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Third Millwright > Hydraulics Part 2 pumps and actuators > Flashcards

Hydraulics Part 2 pumps and actuators Flashcards

1
Q

Describe a dynamic pump

A

There is no positive seal between the inlet and discharge

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2
Q

Why must hydraulics use positive displacement pumps?

A

Because pressure must remain in the downstream lines

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3
Q

What are the three types of positive displacement pumps?

A

They are classified the name of the part that does the pumping
Piston
Vane
Gear

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4
Q

What three ways can the output be changed in a hydraulic pump?

A

Use a flow control and relief valve
Change the speed of the driver
Use a variable displacement pump

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5
Q

What are the different types of piston pumps?

A

In line axial piston, bent axis piston,rotary piston, radial piston

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6
Q

What are the two types of pumps?

A

Positive displacement, and non positive displacement, which is also known as dynamic

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7
Q

What is the name of the device that tilts and varies output in an inline axial piston pump?

A

Swash plate

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8
Q

What are the names of the two Pistons that regulate the pressure limiting swash plate

A

The top one (smaller one) is called the bias piston, and the other is called a compensator control piston

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9
Q

What Are the three ways for controlling speed?

A

Conventional, pressure compensated, load sensing pressure compensated

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10
Q

What must you do when installing a load sensing pump?

A

It must be set with 200-400 psi standby pressure

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11
Q

Why should you monitor fluid viscosity in a system?

A

A decrease in fluid viscosity can lead to an increase in internal leakage

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12
Q

How is the bent axis piston pump different from the inline axial pump?

A

The angle is what determines displacement. There is no swash plate, the angle of the cylinder block determines it

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13
Q

What are some benefits of the bent axis piston pump?

A

It is the most rugged design, it can withstand high vacuum at the inlet, so it can be mounted above the fluid level in the reservoir

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14
Q

What are some maintenance tips for piston pumps?

A

Always prime the pump, ensure the case is full before startup, always connect case drain, maintain fluid cleanliness

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15
Q

Describe how a rotary piston pump works

A

Fluid is ported in and out through the centre, while the cylinder block rotates around it

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16
Q

What is the centre area of a rotary piston pump called?

A

Pintle

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17
Q

What do the Pistons ride on in a Rotary piston pump?

A

A retaining ring, or reaction ring

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18
Q

How is displacement changed on a rotary piston pump?

A

By moving the reaction ring because the pintle is fixed in the middle

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19
Q

How does a radial piston pump work

A

The cylinder is stationary and the center cam is eccentric and rotates

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20
Q

How does a vane pump rotate?

A

It has a splined rotor fitted with sliding vanes

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21
Q

What are the two types of vane pumps

A

Balanced and unbalanced

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22
Q

What does the vanes ride on

A

The Cam ring

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23
Q

Describe the inlet and outlet ports on an unbalanced vane pump

A

There is one on each side 180° apart

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24
Q

What is an advantage and a disadvantage of the unbalanced vane pump

A

And advantages it has a movable cam ring which allows for variable displacement. Disadvantage is it requires large bearings and casing to support the unbalanced load

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25
Q

What two ways are the vanes held against the cam ring?

A

Centrifugal force, and hydraulic pressure at the root of the vanes

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26
Q

Why is the balanced vane pump much more compact?

A

It has two pumping chambers that are 180° apart so the forces at one outlet act against the forces on the opposing outlet

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27
Q

If the balanced vane pump rotor is centered how does it create pockets?

A

It uses an elliptical cam

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28
Q

What is the name of the cutout on the root of the vane?

A

Intra vane

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29
Q

What are some benefits of the Intra vane?

A

More stable, less noise, less maintenance

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30
Q

What are the two types of gear pumps?

A

Internal gear and external gear

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31
Q

How is the pumping action created in an external gear pump?

A

The meshing of the two gears creates the pumping action

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32
Q

How is gear pump displacement adjusted?

A

It is not adjustable without a fluid bypass. You must adust the rpm of the prime mover

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33
Q

Why are radial loads high on gear pumps?

A

Because of the highly unbalanced hydraulic pressures from the inlet to discharge side. Therefore they use heavy needle bearings or bushings to support those loads

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34
Q

What are the two types of internal gear pumps?

A

The crescent seal type, and the gerotor type

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35
Q

What is the purpose of the crescent seal on the internal gear pump?

A

It creates the positive seal between the inlet and discharge

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36
Q

Describe the gerotor internal gear pump

A

It’s used mainly as a charge pump, has a star shaped rotor with one less tooth than the lobes on the outer gear

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37
Q

Describe the difference between single acting and double-acting cylinders

A

Single acting only exert force in one direction, double acting is both ways

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38
Q

Describe the characteristics of a telescopic cylinder

A

It is a series of sleeves nested together, provides a long stroke but very compact when retracted. As it extends the speed increases and force decreases due to the diminishing diameter of each sleeve

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39
Q

Describe a differential cylinder

A

Has the cap end on one side, and rod end on the other. More force is created on the cap end due to the larger area.

