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Millwright Level 3 > Hydraulics > Flashcards

Hydraulics Flashcards

1
Q

This is required to move a stationary object or change how fast an object moves

A

Force (expressed in newtons or pounds)

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2
Q

Defined as the force per unit area

A

Pressure (expressed as N/m², psi, or bars) kPa or bars most common

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3
Q

Atmospheric pressure

A

14.7 psi (101.35 kPa, 1.01 bar)

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4
Q

Energy cannot be destroyed, but may be converted from one form to another

A

Law of conservation of energy

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5
Q

Unlike a gas, a liquid is virtually _______

A

incompressible

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6
Q

Hydraulic fluid compresses about __% at 1000 psi

A

1/2%

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7
Q

Pressure applied to a confined fluid at rest, force is transmitted equally in every direction and always at right angles to the containing surface

A

Pascal’s Law

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8
Q

How is flow rate expressed

A

litres per minute or gallons per minute

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9
Q

Refers to the average speed of the hydraulic fluid passing a given point. This is the distance travelled by the fluid in a unit of time

A

Velocity

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10
Q

The fluid moves in layers parallel to the walls

A

Laminar flow

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11
Q

When the fluid particles move in a random pattern

A

Turbulent flow (caused by high velocity, obstructions, sharp bends etc.)

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12
Q

The main causes of excessive friction in hydraulic lines

A

Excessive length of lines
Excessive velocity (lines too small)
Excessive number of bends or fittings
Sustained flow at high pressure

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13
Q

If the flow rate is constant, the sum of the kinetic energy and the potential energy at various points in the system is constant

A

Bernoulli’s Principle

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14
Q

Components of hydraulic systems that convert hydraulic energy into mechanical energy

A

Hydraulic actuators (cylinders for linear motion motors rotary motion)

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15
Q

If the cross-sectional area of the rod is more than half the piston face it is considered this

A

A ram (or plunger)

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16
Q

In a single-rod double acting cylinder which side is slower

A

Extension side is slower

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17
Q

What is the point of a cushion

A

Slows down the piston as it approaches the end of travel

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18
Q

Cylinder that has two pistons attached to one rod

A

Tandem

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19
Q

Pumps ____ the hydraulic fluid and motors are _____ by the hydraulic fluid

A

Drive, driven

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20
Q

How are DCVs numbered

A

3 /2 = 3 way valve (3 ports) with 2 positions

Spool types - sliding or rotary

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21
Q

These DCVs allow the spool to pass through from one envelope to another at any given rate

A

Throttling (infinite positioning). Indicated by parallel lines above and below the envelopes. Example is a Tracer valve

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22
Q

These DCVs snap into only one of the envelopes at a time

A

Non-throttling

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23
Q

DCV all ports are blocked off in neutral, locks actuator

A

Closed centre

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24
Q

DCV all ports are connected in neutral, actuator moves in direction of external forces

A

Open centre

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25
Q

DCV actuator ports are blocked off, flow from pump is back to the tank

A

Tandem centre

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26
Q

DVC ports A and B are connected to tank, and pump is blocked off, actuator coasts to a stop or moved manually

A

Float centre

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27
Q

DVC ports A and B are connected to pump, maintains constant pressure to both ports of actuator

A

Regenerative centre

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28
Q

Single position valves which allow free flow in one direction only

A

Check valve (common styles are ball or poppet)

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29
Q

Spring loaded check valves use a spring force of this

A

34kPa (5psi)

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30
Q

These valves control the hydraulic pressure in all or part of the circuit

A

Pressure control valve (one single square)

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31
Q

The difference between cracking pressure and full flow pressure is called this

A

Pressure override or pressure differential

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32
Q

The two basic designs of maximum pressure relief valves

A 
Direct acting (simple relief) valve
Pilot-operated (two stage)
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33
Q

Used if a large amount of fluid is to be relieved under a small pressure differential

A

Pilot-operated pressure relief valve

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34
Q

This valve returns pump output to the reservoir after the required system pressure has been reached

A

Unloading valve

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35
Q

Valves used to control vertical cylinders that are loaded so they don’t fall freely due to gravity

A

Counterbalance valve

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36
Q

The simplest and most finely adjustable type of throttle valve

A

Needle valve

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37
Q

A common method of controlling the amount of fluid passing through an orifice as the temperature changes

A

Temperature compensating rod

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38
Q

A magnet in which the magnetic lines of force are produced by an electric current

A

electromagnet (solenoid)

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39
Q

The solenoid-controlled pilot valve is called this

A

Master valve

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40
Q

This type of solenoid allows the operator to vary the position of the plunger by varying the amount of current to the solenoid

A

Proportional solenoids

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41
Q

Pressure in a hydraulic system is created by this

A

Resistance to flow (pump can produce flow but not pressure)

