AMT Hydraulics and Pneumatics Questions and Answers 1 — Questions and Answers
Question 1: An aircraft's hydraulic system utilizes a component to ensure the landing gear doors are fully open before the landing gear begins to extend. What is this component called?
- A check valve
- A pressure relief valve
- A sequence valve (Correct answer)
- An orifice restrictor
Correct answer: A sequence valve
A sequence valve is designed to control the order of operations in a hydraulic circuit. In the context of landing gear, it ensures that one action (doors opening) is completed before the next action (gear extending) begins.
Question 2: Which of the following is a primary advantage of using a phosphate ester-based hydraulic fluid, such as Skydrol, over a mineral-based fluid in modern transport category aircraft?
- Lower cost and wider availability
- Compatibility with natural rubber seals
- Superior fire resistance (Correct answer)
- Reduced toxicity and environmental impact
Correct answer: Superior fire resistance
Phosphate ester-based hydraulic fluids like Skydrol are widely used in commercial aviation primarily because of their excellent fire-resistant properties, which enhance safety in high-temperature and high-pressure hydraulic systems.
Question 3: A technician is servicing a hydraulic accumulator that is part of an aircraft's main hydraulic system. What is one of the primary functions of this component?
- To filter contaminants from the hydraulic fluid
- To cool the hydraulic fluid as it returns to the reservoir
- To mix air with the fluid to improve compressibility
- To store hydraulic fluid under pressure to supplement the pump during peak demand (Correct answer)
Correct answer: To store hydraulic fluid under pressure to supplement the pump during peak demand
Hydraulic accumulators store incompressible fluid under pressure from an external source, typically compressed nitrogen. This stored energy is used to supplement the hydraulic pump during periods of high demand, dampen pressure surges, and provide emergency pressure if the pump fails.
Question 4: The fundamental principle that allows hydraulic systems to transmit and multiply force is known as:
- Bernoulli's Principle
- Pascal's Law (Correct answer)
- Newton's Third Law
- Boyle's Law
Correct answer: Pascal's Law
Pascal's Law states that a pressure change at any point in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. This principle allows a small force applied to a small area to generate a much larger force on a larger area.
Question 5: Compared to hydraulic systems, a primary characteristic of aircraft pneumatic systems is that they generally:
- Operate at much higher pressures
- Use a compressible fluid (air or nitrogen) (Correct answer)
- Provide more precise and smooth motion control
- Require a return line to the reservoir
Correct answer: Use a compressible fluid (air or nitrogen)
Pneumatic systems use a compressible gas, such as air or nitrogen, as the working fluid. This is a key difference from hydraulic systems, which use incompressible liquids. The compressibility of air results in less precise motion control compared to hydraulics.
Question 6: A technician is troubleshooting a high-pressure pneumatic system. Which of the following is a significant safety hazard specifically associated with compressed air or nitrogen that is not typically a concern with hydraulic fluid?
- System contamination from moisture
- The potential for fire if a leak occurs near an ignition source
- Skin irritation upon contact
- Injection of gas into the bloodstream through a minor skin break (Correct answer)
Correct answer: Injection of gas into the bloodstream through a minor skin break
A unique and severe danger of high-pressure pneumatic systems is the potential for compressed gas to be injected into the bloodstream through a cut or puncture in the skin. This can cause an air embolism, a dangerous medical condition that can be fatal.
