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Millwright Third Block NS > week 5 > Flashcards

week 5 Flashcards

1
Q

What are the 2 types of actuators?

A
  • Linear (cylinder)

- Rotary (Motor)

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2
Q

What creates pressure?

A

Resistance to flow.

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3
Q

What is the “job” of the pump?

A

The create flow.

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4
Q

What are the two types of pumps?

A
  • Fixed Displacement

- Positive or variable displacement.

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5
Q

What does the pump do?

A

Converts mechanical force and motion into fluid power.

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6
Q

What is the primary function of a control valve?

A

To control pressure which may include pressure reducing or flow control.

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7
Q

Advantages of Hydraulics

A
  • Variable Speed
  • Reversible
  • Overload Protection
  • Small Packages
  • Can be Stalled
  • Absence of Vibration
  • Quiet Operation
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8
Q

Disadvantages of Hydraulics?

A

Oily and messy
Catastrophic failure, bursting of lines and loss of control.
Noisy
Combustability of oils, very hot.

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9
Q

What are the 4 basic principles of hydraulics?

A
  • Liquids have no shapes of their own.
  • Liquids are practically incompressible.
  • Liquids transmit applied pressure in all directions.
  • Liquids provide great increases in work force.
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10
Q

What is the purpose of the fluid?

A
  • Power transmission
  • Lubrication
  • Seal clearances
  • Cooling
  • Dissipate Heat
  • inhibit rust corrosion
  • act as a brake when required
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11
Q

What is the basic function of Pilot lines?

A

Transmits fluid pressure to control another device.

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12
Q

What is the basic function of Working lines?

A

To carry the fluid (pressure) doing the work.

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13
Q

State Pascal’s Law.

A

Pressure applied on a confined fluid is transmitted undiminished in all directions, acts with equal force on equal areas, and at right angles to them.

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14
Q

define pressure

A

To determine the total force exerted on a surface, it is necessary to know the pressure of force on a unit of area.

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15
Q

What is meant by “conservation of energy”?

A

What is gained in force must be sacrificed in distance.

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16
Q

What is the output component of a hydraulic system named?

A

Actuator

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17
Q

What is the input component of a hydraulic system named?

A

Pump

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18
Q

Name 3 advantages of a Hydraulics system.

A
  1. High Power/Large load capacity
  2. Precise positioning
  3. Smooth movement
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19
Q

What is the origin of the term “hydraulics”?

A

From Greek words that mean “water” and “pipe”.

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20
Q

What makes petroleum oil suitable as a hydraulic fluid?

A
  • It is minimally compressible (0.5% @ 1,000psi)

- Its lubrication abilities.

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21
Q

What can you say definitely about the pressures on opposite sides of an orifice when oil is flowing through it?

A

The pressure is different, i.e. there is a pressure drop.

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22
Q

What pressure is usually available to charge

the pump inlet?

A

the inlet of a pump normally is charged with oil by a difference in pressure between the reservoir and the pump inlet. most pump manufacturers recommend a vacuum of no more than 5 inches of mercury, 12.2 psia.

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23
Q

Why should the pump inlet vacuum be minimized?

A

to create flow

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24
Q

What is the function of the pump?

A

to create flow

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25
Q

Why is loss of pressure usually not a symptom of pump malfunction?

A

Because pressure can be lost only when there is a leakage path that will divert all the flow from the pump.

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26
Q

How is pressure created?

A

Resistance to flow.

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27
Q

What determines the speed of an actuator?

A

Its size and the rate of oil flow into it.

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28
Q

Air entrainment — Air in the fluid will cause

A

poor (slow) performance

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29
Q

Charles Law

A

The volume of a gas at a constant pressure is directly proportional to its absolute temperature.

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30
Q

Vapor pressure:

A

Pressure at which a liquid boils for a specific temp.
The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced.

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31
Q

Advantages of fluid power

A

Ease and accuracy of control.
Multiplication of force.
Constant force of torque.
Simplicity, safety, and economy.

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32
Q

What is the prime mover?

A

Whatever drives the pump

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33
Q

Conservation of Energy

A

Energy cannot be created nor destroyed

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34
Q

Properties of Hydraulic Fluids

A 
viscosity
lub
film str.
pour point
flash point
demulsibilty
resis to foam
chem stability
anti wear properties
compressibility
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35
Q

if the gpm is constant but the pipe diameter changes what happens to the flow velocity?

