Airframe Mechanic Certification Hydraulic and Pneumatic Power 5 — Questions and Answers
Question 1: A shuttle valve in a hydraulic system is used to:
- Control flow direction with a rotary selector
- Automatically select the higher of two pressure sources to supply a critical component (Correct answer)
- Reduce system pressure to a lower working pressure
- Sample fluid for contamination testing without opening the system
Correct answer: Automatically select the higher of two pressure sources to supply a critical component
A shuttle valve connects a component to whichever of two supply sources (normal or emergency) has the higher pressure, ensuring continuous supply.
Question 2: What determines the maximum safe working pressure of a hydraulic hose assembly?
- The burst pressure divided by 10
- The manufacturer's published rated working pressure for that hose specification (Correct answer)
- The relief valve setting of the system where it is installed
- The wall thickness of the outer braid only
Correct answer: The manufacturer's published rated working pressure for that hose specification
Each hose assembly has a manufacturer-specified maximum working pressure that must equal or exceed the system's operating pressure.
Question 3: Fluid in an aircraft hydraulic reservoir is maintained above the minimum level primarily to:
- Keep the reservoir weight balanced
- Prevent pump cavitation and allow for thermal expansion of fluid (Correct answer)
- Maintain correct center of gravity
- Cool the hydraulic pump externally
Correct answer: Prevent pump cavitation and allow for thermal expansion of fluid
Adequate fluid level prevents the pump from drawing air (cavitation) and provides volume for fluid that expands when heated during operation.
Question 4: An aircraft pneumatic system using engine bleed air would MOST likely use bleed air from which compressor stage?
- The turbine exhaust stage for lowest pressure
- An intermediate or high-pressure compressor stage depending on engine power setting (Correct answer)
- The fan stage only
- The combustion chamber directly
Correct answer: An intermediate or high-pressure compressor stage depending on engine power setting
Bleed air is tapped from intermediate or high-pressure compressor stages, with automatic selection between stages to maintain adequate pressure across the flight envelope.
Question 5: What is the function of a priority valve in a hydraulic system?
- To sequence actuators in a specific order
- To ensure that flight-critical systems receive pressure before non-essential systems when pressure is low (Correct answer)
- To limit flow rate to prevent overheating
- To select between normal and alternate hydraulic sources
Correct answer: To ensure that flight-critical systems receive pressure before non-essential systems when pressure is low
A priority valve closes off non-critical hydraulic consumers when system pressure drops, reserving available pressure for flight-critical systems like flight controls.
Question 6: When installing a hydraulic fitting using the B-nut (flareless) tube fitting method, the sleeve is set by:
- Tightening the nut to a specified torque immediately at installation
- Pre-setting the sleeve onto the tube by tightening until resistance is felt, then backing off before final installation (Correct answer)
- Flaring the tube end with a flaring tool before assembly
- Applying thread sealant and torquing to the standard MS torque chart
Correct answer: Pre-setting the sleeve onto the tube by tightening until resistance is felt, then backing off before final installation
Flareless fittings require pre-setting the sleeve onto the tube in a presetting tool or union before final assembly to properly bite and grip the tube.
Question 7: If a hydraulic system pressure gauge reads zero with the pump operating, the FIRST item to check is:
- The relief valve setting
- Whether the system selector valve is open and the pump is actually receiving fluid (Correct answer)
- Fluid viscosity with a viscometer
- The accumulator precharge pressure
Correct answer: Whether the system selector valve is open and the pump is actually receiving fluid
Zero pressure with the pump running often indicates no fluid is reaching the pump (closed isolation valve, low reservoir) or the pump is not actually running, making fluid supply and pump operation the first checks.
Airframe Mechanic Certification Hydraulic and Pneumatic Power 5
A shuttle valve in a hydraulic system is used to: