Hydraulics and Pneumatics Flashcards

What is the purpose of a hydraulic system relief valve?

Answer: To limit maximum system pressure and prevent overpressure damage

A relief valve limits maximum system pressure by bypassing fluid back to the reservoir when pressure exceeds the set value.

Which hydraulic fluid is used in most modern commercial transport aircraft?

Answer: Skydrol (purple phosphate ester)

Skydrol (phosphate ester-based) is used on most commercial transports because of its fire-resistant properties.

In a hydraulic system, what does a check valve do?

Answer: Allows fluid flow in one direction only

A check valve permits fluid flow in only one direction, preventing backflow that could cause loss of pressure or actuator drift.

What type of pump is most commonly used as the main hydraulic pump on large transport aircraft?

Answer: Variable-displacement axial piston pump

Variable-displacement axial piston pumps are preferred because they maintain constant pressure by adjusting displacement rather than bypassing excess flow.

What is the function of a hydraulic accumulator?

Answer: To store a small volume of pressurized fluid for emergency use and dampen pressure surges

An accumulator stores pressurized fluid to supplement pump output during peak demand, provide emergency power, and absorb pressure surges.

When bleeding a hydraulic system, what is the primary goal?

Answer: Purge all air from the lines to prevent spongy actuator response

Bleeding removes entrapped air from hydraulic lines; air is compressible and causes spongy, unpredictable actuator movement.

A selector valve in a hydraulic system is used to:

Answer: Direct fluid flow to the appropriate actuator port to control direction of movement

A selector (directional control) valve routes pressurized fluid to one side of an actuator while connecting the opposite side to return, reversing actuator direction.