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40
Q

What is a double rod cylinder?

A

It is a non-differential cylinder so it produces equal force in speed in both directions. It can push and pull simultaneously

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41
Q

What is The difference between the rod seal and the rod wiper?

A

The rod seal keeps the fluid inside the piston, and the rod wiper keeps contaminants out

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42
Q

What is the purpose of the tandem cylinder

A

It is used for very high force and short stroke requirements

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43
Q

Describe cylinder cushion

A

When the plunger comes to the end it plugs off the flow of fluid which is then forced to go through a small controlled opening that is adjustable similar to a meter out flow control

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44
Q

What is the purpose of the cylinder cushion

A

It is used to prevent mechanical shock

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45
Q

What is the purpose of a stop tube

A

It is a metal collar that fits over the piston rod next to the piston it is used to reduce sideloading on longer rods

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46
Q

What is the two types of Rod supports and what is their function

A

Center support, and tie rod support. They are used to provide rigidity for long stroke cylinders

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47
Q

What is the most recommended port, and what kind of threads does it have

A

The O-ring boss or orb for short is the most recommended. It has a straight thread and then O-ring seal and seat

48
Q

Where should you mount the bleed ports on a cylinder

A

You should try to mount the ports on top which allows any air trapped in the system to rise and escape through the port

49
Q

Why should you check for hot spots on the cylinder?

A

Because it is an indicator of internal leaking of the piston rings

50
Q

What is a hydraulic motors purpose

A

It converts fluid power into rotary motion

51
Q

There are three types of motors what are they?

A

Low-speed, high torque (LSHT) for smooth operation under heavy loads
High-speed, low torque(HSLT) for operating continuously at constant high speeds
Limited rotation motors-used in some robotics

52
Q

Describe the limited rotation motor symbol

A

It’s a half circle with two arrows pointing up

53
Q

How is displacement measured

A

Measured in cubic inches per revolution.

54
Q

Describe torque

A

It is the rotational force of the motor. It is expressed in foot-pounds

55
Q

What three things does torque depend on?

A

Inlet pressure
Surface area
Radius of rotation

56
Q

When you gain torque, what do you lose

A

Lose speed, and vice versa

57
Q

What does motor speed depend on?

A

Flow rate, volume

58
Q

What are the three types of internal gear motors

A

Direct drive gear motors
Orbiting gear Motors
Roller vane gerotors

59
Q

How is a sliding vane motor different from a vane pump?

A

The vane motor has springs under it, to make contact with the cam, as it starts too slow to use centrifugal force

60
Q

The axial piston motor adjusts torque with the swash plate how?

A

At maximum angle it has low speed, high torque, and minimum angle provides maximum speed, low torque

61
Q

Describe the radial piston motor

A

It is used in severe service, it’s a low-speed high torque motor. It is known as a Staffa

62
Q

What 5 things does hydraulic fluid do?

A

Lubricates, seals, energy transfer, heat transfer, Flushing contaminants

63
Q

What other considerations must be taken with hydraulic fluid

A

It must be compatible, resist foaming, be fire resistant, and have a high viscosity index

64
Q

Describe viscosity index

A

The ability for oil to maintain its properties over a range of temperature

65
Q

What is the relativity between control and compressibility of fluids?

A

If the fluid is less compressible, it gives more accurate control. Some systems will use a more compressible oil, to act as a shock absorber

66
Q

What are some characteristics of petroleum based fluids

A

They have a high viscosity index, are low cost and have low toxicity

67
Q

Give some characteristics of water-based fluids

A

There more expensive than petroleum based, they’re heavier than petroleum based, they oxidize faster, and the absorb water readily

68
Q

Give some characteristics of synthetic fluids

A

They are much more expensive, they have a high resistance to oxidation, a very high viscosity index, and increased life. Most synthetic fluid’s require special seal and hose material

69
Q

What is the most prominent type of vegetable oil used

A

Soy oil

70
Q

What are the main functions of the reservoir tanks

A

The reservoir tank is to hold a supply of fluid. It also warms or cools the fluid as needed, de-aerates the fluid, allows contaminants to settle out, reduces turbulence, and acts as a platform for the pumps and valves

71
Q

What does the air filter on a reservoir filter down to?

A

3 µm

72
Q

How is the tank made?

A

It is pickled and oiled (soaked in oil)

73
Q

How big is the reservoir for an open circuit tank?

