T3

Question 1

What is sludge?

Answer 1

A thick gel-like two-phase substance composed of liquid and solid particles

Question 2

Two situations where fluid temperature increases

Answer 2

-Increases during operation due to pressurization of the oil
-Increases when the fluid expands as it leaves the pressure relief valve

Question 3

State the main difference between absorbent and adsorbent depth-type filters.

Answer 3

-Absorbent filters mechanically trap contaminants in oil
-Adsorbent filters mechanically trap contaminants and chemically remove them

Question 4

Why are absorbent filters not used in hydraulic systems?

Answer 4

They may remove important additives from oil

Question 5

What are filter condition indicators?

Answer 5

They sense the pressure difference between the filter inlet and outlet.

Question 6

Where are filters placed in a hydraulic circuit?

Answer 6

-Pump inlet
-Working lines between pump and actuator
-On the return line before entering the reservoir

Question 7

What is the main difference between sump strainers and suction filters in terms of their location?

Answer 7

-Sump strainers are installed at the pump inlet
-Suction filters are installed above the fluid level in the tank.

Question 8

Why should suction filters be carefully inspected and replaced once clogged?

Answer 8

The clogged filter causes more reduction to the vacuum pressure at the pump inlet.

Question 9

List 3 types of heat exchangers used in a hydraulic system.

Answer 9

-Radiators and finned conductors
-Shell and tube
-Immersion heat exchangers

Question 10

How is the housing of working line filters different from return line filters?

Answer 10

The housing of working line filters are designed to stand the high working fluid pressure.

Question 11

What is the purpose of fins on some types of heat exchangers?

Answer 11

The fins increase the exposed surface area for more heat transfer.

Question 12

Which is more efficient in transferring heat: Liquid to liquid or air to liquid heat exchangers?

Answer 12

Liquid to liquid

Question 13

Why are immersed electric heaters equipped with thermostats?

Answer 13

To limit the amount of heat delivered to the fluid. This helps avoid overheating.

Question 14

What are two ways by which contaminants enter the system during operation?

Answer 14

1. Dust may enter the system during rod retraction
2. Dust and moisture could enter through the tank breather

Question 15

What should be done to the system to ensure an adiabatic process?

Answer 15

The system should be perfectly insulated so no heat transfer is allowed.

Question 16

What are the four main processes required for conditioning air?

Answer 16

-Removing entrapped dirt
-Removing water vapour
-Removing thermal energy
-Adding oil for component lubrication

Question 17

Which carries less humidity; warmer or cooler air

Answer 17

Cooler air

Question 18

What happens to excess amounts of water if the humidity is at 100%?

Answer 18

The excess amount of water condenses as water droplets

Question 19

Should the lubricating oil be introduced between the compressor and the receiver?

Answer 19

No, it should be introduced before entering the working station

Question 20

What is an isothermal process?

Answer 20

If heat is removed during the compression, temperature stays constant

Question 21

What is an adiabatic process?

Answer 21

The process in which heat is not exchanged with the system.

Question 22

5 main layers of the atmosphere

Answer 22

-Exosphere
-Thermosphere
-Mesosphere
-Stratosphere
-Troposphere

Question 23

What is the approximate percentage of nitrogen and oxygen by volume at the sea level in the atmosphere?

Answer 23

78% Nitrogen
21% Oxygen

Question 24

What is the main difference between a pressure relief valve and a sequence valve in terms of drain?

Answer 24

Sequence valves always have an external drain line.

Question 25

What are the most common types of shutoff valves?

Answer 25

-Globe
-Gate
-Ball
-Spool and needle

Question 26

What are the two most common types of check valves?

Answer 26

In line and right angle

Question 27

List the two types of flow control devices

Answer 27

Restrictor and bypass control

Question 28

3 Types of gas charged accumulators

Answer 28

-Piston
-Bladder
-Diaphragm

Question 29

Why should only inert gas be used in gas charged accumulators?

Answer 29

Because they do not react to the rubber layer or oil if exposed to the oil

Question 30

List the 5 most common center positions in a four way three position

Answer 30

-Closed center
-Open center
-Tandem center
-Floating center
-Regenerative center

Question 31

Two functions the stored energy in accumulators could be used in

Answer 31

-Maintain system pressure
-Supplying fluid to other secondary circuits when a pump is down

Question 32

What are three parameters that characterize accumulators?

Answer 32

-Weight loaded
-Spring loaded
-Gas charged

Question 33

Why is a spring loaded poppet is installed at the oil port in bladder accumulators?

Answer 33

To prevent the bladder from moving into the poil port if the gas pressure excessively surpasses oil pressure

Question 34

How would temperature change with rapid charging of gas accumulators?

Answer 34

It causes the gas molecules to have more friction, leading to increased temperature

Question 35

Classify DCV’s based on how the flow is directed

Answer 35

-Shutoff valves
-Check valves
-Three way valves
-Four way valves