Screw Compressors/Lobe Blowers

Question 1

Rotary positive displacement compressor

Answer 1

-

Question 2

Dual rotor

Answer 2

• dry screw is oil free. Some incorporate a water spray within the compression chamber to cool and help seal - the air created can be reused
• wet screw is oil flooded by injected oil to lubricate the seal and cool the air end

Question 3

Compression cycle

Answer 3

• the male rotor has lobes that mesh with the flutes on the female rotor as they both rotate inside the housing
• the male rotor is usually the rotor that is directly driven

Question 4

Discharge ports

Answer 4

-the wider the discharge port the lower the pressure

Question 5

Built in pressure

Answer 5

-difference between the pressure at the inlet and the discharge

Question 6

Pressure ratio

Answer 6

-is a ratio of the absolute incoming air pressure to the absolute compressor discharge pressure

Question 7

Volumetric Efficiency

Answer 7

-back leakage where compressed air tries to get back through the compressor to the low suction pressure

Question 8

Capacity and discharge

Answer 8

-

Question 9

Asymmetrical vs. Symmetrical

Answer 9

-show pictures of each

Question 10

Compressor capacity

Answer 10

-rotor length, diameter, lobe/flutes design and speed

Question 11

Bearing locations

Answer 11

• fixed (tapered) bearing must be at the discharge end because the clearance has to be held there to hold pressure
• thrust bearings are required to maintain rotor position relative to the end plates

Question 12

Wet Screw

Answer 12

-

Question 13

Dry Screw

Answer 13

• needs timing gears

- able to provide oil free air

Question 14

Air Filters

Answer 14

-filters out air born shit to 3-5 microns

Question 15

Load/no load control (online/offline)

Answer 15

-throttle the inlet air either full opening the inlet valve or closing depending on pressure desired.

Question 16

Modulation control

Answer 16

• throttles the inlet air valve depending on what is required to adjust the work the compressor needs to do
• this would be beneficial when the compressor fluctuates between 60-90% capacity

Question 17

Displacement control

Answer 17

• also referred to as geometry control or internal bypass
• Turn, poppet and slide valves
• physically changes the opening and creates an opportunity for some of the air to return back to suction without being compressed.

Question 18

Minimum pressure valve

Answer 18

• to build minimum pressure inside the separator to get the oil flowing at start up
• located at the discharge of the air/water separator

Question 19

Vi (variable volume ratio control)

Answer 19

-uses a slide valve to adjust volume as needed

Question 20

Compressors capable of producing clean air?

Answer 20

• lobe blower

- dry screw