Book 2 Chapter 27: Air Compression

Question 1

A reciprocating compressor is one in which:
A) Vanes are fitted into radial slots
B) There are two intermeshing screws
C) Air is compressed by a piston moving back and forth within a piston
D) Air is increased in velocity and the velocity is converted to pressure

Answer 1

C) Air is compressed by a piston moving back and forth within a piston

Question 2

Centrifugal compressors:
A) Are commonly used for large volume, low pressure applications
B) Rotate at very low speeds
C) Are classified as positive displacement compressors
D) Require suction and discharge valves

Answer 2

A) Are commonly used for large volume, low pressure applications

Question 3

Air compressor receivers:
A) Are used to cool the air
B) Must conform to ASME Code, Section VI
C) Allow moisture and oil to be removed from the air
D) Are always connected to the suction of the compressor

Answer 3

C) Allow moisture and oil to be removed from the air

Question 4

Adsorbents and absorbents:
A) Are the same thing but spelled differently
B) Are two different classes of sorbents
C) Both have water collected on their surface
D) Are used to cool the air

Answer 4

B) Are two different classes of sorbents

Question 5

Lubricating oil is necessary in an air compressor to perform which of the following functions?
A) Reduce friction and resulting power loss by providing a film between surfaces
B) Remove heat produced by friction
C) Reduce corrosion by providing a coating for metal surfaces
D) All of the above

Answer 5

D) All of the above

Question 6

Which of the following types of air compressors requires internal lubrication?
A) Rotary screw
B) Rotary lobe
C) Axial
D) Centrifugal
E) None of the above

Answer 6

E) None of the above

Question 7

Compressor lubrication oil provides:
1. Corrosion resistance
2. Sealing around pistons, vanes, etc
3. Heat removal
4. Wear prevention

A) 1,2,4
B) 1,2,3,4
C) 2,4
D) 1,3,4
E) 2,3,4

Answer 7

B) 1,2,3,4

Question 8

The compressor that would favour volume over pressure would be the:
A) Rotary lobe
B) Axial
C) Centrifugal
D) Sliding vane
E) Screw

Answer 8

C) Centrifugal

Question 9

Which of the following is not a true advantage of sliding vane compressors over reciprocating compressors?
A) They are more efficient
B) They require less power when starting up
C) Their initial cost is less
D) They do not require inlet or discharge valves
E) They produce a steadier flow of air

Answer 9

A) They are more efficient

Question 10

Compressor internal lubrication apples lubrication to:
A) Connecting rod bearings
B) Pistons and cylinder walls
C) Crankshaft bearings
D) Rotor shaft bearings
E) Crossheads

Answer 10

B) Pistons and cylinder walls

Question 11

An advantage of dynamic compressors is that they do not require:
A) Air receivers
B) Inlet baffles
C) Maintenance
D) Internal lubrication
E) External lubrication

Answer 11

D) Internal lubrication

Question 12

To reduce air temperature between stages, we would use:
A) A chiller
B) An intercooler
C) An aftercooler
D) A receiver
E) A converter

Answer 12

B) An intercooler

Question 13

In a centrifugal compressor, the kinetic energy is converted to potential energy in the:
A) Volute, diffuser or both
B) Compressor cavity
C) Volute only
D) Diffuser only
E) Intercooler

Answer 13

A) Volute, diffuser or both

Question 14

A constant speed compressor is controlled by a/an:
A) VFD (Variable Frequency Device)
B) Unloader
C) Fluid coupling
D) Variac (Variable auto transformer)
E) Variable speed coupling

Answer 14

B) Unloader

Question 15

A reciprocating compressor unloader:
A) Uses a waste gate
B) Holds intake valves open
C) Throttles discharge
D) Throttles suction
E) Uses variable inlet vanes

Answer 15

B) Holds intake valves open

Question 16

In double-acting type of reciprocating compressor:
A) Compression and discharge take place at one end of the cylinder only
B) Compression takes place after discharge
C) Compression takes place at one end and discharge at the other
D) Compression and discharge take place at both ends of the cylinder
E) There is one compression strokes per revolution of the crankshaft

Answer 16

D) Compression and discharge take place at both ends of the cylinder

Question 17

Dynamic compressors accelerate the air using impellers or blades and convert the:
A) Kinetic energy of the high velocity, high pressure air into the potential energy of low velocity, high pressure air
B) Kinetic energy of the high velocity, low pressure air into the potential energy of low velocity, high pressure air
C) Kinetic energy of the high velocity, high pressure air into the potential energy of low velocity, high pressure air
D) Kinetic energy of the high velocity, low pressure air into the potential energy of low velocity, low pressure air
E) Kinetic energy of the low velocity, low pressure air into the potential energy of low velocity, high pressure air

Answer 17

B) Kinetic energy of the high velocity, low pressure air into the potential energy of low velocity, high pressure air

Question 18

One of the most common designs of a rotary compressor is the ________ type.
A) Axial flow
B) Centrifugal
C) Turbine
D) Sliding vane
E) Positive displacement

Answer 18

D) Sliding vane

Question 19

The sliding vane compressor operates at speeds of up to:
A) 2000 r/min
B) 5000 r/min
C) 4000 r/min
D) 3000 r/min
E) 1000 r/min

Answer 19

D) 3000 r/min

Question 20

The temperature very exceptional circumstances may be about _______ neat the end of the compression stroke.
A) 175ºC (347ºF)
B) 225ºC (437ºF)
C) 150ºC (302ºF)
D) 90ºC (194ºF)
E) 75ºC (167ºF)

Answer 20

B) 225ºC (437ºF)

Question 21

A piston rod in a double-acting compressor has:
A) Linear travel at one end and angular at the other
B) Angular travel at one end only
C) Linear travel at both ends
D) Angular travel at both ends
E) Linear travel at one end only

Answer 21

C) Linear travel at both ends

Question 22

A single-stage centrifugal compressor is one with a single impeller and may be able to compress atmospheric air to a pressure of about:
A) 100kPa (14.5psi)
B) 300kPa (43.5psi)
C) 500kPa (72.5psi)
D) 200kPa (29psi)
E) 600kPa (87psi)

Answer 22

B) 300kPa (43.5psi)

Question 23

An air receiver is a pressure vessel their specifications must conform to the:
A) ASME Code, Section IV
B) ASME Code, Section VIII
C) ASME Code, Section I
D) ASME Code, Section III
E) ASME Code, Section VI

Answer 23

B) ASME Code, Section VIII

Question 24

Which of the following statements about centrifugal compressor advantages is incorrect?
A) They are commonly used for low pressure applications
B) They are of simple and rugged construction
C) They have low maintenance requirements
D) They are commonly used for large volume applications
E) Their efficiency is higher than the positive displacement type

Answer 24

E) Their efficiency is higher than the positive displacement type

Question 25

Air driers may use adsorbents like Silica-gel that is very porous and has an extremely large surface it is able to hold a large amount of moisture up to _______ of its own weight.
A) 40%
B) 60%
C) 50%
D) 20%
E) 30%

Answer 25

A) 40%