310T Hydraulic Systems

Question 1

A hydraulic lift gate on a truck drops slowly under load even though the pump motor runs continuously. What is the MOST likely cause?

Accepted Answer

A worn or bypassing hydraulic pump

Answer

Low hydraulic fluid level

Answer

A blocked filter restricting return flow

Answer

An incorrectly adjusted relief valve set too high

Question 2

Which hydraulic fluid property is MOST important when selecting fluid for a truck system that operates in both extreme cold and high-temperature conditions?

Accepted Answer

Wide viscosity index (VI)

Answer

High flash point

Answer

High water content tolerance

Answer

Low specific gravity

Question 3

When inspecting a hydraulic cylinder that is leaking past the rod seal, a technician notices the rod surface has a spiral groove worn into it. What caused this damage?

Accepted Answer

Contaminated hydraulic fluid containing abrasive particles

Answer

Over-pressurization of the cylinder

Answer

Incorrect rod material for the application

Answer

Excessive extension speed causing hydraulic hammer

Question 4

A technician is bleeding a hydraulic braking system on a coach. What is the correct procedure to ensure all air is removed?

Accepted Answer

Bleed only the wheel cylinder furthest from the master cylinder first

Answer

Start at the caliper closest to the master cylinder and work outward

Answer

Begin at the highest point in the system and work downward, ending at the master cylinder

Answer

Crack all bleed screws simultaneously and apply steady pressure until fluid runs clear

Question 5

What does a hydraulic system relief valve do when system pressure reaches its set point?

Accepted Answer

It bypasses excess fluid back to the reservoir to limit maximum system pressure

Answer

It shuts off the pump motor to prevent over-pressurization

Answer

It opens a secondary circuit to share load with another pump

Answer

It closes the main control valve to stop cylinder movement

Question 6

A hydraulic pump produces adequate flow at low speed but cavitates at high engine RPM. What is the MOST likely cause?

Accepted Answer

A restricted inlet (suction) line or clogged suction strainer

Answer

A failed pressure relief valve stuck open

Answer

Excessive pump output pressure exceeding system rating

Answer

Air trapped in the hydraulic reservoir