MEOC Hydraulic Systems & Fluid Management

Question 1

What is the primary function of the hydraulic system in a mini excavator?

Accepted Answer

To convert engine power into pressurized fluid force for operating attachments and travel

Answer

To provide electrical power to the machine control panel

Answer

To regulate engine cooling system temperature

Answer

To control fuel injection timing and throttle response

Question 2

Which hydraulic fluid specification is most commonly required for mini excavators operating under standard US conditions?

Accepted Answer

ISO VG 46 or ISO VG 68 hydraulic oil

Answer

Engine oil SAE 30W

Answer

Automatic transmission fluid (ATF) Type A only

Answer

Gear oil GL-5 80W-90

Question 3

What is 'cavitation' in a mini excavator hydraulic system?

Accepted Answer

Formation of vapor bubbles in fluid due to localized low pressure, causing component damage

Answer

Excessive pump pressure damaging cylinder seals

Answer

Hydraulic fluid thickening in cold temperatures

Answer

A relief valve opening too frequently under high load

Question 4

What is the purpose of the hydraulic return filter on a mini excavator?

Accepted Answer

To remove contaminants from fluid returning to the reservoir

Answer

To boost fluid pressure before it reaches the main pump

Answer

To regulate hydraulic fluid operating temperature

Answer

To prevent hydraulic fluid from foaming during operation

Question 5

When should the hydraulic filter on a mini excavator be replaced?

Accepted Answer

At manufacturer-specified service intervals or when the restriction indicator signals restricted flow

Answer

Only after the machine shows obvious hydraulic performance symptoms

Answer

Every 10 operating hours regardless of condition

Answer

Only at the same time hydraulic fluid is fully drained and replaced

Question 6

What is the function of the hydraulic relief valve in a mini excavator?

Accepted Answer

To limit maximum system pressure by diverting fluid to the reservoir when pressure exceeds a preset value

Answer

To filter fine metal particles from hydraulic fluid

Answer

To increase hydraulic flow rate during heavy digging cycles

Answer

To cool hydraulic fluid by routing it through the heat exchanger

Question 7

Which symptom most strongly indicates air contamination in a mini excavator hydraulic system?

Accepted Answer

Spongy, jerky, or inconsistent movement of boom, arm, or bucket functions

Answer

Hydraulic fluid appearing noticeably darker than normal

Answer

Reduction in engine fuel consumption during normal operation

Answer

Overheating of the engine coolant system