A&P Hydraulic and Pneumatic Systems Questions and Answers

Question 1

A technician observes that a hydraulic system's pressure gauge fluctuates rapidly and the system operates erratically, especially upon initial actuator movement. Which component is most likely failing to perform its function of dampening pressure surges?

Accepted Answer

Accumulator

Answer

A primary function of a hydraulic accumulator is to absorb pressure shocks and dampen fluctuations in the hydraulic system. An accumulator that has lost its nitrogen pre-charge or has a ruptured diaphragm/bladder cannot perform this function, leading to erratic pressure and jerky operation.

Question 2

Which of the following is the primary purpose of a hydraulic sequence valve in a landing gear system?

Accepted Answer

To ensure the gear doors are open before the gear begins to extend.

Answer

Sequence valves are used to control the order of operations in a hydraulic circuit. In a landing gear system, a sequence valve ensures that the gear doors are fully open before hydraulic pressure is directed to the landing gear actuator, preventing mechanical damage.

Question 3

A technician is servicing a large transport category aircraft hydraulic system that uses a purple-colored, phosphate-ester based fluid (Skydrol). What type of seal material MUST be used for components within this system?

Accepted Answer

Butyl rubber or Ethylene Propylene (EPDM)

Answer

Phosphate-ester based hydraulic fluids, such as Skydrol, are chemically incompatible with petroleum-based seals like Neoprene and Buna-N, which will swell and deteriorate rapidly. Systems using Skydrol require compatible seals made of materials like Butyl rubber or Ethylene Propylene Diene Monomer (EPDM).

Question 4

In a high-pressure pneumatic system, what is the primary function of a moisture separator?

Accepted Answer

To remove entrained water vapor to prevent freezing and corrosion.

Answer

When air is compressed, its temperature rises and its ability to hold moisture decreases, causing water vapor to condense. A moisture separator is designed to remove this liquid water from the pneumatic system to prevent it from freezing at high altitudes, which could block lines, and to prevent corrosion of system components.

Question 5

An aircraft hydraulic system is powered by a constant-displacement pump. To prevent pump and system overload when no services are being operated, what component diverts the full output of the pump back to the reservoir at low pressure?

Accepted Answer

Unloading valve

Answer

A constant-displacement pump moves a fixed volume of fluid with each revolution. An unloading valve is used to automatically divert the pump's output to the reservoir at low pressure when system pressure reaches a set point. This 'unloads' the pump, reducing power consumption and heat generation, while a check valve maintains pressure in the system. A pressure relief valve is a safety device for over-pressurization, not for normal unloading.

A&P - Certified Airframe and Powerplant Mechanics Practice Test

A&P - Certified Airframe and Powerplant Mechanics Practice Test

A&P Hydraulic and Pneumatic Systems Questions and Answers