Hydraulics and Pneumatics Flashcards
7 cards from real AMT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Hydraulics and Pneumatics flashcards as text
What effect does elevated temperature have on hydraulic fluid viscosity?
Answer: Viscosity decreases, potentially causing increased leakage and wear
Higher temperatures reduce hydraulic fluid viscosity, which can increase internal leakage past seals and accelerate component wear.
What is cavitation in a hydraulic pump?
Answer: Formation and collapse of vapor bubbles due to localized low pressure, causing erosion and noise
Cavitation occurs when fluid pressure drops below vapor pressure, forming bubbles that violently collapse and erode metal surfaces inside the pump.
In aircraft pneumatic systems, what is the most common source of high-pressure air?
Answer: Engine bleed air tapped from the compressor stages
Most aircraft pneumatic systems are supplied by bleed air extracted from intermediate or high-pressure compressor stages of the turbine engines.
What does an aircraft hydraulic power transfer unit (PTU) do?
Answer: Uses pressure from one hydraulic system to drive a pump that pressurizes another system without fluid transfer
A PTU uses one system's hydraulic pressure to drive a hydraulic motor/pump combination that pressurizes another system, keeping the two fluid circuits separate.
What is the purpose of a hydraulic fuse?
Answer: To automatically shut off fluid flow when flow rate exceeds a set value, limiting fluid loss from a ruptured line
A hydraulic fuse senses abnormally high flow (indicating a burst line) and closes automatically to conserve remaining fluid and maintain pressure to other actuators.
Which type of seal material is NOT compatible with phosphate ester (Skydrol) hydraulic fluid?
Answer: Buna-N (nitrile rubber)
Nitrile (Buna-N) seals are compatible with petroleum-based fluids but swell and degrade rapidly when exposed to Skydrol phosphate ester fluid.
What is the purpose of a priority valve in an aircraft hydraulic system?
Answer: To ensure essential services (such as flight controls) receive hydraulic pressure before less critical systems during low-pressure conditions
A priority valve opens only when system pressure exceeds a set threshold, ensuring critical systems like flight controls are satisfied before secondary systems receive flow.