301G: Hydraulic System Types

Question 1

A hydraulic system is defined as:

Answer 1

All of the interconnected hydraulic components mounted on a piece of equipment

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Question 2

A group of interconnected components within a hydraulic system that are intended to perform a specific function is called a:

Answer 2

Hydraulic circuit

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Question 3

Open centre hydraulic systems are sometimes called:

a) constant pressure systems
b) constant flow systems
c) variable flow systems
d) variable pressure systems

Answer 3

b) constant flow systems

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Question 4

One characteristic of open centre hydraulic systems is high system pressure when the directional control valve is in the neutral position. (T/F)

Answer 4

False

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Question 5

Open centre hydraulic systems are most often used in applications where:

a) high system efficiency is required
b) accurate motion control is a priority
c) hydraulic operations are not a high percentage of the machine’s duty cycle
d) the cost of the system components is not a concern

Answer 5

c) hydraulic operations are not a high percentage of the machine’s duty cycle

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Question 6

Constant horsepower open centre hydraulic systems maintain a constant power draw from the engine by varying:

Answer 6

Pump displacement proportional to the load on the system

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Question 7

Closed centre systems may be supplied with either a fixed or variable displacement pump. (T/F)

Answer 7

True

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Question 8

Why are closed centre systems equipped with pressure compensated pumps often called demand type hydraulic systems?

Answer 8

Oil flow is only
provided when it’s required to perform work

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Question 9

Why are load sensing hydraulic systems more efficient than other types of systems?

Answer 9

Provide as closely as possible the precise amount of flow and pressure required to perform the work.

Margin pressure

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Question 10

The difference between an open and closed circuit hydrostatic transmission is that the path of oil flow between the pump and motor is interrupted by the reservoir in the open circuit. (T/F)

Answer 10

True

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Question 11

The most commonly used HST in mobile heavy equipment is a/an:

a) open circuit system with a fixed displacement pump
b) open circuit system with a variable displacement pump
c) closed circuit system with a variable displacement, reversible pump
d) closed circuit system with a fixed displacement pump

Answer 11

c) closed circuit system with a variable displacement, reversible pump.

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Question 12

On HST systems that are equipped with variable displacement motors, motor torque generation will:

a) remain the same regardless of motor displacement
b) be reduced as motor displacement is reduced
c) be increased as motor displacement is reduced
d) be reduced as motot displacement is increased

Answer 12

b) be reduced as motor displacement is reduced

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Question 13

List five advantages of hydrostatic transmissions

Answer 13

a) infinite motor speed control from maximum to zero in both directions of rotation
b) accurate motor speed can be maintained regardless of the load on the motor output shaft
c) quicker response to speed and direction changes than any other type of transmission
d) provides a hydrostatic lock of the motor when the output shaft speed is at zero
e) the load cannot overrun the motor when the load is being decelerated (a form of dynamic braking)

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Question 14

A pilot control circuit is a low-pressure hydraulic circuit used to remotely operate a directional control valve. (T/F)

Answer 14

True

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Question 15

What two valves make up a basic load sensing control for a variable displacement pump?

Answer 15

• Load sence valve
• Pressure limiting valve

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Question 16

Wheel Loader Hydraulic Schematic

What is valve #6?

Answer 16

Pressure reducing valve for pilot circuit

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Question 17

Wheel Loader Hydraulic Schematic

What are valves #9?

Answer 17

Pilot control valves

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Question 18

Wheel Loader Hydraulic Schematic

What is valve #10?

Answer 18

System relief valve

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Question 19

Wheel Loader Hydraulic Schematic

If the bucket, boom, and auxillary control valves were all moved at the same time, which circuit would receive priority?

Answer 19

Bucket circuit, due to the series passageway arrangement. Oil flow from the bucket function returns to reservoir and is not available to the other functions.

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Question 20

Wheel Loader Hydraulic Schematic

What is valve #10?

Answer 20

Relief valve

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Question 21

Wheel Loader Hydraulic Schematic

What is valve #15?

Answer 21

Anti-Cavitaion check valve

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Question 22

Wheel Loader Hydraulic Schematic

What is valve #16?

Answer 22

Regeneration & check valve.
Work together to allow return oil from bucket cylinder base end to supplement pump oil flow to cylinder rod end when in full dump position.

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Question 23

Wheel Loader Hydraulic Schematic

What is component #17?

Answer 23

Return filter & bypass valve

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Question 24

Wheel Loader Hydraulic Schematic

What are the four positions of the boom directional control valve?

Answer 24

• Hold
• Raise
• Lower
• Float

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Question 25

Wheel Loader Hydraulic Schematic

What is the function of check valves #5?

Answer 25

• Supply pilot system with oil from either the steering pump or loader pump depending on which is operating at the higher pressure.
• Prevent leakage between the loader and steering systems

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