A

as the diameter decreases flow velocity increases and vise versa

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36
Q

if the pipe diameter stays constant but the gpm changes what happens to the flow velocity?

A

as the gpm decreases the flow velocity decreases and vise versa

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37
Q

Pressure is created either by

A

resistance to flow, referred to as dynamic pressure, or by the potential energy of an object being affected by gravity, known as static pressure.

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38
Q

Viscosity

A

Resistance to flow at a given temperature

**Single most important property of a hydraulic fluid

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39
Q

Too high of a viscosity causes:

A
  • High resistance to flow
  • Increased energy consumption due to increased friction
  • Increased input torque requirement at the pump
  • Slow or sluggish operation/actuation
  • Insufficient separation of air from the oil in the reservoir
  • Pump cavitation
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40
Q

Too low of a viscosity causes:

A
  • Increased internal leakage
  • Excess wear
  • Decreased pump efficiency (volumetric) due to increased leakage and possible cylinder blow-by (could cause increased cycle times/slower machine operation)
  • Internal leaking causing an increase in operating temperature
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41
Q

Absolute Viscosity

A

Resistance encountered when moving one layer of liquid over another.

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42
Q

Kinematic Viscosity

A

The amount of time needed for a fixed volume of oil to flow through a capillary tube.

43
Q

Temperature adversely affects:

A
  • Specific weight
  • Specific gravity
  • Viscosity
44
Q

Purpose of valves

A
  • Regulates pressure
  • Controls fluid rate
  • Controls direction of fluid movement
45
Q

Why does a piston retract faster than it extends?

A

Due to less volume to fill up the same amount of horsepower.

46
Q

Pumps

A
  • Convert mechanical energy into hydraulic energy

- Pumps do not generate or manipulate operating pressure in a hydraulic system - they produce flow

47
Q

Pumping Theory

A
  • Partial vacuum is created at inlet
  • Atm. pressure pushes fluid out of the reservoir and into pump intake
  • Mechanically, the pump pushes the fluid out of the discharge
  • Pumps create flow and pressure as a result of the resistance to that flow
48
Q

Pump Classifications

A

Positive Displacement

Non-positive Displacement

49
Q

Positive Displacement

A

Delivers the same amt. of fluid per shaft revolution despite the outlet flow of pressure

50
Q

Non-positive Displacement

A

Flow rate varies greatly with changes in resistance flow

51
Q

if viscosity is too low

A
  • internal and external leakage will increase.
  • pump slippage will increase and reduce pump efficiency and increase oil temperture
  • the system will operate at lower pressure
  • there will be a loss of precise control.
52
Q

if viscosity is too high

A
  • component and fluid temp will increase.
  • operation will be sluggish
  • pressure drops throughout the system will increase
53
Q

names sources of contamination:

A
  • Built in dirt produced during repairs
  • Ingress of rust, paint, etc from tank or reservoir
  • generated in pump, valves, etc
  • ingress from cylinder oil seals
  • ingress from new oil and refill of oil.
54
Q

hydrostatic- positive displacement-

name reciprocating pumps properties

A

hi press low speed 250/ 500 strokes/min up to 700 bar

55
Q

name three rotary positive displacement pump

A
  • gear- high speed, high volume, low pressure
  • vane- low pressure
  • piston- high pressure
56
Q

name two hydrodynamic non- positive displacement pumps

A

centrifugal

axial flow

57
Q

DCV do what

A

start, stop, and control the direction of flow

58
Q

there will always be a small internal leak in the direction control valve. This leak is dependent upon:

A
  • the gap between the spool and the body
  • the length of the gap
  • the viscosity of the oil
  • the pressure difference between the connections
59
Q

a relief valve does what and how

A

it is used to limit the pressure in the system to a preset maximum pressure. this is done by diverting some or the entire pump output to the tank when the pressure setting is reached

60
Q

relief valve normally open or closed

A

closed

61
Q

pressure reducing valve normally open or closed

A

open

62
Q

a pressure reducing valve does what and how

A

they are used to maintain reduced pressure in certain parts of the system. they are actuated by pressure and tend to close as the pressure reaches the valve settings.

63
Q

a unloading valve does what and how

A

the unloading valve is often used in systems with two or more pumps. it can unload one pump when the required system pressure is achieved. normally the valve is closed but it opens when the pilot pressure is equal or higher than the preset opening pressure of the valve.

