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3rd Year Millwright > Compressors > Flashcards

Compressors Flashcards

1
Q

what is a positive displacement compressor?

A

Where the inlet and the discharge are positively sealed from each other

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2
Q

what is a nonpositive displacement compressor?

A

The rely on airflow through the compressor to separate high-pressure from low pressure

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3
Q

What is gauge pressure?

A

Absolute pressure -14.7 psi

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4
Q

what is absolute pressure?

A

Gauge pressure +14.7 psi

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5
Q

what is atmospheric pressure?

A

14.7 psi

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6
Q

What are the four main properties of gas under pressure?

A

-gas can be compressed
-Gas will take the shape of a container
-Gas will flow from high-pressure to low pressure
-Gas will fill the complete container

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7
Q

what two ways can the pressure of a gas be increased?

A

Reducing the size of the container
Heating the gas

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8
Q

what are two examples of rotary compressors that are considered as being nonpositive displacement?

A

Radial flow
Axial flow

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9
Q

how is a compressor capacity specified?

A

Volume/CFM

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10
Q

what are four examples of rotary compressors that are considered positive displacement?

A

sliding vein
Screw (helical)
Liquid ring (piston)
Straight lobe

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11
Q

what is a single stage compressor?

A

It compresses the air from the inlet to the final discharge pressure in one stroke

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12
Q

What is a multi stage compressor?

A

More than one stroke or cycle of compression is needed to go from inlet pressure to final discharge pressure

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13
Q

List five examples of a compressors prime mover

A

Motors
Engines
Turbines
Gas
Steam

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14
Q

What is the purpose of using intercoolers between stages?

A

It removes the heat generated by compression between stages

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15
Q

Where is the aftercooler located, and what is the purpose of using after coolers?

A

It’s located after the discharge, and it removes heat from the compressed, gas after the final stage, and condenses out the moisture

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16
Q

what are the manufacturers of air receiver supposed to incorporate into the design of an air receiver?

A

Pressure safety valves
Gauge
Drain

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17
Q

What styles of air filters may you find on a positive displacement compressor?

A

dry filters
Labyrinth
Oil bath

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18
Q

In a sliding vein, compressor, explain the position of the rotor, which enables it to compress air

A

The rotor is offset, the veins go around the crescent shape, which compresses the gas, and allows it to escape through a small opening at the discharge port

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19
Q

what keeps the veins in contact with the housing?

A

Centrifugal force

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20
Q

is lubrication critical in the operation of a sliding vein compressor?

A

The metal veins must be lubricated, the synthetic ones must not be

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21
Q

Why must the rotor slot clearance be checked periodically?

A

Slot where it can cause the veins to wear or break

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22
Q

what two methods are commonly used to cool vein compressors?

A

Water jacket
Air cooled

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23
Q

what four methods may be used for unloading vein compressors

A

Start stop
Vent the external bypass
Block the inlet
Very the speed

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24
Q

what family of compressors does a liquid ring compressor fall into?

A

Positive displacement – rotary

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25
Q

what is the purpose of the liquid in a liquid ring compressor?

A

To provide oil free air

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26
Q

what are the two main designs of the liquid ring compressor?

A

Concentric– balanced
Eccentric – unbalanced

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27
Q

is the liquid ring compressor oil free?

A

Yes

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28
Q

What two functions can the liquid ring compressor perform?

A

supply oil free air
Cooling of the air

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29
Q

explain the difference between the dry screw (timed) and the wet screw

A

The dry screw does not need lubrication because it has timing gears and the screw uses injected oil to seal and cool the gas during compression

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30
Q

which type of screw compressor requires timing gears

A

Dry screw

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31
Q

which combination of male/female lobe construction is most common?

A

6 flute female, 4 lobe male

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32
Q

what three purposes does the lube, oil and a wet screw compressor have?

A

seals internal clearances
Cools gas during compression
Lubricates the rotors

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33
Q

What methods are used to unload a screw compressor?

A

intake throttling
Slide valve
Variable speed
Stop/start

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34
Q

What family of compressors does the lobes style compressor fall into?

A

Positive displacement – rotary

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35
Q

what two uses does the lobes style compressor have?

A

It can create pressure and vacuum

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36
Q

does the lobes style compressor have a built-in pressure ratio?

A

No, because there’s no reduction in volume

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37
Q

T or F

A lob style compressor does not require timing gears

A

False

38
Q

what are the two types of dynamic compressors?

A

Radial/centrifugal
Axial flow

39
Q

on a centrifugal compressor, what stationary device is used to redirect flow and slow the velocity of the air or gas

A

Stationary diffuser

40
Q

what are the shaft speeds for dynamic compressors as compared to reciprocating compressors?

A

Very high 20,000 to 100,000 RPM

41
Q

can centrifugal compressors be designed as single or multi stage?