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42
Q

This type of filter has only a portion of oil passing through the filtering element

A

Proportional filter

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43
Q

This type of filter has all the oil pass through it

A

Full-flow (often has a bypass valve for when filter get clogged)

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44
Q

These filters are considered coarse filters or strainers

A

Mechanical (metal) filters (remove larger particles, not water or fine)

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45
Q

These filters contain paper, wood pulp, fabric or wool and remove fine particles and water

A

Absorbent (inactive) filters

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46
Q

These filters remove impurities by both mechanical and chemical means

A

Adsorbent (active). May also remove additives in hydraulic fluid

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47
Q

The smallest particle that can be seen

A

40 microns

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48
Q

The three positions for putting filters

A

Inlet side, pressure side, and return line side

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49
Q

The volume of fluid in the reservoir is normally equal to this

A

Two to three times the rated pump delivery for one minute

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50
Q

Recommended height of the baffle plate

A

Two-thirds the height of the minimum fluid level

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51
Q

Recommended height of the return and suction lines from the bottom of tank

A

1-1/2 to 2 times the pipe diameter

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52
Q

These store fluid under pressure for future use as a source of potential energy, as well as absorb shock waves

A

Accumulator

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53
Q

Three types of accumulators

A

Weight-loaded
Spring-loaded
Pneumatic or gas-charged (use Boyle’s law)

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54
Q

These operate as a force multiplier

A

Pressure intensifier

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55
Q

In hydraulic systems these three conditions are measured

A

Pressure, flow, and temperature

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56
Q

The most common electrical interface device found in hydraulic systems

A

Pressure activated electric switch

57
Q

The most common hydraulic fluid

A

Petroleum

58
Q

The heaviest of of hydraulic fluids and require special pump inlet designs

A

Synthetic

59
Q

What type of pipe should not be used

A

Galvanized because scales or flakes of zinc can enter system

60
Q

How should you seal a pipe connection

A

Starting 2 threads from the end of the pipe

61
Q

How is tubing sized

A

By the OD (fractions of an inch or dash numbers)

62
Q

SAE and JIC flare angles

A 
SAE = 45 (90 included angle)
JIC = 37 (74 included angle)
63
Q

The correct bend radius for tubing

A

3 to 4 times the tube OD

64
Q

The inner tube of a hose can withstand these temps

A

133 C (275F)

65
Q

Flow triangle equation

A

V
SA

V= Flow rate in inches cubed/minute
S= Speed in inches/minute
A= Area in inches square
66
Q

Type of relief valve commonly used in hydraulic systems operating above 500psi and flow above 3 gpm

A

Pilot-operated pressure relief valve (minimize pressure override)

67
Q

1 micron =

A

0.000039

68
Q

The flow paths in a valve are commonly called this

A

Ways

69
Q

When are pilot operated control valves necessary

A

To control direction of flows above 20 or 25 GPM

70
Q

Check valve gpm range

A

in-line = 100 gpm

right angle = 3 times as much as in-line

71
Q

The three flow control methods

A

Meter-in, meter-out, and bleed-off

72
Q

The two types of pressure compensators

A

Bypass and restrictor

73
Q

Capacity of screw and slip in cartridge valves

A

screw in = 30 to 35 gpm

slip in = over 30 gpm

74
Q

Conventional solenoid controlled valves are sometimes called this

A

Bang bang valves

75
Q

For proportional solenoids the movement is proportional to what?

A

The electrical input

76
Q

Gain output

A

1000000 the input voltage

77
Q

What does a servo valve use to operate the valve instead of a solenoid

A

A torque motor (much more accurate)

78
Q

The three types of servo valves

A

flapper nozzle, jet pipe, staging spool

79
Q

Three stage servos can handle flows as high as this

A

1000 gpm

80
Q

What do you call a cylinder with unequal area on each side

A

Differential cylinder

81
Q

The efficiency of a external gear motor should be at least this

A

85%

82
Q

The two classes of pumps in industry

A

Positive displacement and non-positive (dynamic)

83
Q

Which pumps are not suitable for hydraulic systems

A

Non-positive (dynamic)

84
Q

What does a positive displacement pump have that non-positive don’t

A

A positive seal between inlet and outlet

85
Q

Controlled leakage percentage in a positive displacement pump

A

5% to 15%

86
Q

Types of positive displacement pumps

A

Piston, vane, and gear

87
Q

Types of piston pumps (4)

A

in-line axial, bent axis, rotary, radial

88
Q

On a load sensing pump what is the standby pressure needed

A

200 to 400 psi

89
Q

Types of vane pumps

A
  • Balanced (two pumping chambers 180 degrees apart, displacement not adjustable)
  • Unbalanced (minimum 600rpm, must have large casing and bearings)
  • Cartridge
90
Q