64
Q

counterbalance valve normally open or close

A

both one in each direction

65
Q

a counterbalance is used to

A
  • prevent creeping of heavy loads
  • prevent overload
  • prevent overspeeding and runaway loads.
  • prevent accidents if pipes or hoses break.
66
Q

what does a counterbalance valve do

A

They are designed to create backpressure at the return line of the actuator to prevent losing control over the load.

67
Q

name some basic cylinder construction

A
  • tie rod
  • rod bearing
  • rod wiper
  • rod seal
  • rod end head
  • rod end port
  • piston rod
  • body
  • air vent
  • cushion collar
  • piston seals
  • cap end head
  • cap end port
  • piston
  • static seal
  • cushion plunger
68
Q

what is the difference between motors and pumps in a hydraulic system?

A

the pump moves the fluid

the fluid moves the motor

69
Q

75 percent of hydraulic failures are due to what?

A

the hydraulic oil being in poor conditions

70
Q

name points of inspection for hydraulic systems

A
  • oil level
  • suction strainer
  • all filters
  • mounting bolts and brackets
  • operating pressures
  • oil leaks
  • oil temperatures
  • speed of the pump
71
Q

what are three main causes of hydraulic problems:

A

contamination
heat
leaks

72
Q

name some other problems

A
  • solenoids not operating
  • electrical source not operating
  • relief valve, counterbalance valves, set wrong
  • human error
73
Q

leaks can affect hydraulic system operation in three ways

A
  • actuators move slowly
  • maximum available system pressure may be reduced.
  • actuators may move when they should not.
74
Q

What are three (3) ways to push fluid into a pump besides using atmospheric pressure?

A
  • Gravity
  • Pressurized Reservoir
  • Charge Pump
75
Q

What is the basic operating principle of any positive displacement pump

A

Pumping chambers increase in volume at the inlet and then decrease as they push the fluid out the discharge ports.

76
Q

What, if any, change should you expect in the output of a positive displacement pump as the backpressure increases?

A

Small Decrease.

77
Q

What condition occurs when the inlet flow is less than the discharge?

A

Cavitation.

78
Q

List three (3) methods of ensuring adequate inlet flow?

A
  • Gravity
  • Pressurized Reservoir
  • Charge Pump
79
Q

Which seals are contained in the rod bushing?

A

Rod wiper seals and pressure seals.

80
Q

Why is an ORB fitting preferable to a tapered thread fitting?

A

It causes less stress and distortion.

81
Q

How can you detect an internal leak in a cylinder?

A

By hot spots.

82
Q

What is the operating principle of any hydraulic motor?

A

Fluid pushes on vanes, gear teeth or pistons to turn the drive the shaft.

83
Q

Which three (3) types of motors are used for low speed and high torque?

A
  • Radial Piston.
  • Cam-Type Radial Piston.
  • Roller Vane Gerotor.
84
Q

What does a decease in mechanical efficiency indicate?

A

An increase in internal friction.

85
Q

What does a decrease in volumetric efficiency indicate?

A

Internal Leakage.

86
Q

On which two (2) factors does motor speed depend on?

A
  • Displacement

* Flow Rate

87
Q

the minimum horsepower rating of the prime mover can be calculated by what formula

A

hp = gpm by psi by .0007

88
Q

the horsepower rating of the prime mover can be calculated by what formula

A

hp = gpm by psi by .000583

89
Q

work equals what

A

force by distance

90
Q

increase the pressure setting on the motor

A

increase torque

91
Q

increase flow rate of motor

A

increase speed

92
Q

increase the displacement of the motor

A
  • decrease system pressure
  • decrease speed
  • increase torque
93
Q

What are the two type of check valves?

A

Pilot to open and pilot to close.

94
Q

force is commonly measured in

A

pounds or newtons

95
Q

pressure is commonly measured in

A
  • psi
  • bars
  • newtons per square meter = pascal
96
Q

work is commonly measured in

A

joules or foot-pounds

97
Q

1 watt is

A

1 newton lifted 1 meter in 1 second

98
Q

one hp is

A

33000 pounds lifted 1 foot in 1 minute

99
Q

746 watts is

A

1 hp

100
Q

1 watt is

A

.00134 hp

101
Q

energy cannot be destroyed, but it may be converted from one form to another.

A

this is the law of conservation of energy

102
Q

one imperial gallon equals

A

277 cu in.

103
Q

one us gallon equals

A

231 cu in.

104
Q

velocity is commonly expressed in

A

m/s

ft/s

Millwright Third Block NS (25 decks)

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