433A Hydraulic Systems 2

Question 1

What is cavitation in a hydraulic pump?

Accepted Answer

Formation and collapse of vapor bubbles in the fluid due to low inlet pressure

Answer

Cavitation occurs when inlet pressure drops below the fluid's vapor pressure, causing dissolved gases and vapor to form bubbles. These bubbles collapse violently when they reach higher-pressure zones, eroding metal surfaces and causing severe pump damage.

Question 2

What is the difference between a fixed displacement pump and a variable displacement pump?

Accepted Answer

A fixed pump delivers the same volume per revolution regardless of pressure, while a variable pump can adjust its output volume

Answer

A fixed displacement pump delivers a constant volume of fluid per revolution. A variable displacement pump can change its output volume per revolution, typically by adjusting the swashplate angle, allowing flow to match demand and improving energy efficiency.

Question 3

Why is the viscosity of hydraulic fluid critical to system performance?

Accepted Answer

If too thin, internal leakage increases and lubrication is poor; if too thick, flow resistance and cavitation risk increase

Answer

Viscosity that is too low causes excessive internal leakage, poor lubrication, and wear. Viscosity that is too high increases flow resistance, pressure losses, causes sluggish operation, and increases cavitation risk at the pump inlet.

Question 4

What type of hydraulic valve uses a spool to direct fluid flow?

Accepted Answer

Spool-type directional control valve

Answer

A spool-type directional control valve uses a precision-machined spool that slides within a bore to connect or block fluid passages, directing flow to and from actuators. The spool may be shifted by solenoids, pilot pressure, or manual levers.

Question 5

What is the purpose of a counterbalance valve in a hydraulic circuit?

Accepted Answer

To prevent uncontrolled movement of a load that could overrun the pump flow, such as lowering a heavy load

Answer

A counterbalance valve prevents a gravity or momentum load from overrunning the hydraulic pump by creating a back-pressure on the actuator's return port. This ensures smooth, controlled lowering of heavy loads.

Red Seal Millwright 433A Practice Test

Red Seal Millwright 433A Practice Test

433A Hydraulic Systems 2