A

Both, but they’re usually single stage

42
Q

can axial flow compressors be designed as single stage or multi stage?

A

They are multi stage only

43
Q

what two designs of casting are used on centrifugal compressors?

A

horizontal split – multi stage
Vertical split – higher pressures, better sealing

44
Q

What styles of bearings are used on centrifugal compressors?

A

Plain bearings

45
Q

what direction is the gas flow in axial flow compressors?

A

Parallel to the shaft axis

46
Q

explain the configuration of the rotor in an axial flow compressor

A

tapered drum:
Small end long blades at the inlet, and large end short blades at the discharge

47
Q

Which direction is the thrust in an axial flow compressor, and what method is used to control it?

A

Discharge to inlet, use a thrust, bearing and a balance piston

48
Q

what methods of adjustment are used on axial flow compressors, to vary the output flow?

A

Adjustable stater blades
Restrict the inlet

49
Q

what is compressor surge?

A

Too low of a pressure

50
Q

what do the term stonewalling or choking refer to?

A

Airflow is too high

51
Q

What is the effect of blow by on compressor performance?

A

Reduced efficiency

52
Q

what is the purpose of wear bands?

A

To support the piston so there is no contact on the cylinder

53
Q

if all four-cylinder compressor, discharges into a common line, how many stages does it have?

A

1

54
Q

what is the most common way to control the output volume of a large reciprocating compressor?

A

-Opening or closing clearance pockets
-Control suction valves from discharge pressure

55
Q

How does piston and clearance affect, output pressure or output volume?

A

More end clearance = less output volume
It does not affect pressure

56
Q

Why is it important to install dry liners to the specified fit?

A

For proper heat transfer

57
Q

what are three ways to set piston end clearance?

A

Count the threads in the crosshead
Trammel
Lead wire crush or feeler gauges

58
Q

what is the quickest way to check rod bearing clearances?

A

Bump or lift check

59
Q

which is the greatest force on the rod of a double acting compressor the tension or the compression?

A

Compression

60
Q

is rod load affected by the inlet or the discharge pressure?

A

Both

61
Q

on a single stage compressor is the discharge pressure achieved on one stroke or more than one

A

one stroke

62
Q

what component in a compressor requires the most maintenance?

A

Valves

63
Q

what are two of the best methods for unloading a large compressor?

A

Clearance pockets
Inlet unloading

64
Q

what is the purpose of a crosshead?

A

keeps the piston in line with the centreline of the cylinder

65
Q

what are two reasons for an intercooler

A

Increases efficiency
Reduces temperature between stages

66
Q

How was piston and clearance calculated

A

2/3 at the head end and 1/3 at the rod end

67
Q

does an exhaust valve that is bypassing run hotter or colder?

A

Hotter

68
Q

What effect does valve lift have on the performance of a compressor?

A

increased lift = increase flow rate

69
Q

do packing rings match marks, face towards the pressure or away from the pressure?

A

Towards

70
Q

which type of rings require the deepest cup a metallic ring or a Teflon ring?

A

Teflon

71
Q

where is the wiper packing located?

A

In the frame

72
Q

Where is the aftercooler located?

A

Between the last stage and the receiver

73
Q

can absorption material be reused?

A

No

74
Q

What are three advantages of a refrigerant dryer?

A

no chemicals
Continuous operation
Automatic

75
Q

what type of material can be regenerated?

A

adsorption

76
Q

what are two definitions of dewpoint?

A

-Temperature at which water vapour saturates a gas
-Temperature at which water vapour condenses from a gas

77
Q

is dewpoint affected by temperature?

A

No, it is a temperature change

78
Q

is dewpoint affected by pressure?

A

yes, increase pressure raises dewpoint

79
Q

if the pressure of a gas drops, will the dewpoint increase or decrease?

A

Decrease

80
Q

which type of dryer can achieve the lowest dewpoint

A

adsorption

81
Q

can receiver, air pressure be used to operate intake unloaders?

A

yes

82
Q

what type of compressor is used mainly for high-volume but low pressure?

A

Axial flow
Lobe compressor

83
Q

What does Rod runout indicate?

A

Worn wear bands and cylinder
Worn crosshead shoes

84
Q

why is airline diameter important?

A

it should be large enough to minimize pressure drop

85
Q

do dynamic compressors need to receiver?

A

no

86
Q

are dynamic compressors mainly used for high volume or low volume?

A

High volume

87
Q

What type of screw compressors would be the best for oil free air?

A

Dry screw

88
Q

What are the two different rod loads?

A

compression
Tension

89
Q

What is the purpose of a dummy piston on a compressor?

A

Dynamic balance

90
Q

What happens when a ruptured disc ruptures on a distribution block?

A

It can shut down the compressor automatically

91
Q

What does a distribution block system do?

A

Make sure a set amount of oil gets into each lube point regardless of pressure

3rd Year Millwright (21 decks)

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