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Millwright Level 3 > Compressors > Flashcards

Compressors Flashcards

1
Q

Screw compressors are typically used for what kinda pressures?

A

Lower pressure

100 - 175 Psig

25 - 8500 CFM

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2
Q

What makes the screw compressor economical, reliable and easy to maintain?

A

Limited number of moving parts

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3
Q

What are the two basic types of screw compressors?

A

Single rotor

Dual rotor

Either wet screw or dry screw

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4
Q

Which is more efficient, under compression or over compression?

A

Under compression

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5
Q

How does volumetric efficiency increase?

A

Typically with compressor speed.

The faster the rotors are turning the less time there is for the air to leak backward toward the suction

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6
Q

What determines compressor capacity?

A

Rotor length, diameter, lobe and flute design, and speed

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7
Q

What are the two lobe profiles in screw compressors?

A

Symmetrical

Asymmetrical - most commonly used

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8
Q

What is the purpose of the oil in a wet screw compressor?

A
  • Absorb most of the heat
  • seal the gaps between the rotors and casing to reduce leakage
  • lubricate bearings and gears
  • prevent metal to metal contact of the rotors
  • reduce noise
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9
Q

Are timing gears needed in wet compressors?

A

No because the oil lubrication allowing for the male rotor can directly drive the female rotor.

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10
Q

What are the two classifications of compressors?

A

Dynamic action: deliver large volumes at relatively low pressures

Positive displacement action: deliver moderate volumes of air at high pressure

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11
Q

What type of motion does a reciprocating compressor have?

A

Positive displacement action

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12
Q

What are the different types of positive displacement rotary compressors?

A

Vane, lobe, and screw compressors

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13
Q

Dynamic rotary compressors are?

A

Centrifugal compressors

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14
Q

What is the purpose of an unloading valve?

A

It can prevent further compression once the maximum is reached

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15
Q

What are other ways besides an unloading valve are there to control the maximum air pressure?

A

Throttling the air intake
Using a variable speed drive
Using a pressure switch

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16
Q

What are the types of reciprocating compressors?

A

Single acting or double acting

Single stage or multi stage

“Two stage double acting compressors give more compressed air per energy dollar than any other compressor

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17
Q

Rotary compressors are generally smaller then piston compressors and have less_________?

A

Vibration

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18
Q

Multi stage vane compressors require ____________ between the stages?

A

Intercoolers

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19
Q

How can you get dry air (no oil) with a vane compressor?

A

By using vanes with special wearing surfaces.

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20
Q

What does a lobe compressor do?

A

Deliver high volume air at low pressure

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21
Q

What is a 4+6 screw compressor for?
6+8 used for?
3+4 used for?

A

General use

6+8 = high pressure/low volume
3+4= low pressure/high volume

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22
Q

What is needed in dry screw compressor to prevent contact between the rotors?

A

Timing gears

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23
Q

Why don’t wet screw compressors need timing gears?

A

One rotor drives the other, and oil in between moving parts to seal and reduce wear

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24
Q

What is air slip?

How can it be reduced?

A

Air returning to the inlet side past the sealing surfaces in a screw compressor.

Air slip can be reduced by by running a higher RPM

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25
Q

How can you increase pressure with centrifugal type compressors?

A

Use a multi stage unit to increase working pressure

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26
Q

Why must air go through an inter cooler after it leaves the first stage of a multi stage compressor?

A

The air must be cooled before it goes to the next stage to reduce its volume.

27
Q

What are the different types of intercoolers?

A

Air

Or

Liquid cooled

28
Q

Symbols for water traps in compressor system

A
29
Q

Symbol for intercoolers in compressor system

A
30
Q

What is the purpose of an aftercooler?

A

Cools the air after it leaves the compressor and before it gets to the receiver.

31
Q

Symbol for air receivers

A
32
Q

What are the two main functions of a receiver tank?

A

Acts as a reservoir to accommodate any fluctuations

It reduces the velocity of the air allowing any moisture to settle out.

33
Q

What must a pressure tank have?

4 things

A

Safety relief valve

A drain valve

Fusible plug

Air pressure gauge

34
Q

What is the safety valve usually set for?

A

5-10percent about systems maximum pressure

35
Q

What are the two groups of industrial air?

A

Instrument air - must be clean, dry and free of oil

Plant air - should be clean and have low moisture and oil content

36
Q

Symbol for air dryer

A
37
Q

What is the purpose of an air dryer?

A

Remove water from compressed air. This reduces the dew point. They can lower the due point as low a -400degree C

38
Q

What are the different types of air dryers?

A

Deliquescent dryers

Regenerative desiccant dryer

Refrigeration dryer

Membrane dryer

39
Q

Symbol for air filter

A
40
Q

Symbol for pressure regulator.

A
41
Q

Symbol for air lubricators

A
42
Q

What are the two types of air lubricators and what are their purposes?

A

Fog lubricators - serve best when the flow to the component is straight and short

Mist lubricator - serves best when the oil mist be carried long distances, so that the oil will not settle in the line.

43
Q

FRL(filter, regulator, lubricator) symbol

A
44
Q

In a pneumatic system what do:
Pressure reducing valves (regulators) do?
Directional control valve (DCV) do?
Flow control valve do?

A

Regulators - reduce pressure at branch lines for its specific application

DCV’s - control the movement of the actuators

Flow control - control the volume (speed of actuator)

45
Q

Pneumatic DCV symbols

A
46
Q

When is a quick exhaust used?

A

When the cylinder is required to return quickly.

This allows the air to exhaust right at the cylinder instead of going back to the DCV exhaust

47
Q

Quick exhaust symbol

A
48
Q

When routing pneumatic lines what are the three most common systems?

A

Grid

Decentralized

Loop

49
Q

What pneumatic piping system is the simplest and cheapest?

A

Grid

Air systems at the end of the system may get starved of air

50
Q

Which pneumatic piping system uses multiple grids with their own compressors?

A

Decentralized

51
Q

Which is the preferred pneumatic piping system?

A

Loop system

52
Q

What are the eight major components of a reciprocating compressor?
Frame
Crankshaft
Connecting rod
Cross head and guides
Pistons
Cylinders
Distance pieces
____________

A

Valves

53
Q

What is the connecting rod attached to?

A

Crank shaft on one end and

Cross head on double acting cylinders

To the piston on single acting compressors

54
Q

What is the purpose of a cross head?

A

To keep the piston rod centred through the packing

55
Q

What does the piston do?

A

Compresses the gas in the cylinder

Can be single or double acting

56
Q

What is cylinder assembly include?

A

Inlet and outlet valve ports

Passages

Piping

57
Q

What is the purpose of the valves in the cylinder?

A

Control the flow of gas in and out of the cylinder

58
Q

How are compressor valves different from the valves on an engine?

A

Compressor valves open and close automatically due changes in pressure on either side of the valve.

59
Q

What are the different ways to unload a compressor?

A

Start/stop
Inlet valve unloading
Variable speed
Bypass
Variable volume pocket

60
Q

What can be an issue with an inlet valve unloading method?

A

Because the compressor continues to run it increases valve temperatures

61
Q

Intercoolers cool the air between stages. Doing this _________ the amount of power required to compress the gas.

A

Decreases

62
Q

What is the purpose of the aftercooler?

A

Remove moisture after the compression is complete

63
Q

What does FAD stand for?

A

Free air delivered

Millwright Level 3 (15 decks)

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