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HET3 > 301A: Hydraulic Principles > Flashcards

301A: Hydraulic Principles Flashcards

1
Q

List four advantages of hydraulic control in heavy equipment machinery
functions.

A

a) Relatively compact
b) Installation is more flexible than mechanical
c) Cooling and lubrication is easy to accommodate
d) Easily control several functions at one time

301A: Pg. 2

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2
Q

List four disadvantages of hydraulic control in heavy equipment machinery
functions.

A

a) Fluids under pressure can result in personal injury or death if not handled
safely.
b) There is always some noise produced by the system.
c) Oil leakage is a source of contamination and fire.
d) Temperature variations (too high or low) effect component reliability and
machine performance.

301A: Pg. 2

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3
Q

Work is defined as a:

A

Force acting through a distance

301A: Pg. 2

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4
Q

Force is the push or pull that is capable of producing or changing the motion of a body (T/F)

A

True

301A: Pg. 2

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5
Q

Energy is defined as:

A

The ability to do work

301A: Pg. 4

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6
Q

List four common forms of energy.

A

a) mechanical energy
b) hydraulic energy
c) heat energy
d) electrical energy

301A: Pg. 4

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7
Q

The law of conservation of energy states that:

A

Energy cannot be created or destroyed.

301A: Pg. 4

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8
Q

In an engine, chemical energy in the fuel is converted to mechanical energy in the
engine combustion chamber. (T/F)

A

False; Chemical energy in the fuel is converted to heat energy in the
combustion chamber.

301A: Pg. 4

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9
Q

A hydraulic actuator converts energy from what form to what form?

A

Hydraulic energy into mechanical energy.

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10
Q

Kinetic energy in a hydraulic system is created by:

A

The rate of oil flow through a system

301A: Pg. 5

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11
Q

Potential energy in a hydraulic system is responsible for creating:

a) force
b) motion
c) actuator speed
d) mechanical energy

A

a) Force

301A: Pg. 5

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12
Q

Laminar flow refers to:

A

When oil flows through a system in straight parallel flow paths.

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13
Q

List three conditions that could result in turbulent flow.

A

a) Conductors that are too small.
b) Abrupt changes in conductor cross-section.
c) Abrupt changes in flow direction.

301A: Pg. 10

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14
Q

Excessively turbulent flow in a hydraulic system will result in excessive:

A

Pressure losses (lost as heat)

301A: Pg. 10

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15
Q

Hydraulic actuators that are connected in series will have the same pressure applied to each actuator. (T/F)

A

False; Pressure applied to each actuator will vary while flow remains constant.

301A: Pg. 12

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16
Q

Actuators connected in series provide:

A) High torque, limited speed
B) High torque, high speed
C) Limited torque, high speed
D) Low power losses

A

C) limited toque, high speed.

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17
Q

Describe the pressure and flow characteristics of a hydraulic circuit that has multiple
actuators connected in parallel.
a) Pressure characteristics are ________
b) Flow characteristics are__________

A

a) the same pressure is applied to each actuator.

b) the flow is split amongst the actuators.

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18
Q

Hydraulic fluids that have a low VI number:

A

have wide viscosity changes with temperature.

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19
Q

The oil characteristic that has the most significant effect on the oil’s lubricating
ability is:

A

viscosity.

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20
Q

Two (2) conditions that indicate that an oil is excessively oxidized are:

A

a) the oil will have a burnt odour.

b) the oil will have a watery feel.

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21
Q

State the two (2) conditions that a hydraulic fluid must meet in order to be classified as biodegradable

A

a) 70 - 80% of the base fluid must be able to be broken down by micro-organisms.
b) The fluid must not harm living organisms.

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22
Q

Why is it a common service procedure to replace the hydraulic filter on a new piece
of machinery after about 100 hours of operation?

A

To remove built-in contamination from the system.

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23
Q

List four (4) entry points of ingressed contamination.

A

a) reservoir air breathers
b) pump inlet leakage
c) cylinder seals
d) unclean maintenance procedures.

24
Q

A rapid total disabling of a system or component is known as an:

A

catastrophic failure.

25
Q

Degradation failures are caused by _________

A

gradual surface wear.

26
Q

What type of contamination comes from external sources?

A

Ingressed

27
Q

What type of contamination could be drawn in by leakage at the pump inlet?

