Airframe Mechanic Certification Hydraulic and Pneumatic Power 4 — Questions and Answers
Question 1: What type of actuator converts hydraulic pressure into linear mechanical motion?
- Rotary actuator
- Linear actuator (hydraulic cylinder) (Correct answer)
- Hydraulic motor
- Torque converter
Correct answer: Linear actuator (hydraulic cylinder)
A linear actuator (hydraulic cylinder) uses fluid pressure acting on a piston to produce straight-line mechanical force and movement.
Question 2: Which component prevents reverse flow in a hydraulic or pneumatic line?
- Shuttle valve
- Check valve (Correct answer)
- Selector valve
- Priority valve
Correct answer: Check valve
A check valve allows flow in only one direction and blocks reverse flow, protecting upstream components from back-pressure.
Question 3: The purpose of a hydraulic snubber on a pressure gauge is to:
- Amplify pressure readings for accuracy
- Dampen pressure surges to protect the gauge and provide steady readings (Correct answer)
- Convert hydraulic pressure to pneumatic for the gauge
- Filter particulates before they reach the gauge internals
Correct answer: Dampen pressure surges to protect the gauge and provide steady readings
A snubber is a restrictor that dampens rapid pressure fluctuations, protecting the gauge mechanism from damage and providing a stable, readable indication.
Question 4: When MIL-PRF-5606 (red) and MIL-PRF-83282 (red) hydraulic fluids are inadvertently mixed, the result is:
- A fire hazard due to chemical reaction
- Generally acceptable because both are petroleum-based and compatible (Correct answer)
- A corrosive mixture that damages seals immediately
- Complete system failure due to viscosity incompatibility
Correct answer: Generally acceptable because both are petroleum-based and compatible
MIL-PRF-5606 and MIL-PRF-83282 are both petroleum-based mineral oils and are considered compatible with each other and the same seal materials.
Question 5: A double-acting hydraulic actuator differs from a single-acting actuator in that it:
- Uses two hydraulic pumps simultaneously
- Can apply hydraulic pressure to extend AND retract the piston (Correct answer)
- Contains two pistons in one cylinder body
- Operates on both hydraulic and pneumatic pressure
Correct answer: Can apply hydraulic pressure to extend AND retract the piston
A double-acting actuator has ports on both sides of the piston, allowing hydraulic pressure to power both extension and retraction strokes.
Question 6: Hydraulic system contamination is MOST commonly introduced during:
- Normal pump operation
- Maintenance when lines are opened and fluid is serviced (Correct answer)
- System pressurization on the ground
- High-altitude cruise flight
Correct answer: Maintenance when lines are opened and fluid is serviced
Most contamination enters hydraulic systems during maintenance activities when lines are disconnected, components are replaced, or fluid is added.
Question 7: What is the primary advantage of a variable-displacement hydraulic pump over a fixed-displacement pump?
- Lower initial cost and simpler construction
- Automatically adjusts output flow to match system demand, reducing heat generation (Correct answer)
- Higher maximum pressure output
- Elimination of the need for a hydraulic reservoir
Correct answer: Automatically adjusts output flow to match system demand, reducing heat generation
A variable-displacement pump reduces its output as system demand drops, minimizing heat buildup and energy waste compared to a fixed-displacement pump that must bypass excess flow through a relief valve.
Airframe Mechanic Certification Hydraulic and Pneumatic Power 4
What type of actuator converts hydraulic pressure into linear mechanical motion?