Types of gear pumps

A

Internal gear and external gear

91
Q

Internal gear pump with star-shaped rotor

A

Gerotor (quietest gear pump)

92
Q

Efficiency of gear pumps and piston pumps

A 
Gear = 85%
Piston = 90-95%
93
Q

Which end of the pump is direction of rotation defined

A

Drive end

94
Q

Types of pressure control valves (5)

A 
Relief
Pressure reducing
Sequence
Counterbalance
Brake
95
Q

sometimes called a hydrostat

A

pressure compensator

96
Q

What can a bent axis pump withstand that an in-line cant

A

High vacuum at inlet

97
Q

Are gear pumps fixed or variable displacement

A

Fixed

98
Q

Which pump has a crescent seal type

A

Internal gear (inner gear has less teeth than outer as well)

99
Q

What does increasing swash plate angle do

A

Increase stroke

100
Q

Which piston pump has check valves in the pistons

A

Radial

101
Q

Rings used when no creep is tolerated in a cylinder

A

Synthetic

102
Q

What may be used on a cylinder with a long rod that magnifies side loads

A

Stop tubes

103
Q

Best port connections for hydraulic cylinders

A

ORB

NPTF if using tapered

104
Q

Should the cylinder ports be mounted on the top or bottom

A

Top

105
Q

Types of hydraulic motors

A

LSHT (low speed high torque)
HSLT (high speed low torque)
Limited rotation motors

106
Q

The amount of fluid required to turn the output shaft one revolution is called

A

Displacement

107
Q

The three types of internal gear motors

A

Direct drive
orbiting gear
roller vane

108
Q

Plumbing tube K, L, M thickness

A

K - thick
L - medium
M - thin

109
Q

A full vacuum hose is rated for this

A

28 inches of mercury

110
Q

Type of hose for pump inlet

A

Vacuum

111
Q

Recommended maximum velocities

A

Maximum pump inlet - 2 to 4 feet/second

Maximum pressure line - 7 to 20 feet/second

112
Q

Immediately recognized by a rattling sound and confirmed by abnormally low pressure at pump inlet

A

Cavitation

113
Q

What to use when regular hydraulic oil is not available

A

Automatic transmission fluid (ATF) or engine crankcase oil

114
Q

Hydraulic tanks are made from this

A

9 or 11 gauge steel

115
Q

Water coolers are also called this

A

Shell and tube heat exchanger

116
Q

Three types of reservoirs

A

Open
Pressurized (1 to 3 psi above atmosphere)
Closed-circuit (only 15% of flow back to tank)

117
Q

4 types of mounting styles for reservoirs

A

Flat top (power pack)
L shaped
Overhead stack
Vertical mount (compact, pump inside reservoir)

118
Q

Percentage of hydraulic component failure due to contamination

A

80%

119
Q

Micron sizes that do the most damage

A

14, 6, 4

120
Q

Metal to metal seal leakage percentage

A

5-15%

121
Q

Accumulator charge levels

A

Energy storage applications - 90% of minimum working pressure
Pulsation dampening -70% of normal working pressure
Shock absorption - 75% of normal working pressure
Never less than 25% of max system pressure

122
Q

Small lines and passages in valves are called this

A

Pilots

123
Q

What kind of relief valve is used in a system with an accumulator

A

Unloading

124
Q

Are pressure reducing valves normally open or normally closed

A

Normally open

125
Q

Difference between a sequence valve and a counterbalance

A

Counterbalance has an internal drain, sequence has an external drain

126
Q

Where are counterbalance valves located

A

The loaded end of the cylinder

127
Q

What do pilot chokes do on a DCV

A

Control shift speed of the spool

128
Q

Order of valves in a stack valve

A

Bottom - relief
Middle - flow
Top - directional

129
Q

This valve is also known as a high-low circuit

A

Unloading valve

130
Q

Bypass compensators only works for this kind of flow control

A

Meter-in (Restrictor compensators work for both meter in and meter out)

131
Q

The two automatic swash plate controls are

A

Pressure limiting compensator (limits maximum pressure in the system, saves energy)
Load sensing compensator (Can be used with pressure limiting compensator)

132
Q

Are radial piston pumps variable or fixed

A

Both (require large volumes)

133
Q

When do unbalanced vane pumps need springs to seal

A

Below 600rpm

134
Q

The two common causes of vane pump failure

A

Contamination, aeration/cavitation

135
Q

Used as a charge pump

A

Gerotor

136
Q

Most common industrial mount

A

Tie rod mount

137
Q

Motors that have been modified to turn only part of a revolution

A

Limited rotation motors

138
Q

Staffa is a type of what

A

Radial piston motor

Millwright Level 3 (5 decks)

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