air to prevent corrosion and ice formation within pneumatic components.
Question 7: Which hydraulic pump type delivers a constant volume of fluid per revolution regardless of pressure?
- Variable-displacement piston pump
- Fixed-displacement gear pump (Correct answer)
- Variable-displacement vane pump
- Demand-controlled piston pump
Correct answer: Fixed-displacement gear pump
Fixed-displacement pumps like gear pumps deliver the same volume per revolution regardless of system pressure, relying on a relief valve to limit maximum pressure.
