Airframe Mechanic Hydraulic and Pneumatic Systems Questions and Answers — Questions and Answers
Question 1: An aircraft's hydraulic system includes a component that stores fluid under pressure to dampen pressure surges, supplement the system pump during peak demand, and provide an emergency source of hydraulic power. What is this component called?
- A pressure regulator
- A sequence valve
- An accumulator (Correct answer)
- A shuttle valve
Correct answer: An accumulator
An accumulator is a steel sphere or cylinder divided into two chambers, one for hydraulic fluid and the other for compressed air or nitrogen. Its primary functions are to store hydraulic fluid under pressure, dampen pressure fluctuations, assist the pump during high demand, and provide emergency hydraulic power.
Question 2: During a landing gear extension sequence, the landing gear doors must open fully before the gear begins to extend. Which type of valve is specifically designed to control the sequence of operations between two different branches of a hydraulic circuit?
- Check valve
- Relief valve
- Selector valve
- Sequence valve (Correct answer)
Correct answer: Sequence valve
A sequence valve is designed to control the order of operations in a hydraulic system. It ensures that one action, like opening the gear doors, is completed before another action, like extending the landing gear, begins.
Question 3: A technician is servicing an aircraft's high-pressure pneumatic system, which is commonly used for emergency landing gear or brake operation. Which gas is typically used to service these systems due to its inert, non-flammable, and dry properties?
- Compressed air
- Oxygen
- Nitrogen (Correct answer)
- Carbon dioxide
Correct answer: Nitrogen
Nitrogen is the standard gas used for servicing high-pressure pneumatic systems, as well as charging struts and tires on aircraft. Its key advantages are that it is inert (non-reactive), non-flammable, and has a very low moisture content, which prevents internal corrosion and freezing at high altitudes.
Question 4: Pascal's Law is a fundamental principle governing hydraulic systems. Which of the following statements best describes this law?
- Fluid pressure is directly proportional to the fluid's velocity.
- Pressure applied to a confined fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel. (Correct answer)
- The force exerted by a fluid is equal to its mass times its acceleration.
- For every action in a fluid system, there is an equal and opposite reaction.
Correct answer: Pressure applied to a confined fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.
Pascal's Law states that when pressure is applied to a confined, incompressible fluid, the pressure is transmitted equally in all directions throughout the fluid. This principle allows hydraulic systems to multiply force.
Question 5: A maintenance technician is handling Skydrol, a common aviation hydraulic fluid. Which of the following is a critical characteristic of this fluid that necessitates careful handling and the use of personal protective equipment (PPE)?
- It is highly flammable at room temperature.
- It is a petroleum-based fluid that is non-toxic.
- It is a phosphate ester-based fluid that is extremely irritating to human tissue. (Correct answer)
- It has a low viscosity and freezes at standard sea-level temperatures.
Correct answer: It is a phosphate ester-based fluid that is extremely irritating to human tissue.
Skydrol is a fire-resistant, phosphate ester-based hydraulic fluid. While it has excellent properties for aviation use, it is known to be very irritating to the skin and eyes, requiring the use of appropriate PPE like gloves and goggles during handling.
Question 6: In a pneumatic system, what is the primary purpose of a moisture separator or chemical dryer component?
- To add lubrication to the compressed air.
- To increase the pressure of the system.
- To cool the compressed air before it enters the system.
- To remove water vapor and prevent corrosion or freezing. (Correct answer)
Correct answer: To remove water vapor and prevent corrosion or freezing.
As ambient air is compressed, its temperature rises, and it can hold more moisture. When the air cools, this moisture condenses. A moisture separator and/or chemical dryer (desiccant) is installed downstream of the compressor to remove this water vapor, preventing it from causing corrosion or freezing in the pneumatic lines and components.