A

Air

28
Q

Will hydraulic cylinder seals and wipers remove all fine contaminants from the rod as it retracts?

A

No. Particles larger than 10 µm (microns) will be brought into the system through ingress contamination

29
Q

What is internally generated contamination?

A

It refers to particles the break loose from internal surfaces of hydraulic components.

30
Q

Internally generated particles come from where?

A

Possibly every component in the system.

31
Q

What are three types of failures of hydraulic components related to contamination?

A

Catastrophic failure intermittent failure degradation failure

32
Q

Small particles blocking a relief valve poppet could cause?

A

Relief valve to not move and resulting overpressure could sheer drive shafts or split pump housing’s

33
Q

Why is it intermittent failure sometimes called transient failure?

A

Because the problem often moves from component to component. Often self-correcting which makes it difficult to troubleshoot

34
Q

What is a characteristic of degradation failure?

A

It will result in excessive internal leakage and progress to catastrophic failure.

35
Q

What is a synthetic fire resistant hyd fluid made up of?

A

It is made up of chemically remanufactured ester fluids. Most common is phosphate ester fluid.

36
Q

Name the advantages synthetic fire resistant fluids have over water based.

A

They can operate at higher pressures.
They offer greatly improved lube qualities.
They are generally more fire resistant.

37
Q

What 2 conditions must oil meet to be qualified as a bio oil by ISO standards?

A

1) 70-80% must be able to be broken down by micro organisms within a set period of time.
2) must not harm living organisms.

38
Q

What is a problem with vegetable oils being used as a hydraulic fluid?

A

They oxidize rapidly when exposed to temps above 60c (140f)

39
Q

There are some problems associated with ester hyd fluids, they are:

A

They produce acids that damage system components. Nitrile rubber must be replaced with Viton seals.
They react with metals in the system. Particularly zinc, brass and bronze.
Very expensive.

40
Q

Proper hydraulic fluid should be chosen after considering:

A

Manufacturers specifications
Ambient conditions
Compatibility

41
Q

There are many contaminants in a system, name some possibilities.

A

Foreign liquids - water and acids
Metallic particles - iron, steel, aluminum and brass
Non metallic particles - dirt, rubber, lint and flakes of paint

42
Q

There are always contamination built into a system. T/F

A

True. This is why it is recommended that an oil change be done within a machines first 100 hours.

43
Q

Two hydraulic motors are connected in parallel.The parallel circuit divides what between the two motors?

A

oil flow

44
Q

Hydraulic oils can be divided into three general categories. They are:

A
  • Petroleum-based
  • Fire resistant
  • Biodegradable
45
Q

What is Bernoulli’s principle?

A

Bernoulli’s principle states that as the velocity of a fluid decreases the pressure exerted by the fluid increases

301A Pg. 7

46
Q

What is the formula for pressure?

A

Pressure = force/area

47
Q

What is the formula for flow rate

A

Flow rate = cylinder volume/time

48
Q

What is the formula for hydraulic pump output horsepower?

A

Kw = L/min * MPa * 0.0167

Hp = (gpm * rpm) / 1714

49
Q

How is hydraulic system efficiency determined?

A

By comparing the output power of a system to the power required to drive the system.

Efficiency of a pump = Actual output / Rated output

Greater than 80% efficiency is good for a pump

301A Pg. 9

50
Q

Power loss in a hydraulic system is manifested through what two forms?

A

Pressure Loss
- From not having laminar flow and backpressure

Flow loss
- From designed and unintended internal leakage

301A Pg. 9

51
Q

True or false

There must be a difference in potential energy in order for flow to occur in a hydraulic system

A

True

52
Q

The greater the pressure lost in the system, the more _____ will be generated

A

Heat

53
Q

Describe laminar flow

A

When oil moves through the system in straight parallel flow paths.

  • Conductors of adequate size
  • Smooth transition at bends/fittings
  • Gradual changes in piping direction

301A Pg. 9

54
Q

Most manufacturers recommend an oil VI of at least _____

A

90

301A Pg. 17

55
Q

What is added to oil which develops a protective film on moving parts?

A

Anti-wear additives

301A Pg. 17

56
Q

What is demulsification?

A

When water in oil separates out

HET3 (34 decks)

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