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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
How can you increase pressure with centrifugal type compressors?
Use a multi stage unit to increase working pressure
26
Why must air go through an inter cooler after it leaves the first stage of a multi stage compressor?
The air must be cooled before it goes to the next stage to reduce its volume.
27
What are the different types of intercoolers?
Air Or Liquid cooled
28
Symbols for water traps in compressor system
29
Symbol for intercoolers in compressor system
30
What is the purpose of an aftercooler?
Cools the air after it leaves the compressor and before it gets to the receiver.
31
Symbol for air receivers
32
What are the two main functions of a receiver tank?
Acts as a reservoir to accommodate any fluctuations It reduces the velocity of the air allowing any moisture to settle out.
33
What must a pressure tank have? 4 things
Safety relief valve A drain valve Fusible plug Air pressure gauge
34
What is the safety valve usually set for?
5-10percent about systems maximum pressure
35
What are the two groups of industrial air?
Instrument air - must be clean, dry and free of oil Plant air - should be clean and have low moisture and oil content
36
Symbol for air dryer
37
What is the purpose of an air dryer?
Remove water from compressed air. This reduces the dew point. They can lower the due point as low a -400degree C
38
What are the different types of air dryers?
Deliquescent dryers Regenerative desiccant dryer Refrigeration dryer Membrane dryer
39
Symbol for air filter
40
Symbol for pressure regulator.
41
Symbol for air lubricators
42
What are the two types of air lubricators and what are their purposes?
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
FRL(filter, regulator, lubricator) symbol
44
In a pneumatic system what do: Pressure reducing valves (regulators) do? Directional control valve (DCV) do? Flow control valve do?
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
Pneumatic DCV symbols
46
When is a quick exhaust used?
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
Quick exhaust symbol
48
When routing pneumatic lines what are the three most common systems?
Grid Decentralized Loop
49
What pneumatic piping system is the simplest and cheapest?
Grid Air systems at the end of the system may get starved of air
50
Which pneumatic piping system uses multiple grids with their own compressors?
Decentralized
51
Which is the preferred pneumatic piping system?
Loop system
52
What are the eight major components of a reciprocating compressor? Frame Crankshaft Connecting rod Cross head and guides Pistons Cylinders Distance pieces ____________
Valves
53
What is the connecting rod attached to?
Crank shaft on one end and Cross head on double acting cylinders To the piston on single acting compressors
54
What is the purpose of a cross head?
To keep the piston rod centred through the packing
55
What does the piston do?
Compresses the gas in the cylinder Can be single or double acting
56
What is cylinder assembly include?
Inlet and outlet valve ports Passages Piping
57
What is the purpose of the valves in the cylinder?
Control the flow of gas in and out of the cylinder
58
How are compressor valves different from the valves on an engine?
Compressor valves open and close automatically due changes in pressure on either side of the valve.
59
What are the different ways to unload a compressor?
Start/stop Inlet valve unloading Variable speed Bypass Variable volume pocket
60
What can be an issue with an inlet valve unloading method?
Because the compressor continues to run it increases valve temperatures
61
Intercoolers cool the air between stages. Doing this _________ the amount of power required to compress the gas.
Decreases
62
What is the purpose of the aftercooler?
Remove moisture after the compression is complete
63
What does FAD stand for?
Free air delivered

Millwright Level 3 (15 decks)

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