A

2 to 3 times the pump output

74
Q

What is the purpose of the baffle

A

The barrier to direct flow from the return line away from the pump inlet. It prevents turbulence, promote cooling, promote settling, allows air to escape

75
Q

How is the return line directed in the tank

A

Return flow was directed outward towards the tank wall away from the pump inlet

76
Q

What is the inlet filter purpose

A

It filters down to about 100 µm. It’s purpose is to remove large contaminants that could cause Pump failure

77
Q

When you see a hydraulic symbol with arrows pointing in or out what does it mean

A

Arrows pointing in means heat is moving in (heater)and arrows pointing out the heat is leaving(cooling)

78
Q

What are the three types of reservoirs

A

Open, pressurized, closed circuit

79
Q

Describe a pressurized reservoir

A

The supply of low pressure regulated air is pumped into the tank approximately 1 to 3 PSI above atmosphere. You use these when airborne contamination is too great for the breather, or atmospheric pressure is not adequate to push fluid into the pump. It also can solve cavitation problems

80
Q

Describe a closed circuit reservoir

A

Most of the return flow goes directly back to the pump from the actuator. The reservoir holds approximately three quarters of the charge pump output

81
Q

What are the four main reservoir mounts

A

Flat top, L-shaped, overhead stack, vertical mount

82
Q

Describe the vertical reservoir mount

A

It is the most compact design, it increases cooling because the pump is immersed in the fluid, the pump system stays cleaner, less noise and sideloading and a positive suction head

83
Q

What are the four common sources of contamination of oil

A

New Oil, built-in, ingressed, generated

Ingressed=taken into system through leaky seals, dirty piston rods
Generated=wearing parts

84
Q

How do you prevent fine filters from getting clogged too quickly?

A

Install a coarse filter before to trap the bulk of the contaminants

85
Q

Why should you never use galvanized fittings in the hydraulic system

A

The zinc flakes off and gets in the system and reacts with the fluid

86
Q

What is the best way to get away from thread debris

A

Use O ring boss fittings

87
Q

What is iso range code?

A

A way to describe three different particle size levels in a sample
Eg 15/9/8

88
Q

What is the particle sizes we measure for?

A

2, 5, 15 µm

89
Q

What size microns do the most damage in the system

A

14,6, 4 micron particle sizes

90
Q

What is the difference between a strainer and a filter

A

A strainer is usually a wire mash with pore sizes larger than 50 µm. It is used at the pump inlet another feature is that you can wash it and reuse it

91
Q

What components does a filter consist of

A

Metal case containing filter element, a bypass valve, a bypass indicator

92
Q

What are the two types of filter elements

A

Pleaded fiberglass cloth supported by metallic mesh, or depth type media.

93
Q

How does depth type media work?

A

It does not have a constant pore size, it captures dirt by forcing the flow through a torturous where the good becomes trapped these filters are not washable and must be discarded after use

94
Q

Why is fiberglass superior to paper as a filter?

A

The glass fibers can be produced much more finely, they can be laid uniformly, they resist chemical action of the fluid

95
Q

At what colour indicator should you change the hydraulic filter?

A

As soon as the indicator turns yellow. This minimizes the amount of unfiltered oil through the system

96
Q

What must the strainer equipped with

A

A bypass to ensure full flow to the pump when the strainer clogs

97
Q

Where should pressure line filters be located?

A

Before any contaminant intolerant device such as servo, proportional, instrumentation

98
Q

How much slow should be through the return line filter to control contamination in the entire system

A

20% of the total system volume should pass through the filter per minute

99
Q

What are some of the requirements of the return line filter

A

Must be able to handle the maximum return line flow with minimum pressure drop. Must be a full flow filter however I return line filter is equipped with the bypass valve that is preset to divert flow

100
Q

What is the advantage of an off-line filter

A

Free of pressure pulsations, can be located where it is convenient to service

101
Q

When must you use an off-line filter system

A

When you use a pressure compensated variable displacement pump that is running at standby for extended periods

102
Q

When you see a brown sticky substance on a valve what is it

A

Gum and varnish

103
Q

Explain the beta ratio and filter efficiency

A

It is how many contaminants does it take until one passes through. For example a beta ratio of 10 means for every 10 particles one will go through for a 90% efficiency
A beta reading of 20 means for every 20 particles that get filtered one gets through for a 95% efficiency

104
Q

What methods can be used to remove water from a system

A

Drain it out of the hydraulic reservoir, coalescent filters, centrifuge, absorbent filters, desiccant air breathers

105
Q

What is the main cause of oxidation

A

Heat. For every 10°C you increase the temperature of the petroleum based fluid above 60°C the oxidation rate doubles

106
Q

When O-rings are used as stationary seals how much of their diameter must project above the groove?

A

10%

107
Q

What is the purpose of an accumulator

A

It gives the supplementary flow when demand needs it

108
Q

What kind of air is put into an accumulator

A

Nitrogen

109
Q

Accumulator precharge varies with applications define them

A

For energy Storage applications pre-charged to 90%
For pulsation dampening applications precharge to 70%
For shock absorption applications precharge to 75%

110
Q

What is another name for the swashplate

A

Yolk

111
Q

What instruments are required to check the system

A

Flow meter, pressure gauge, thermometer, tachometer

112
Q

What is the mechanism that protects the pressure gauge called

A

Snubber

113
Q

What is another name for a pipe or tube?

A

The fluid conductor

114
Q

How was all tubing and hoses measured?

A

OD

115
Q

What happens when the ID of tubing is decreased

A

The velocity decreases

Third Millwright (12 decks)

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