Module D

Question 1

What are the two main categories of screw compressors?

Answer 1

Helical lobe or screw compressors fall into two main categories:
1. Oil-flooded (wet)
2. Oil free (dry)
they may be single-stage or multi-stage, depending on the requirements

Question 2

Which rotor is the driver in a screw compressor?

Answer 2

The male rotor is usually the rotor that is directly driven

Question 3

What 4 factors determine the capacity of a screw compressor?

Answer 3

• Rotor length
• diameter
• lobe/flute design
• speed

Question 4

What determines the discharge pressure of a screw compressor?

Answer 4

• The location of the inlet port along the length of the rotor
• The length of the path along the lobes and flutes
• The discharge port

Question 5

What function does the oil in an oil-flooded screw compressor serve?

Answer 5

• It dissipates some of the heat due to compression
• Seals gaps between the rotors and the casing to prevent leakage
• Lubricates the bearings and gearbox
• Reduces noise level

Question 6

Which is the simplest type of control system for screw compressors?

Answer 6

Online/off-line control

Question 7

Which control system allows the compressor to produce only the amount of air required by the system?

Answer 7

Modulation control

Question 8

What must be included to prevent rotor contact in a dry screw compressor?

Answer 8

Timing gears must be used to prevent rotor contact in dry screw compressors

Question 9

Where are the thrust bearings located on the screw compressor?

Answer 9

At the discharge end

Question 10

Air filters should be able to remove particles down to what size before the air enters the compressor?

Answer 10

5 Microns

Question 11

What functions do oil separators perform?

Answer 11

1. Separate oil from the air
2. act as an oil reservoir
3. act as an air receiver

Question 12

What two functions does the minimum pressure valve perform?

Answer 12

1. Maintains air pressure in the separator
2. acts as a check valve, preventing flow reversal

Question 13

What is the function of the thermal mixing valve?

Answer 13

Maintain a minimum oil injection temperature

Question 14

What should be done first before putting a compressor back into service after an overhaul or motor change?

Answer 14

Check for correct rotation after motor or air unit replacement

Question 15

True or false: Lobe blowers are used to produce high pressure and low volumes

Answer 15

False

Question 16

What is the advantage of the helical lobe blower over the two lobe blower?

Answer 16

Increased pressure and smoother air delivery

Question 17

True or false: Only helical lobe blowers require timing gears.

Answer 17

False

Question 18

List the 6 types of bearings that are found on lobe blowers?

Answer 18

• Single row ball bearings
• double row ball bearings
• deep groove ball bearing
• spherical roller
• cylindrical roller
• angular contact bearings

Question 19

What should be determined before resetting the timing on a lobe blower?

Answer 19

Before attempting to retime and set lobe clearance, determine whether the unit is unidirectional or bi-directional rotation and always refer to manufacture’s specifications

Question 20

What should be done before starting a blower after an overhaul?

Answer 20

Before starting the blower, turn it over by hand to ensure that it rotates freely in the direction of rotation

Question 21

Care should be taken to prevent what from happening while you are attempting to set the lobe clearance in a blower?

Answer 21

Take care to prevent injury to the fingers or hands caused by pinching from the gears