Screw Compresors Flashcards
What are the two basic types of screw compressors?
- Single Rotor
* Dual Rotor
Which design is more common, Dual or Single rotor?
- Dual Rotor is by far the more common
What are the two category of dual rotor of screw compressors?
- Wet Screw/Oil-flooded
* Dry Screw/Oil-Free
What do some oil-free screw compressors incorporate for cooling and sealing?
A water spray
What do dry screw compressors require to prevent rotor contact?
- Timing Gears
Describe built-in pressure ratio?
The compressor is designed to reach its built-in pressure ratio just before it discharges into the discharge port. (This pressure cannot be altered) Once the pockets of air are exposed to the discharge port the pressure becomes the same as the compressed air line or receiver.
What are the two lobe profiles?
- Symmetrical
* Asymmetrical
Which profile is the most commonly used?
The Asymmetrical profile.
Why is the asymmetrical profile more common?
The asymmetrical profile is the most commonly due to it’s improved efficiency and increased delivery volume.
What capacities do screw compressors delivers?
They deliver air at lower pressure Usually at 100 to 175 PSI, whit volumes ranging from 25 to 8500 CFM
What determines the pressure ratio of the system?
*The location and size of the inlet port.
Note: A wider discharge port will allow air/gas to exit sooner, resulting in pressure drop.
Where must the fixed bearing be install to keep critical clearance distances to prevent leakage past the flutes?
The fixed bearings must be located on the discharge end.
Compressors manufactured in North America uses what type of bearings on the discharge end?
*Tapered Roller Bearings.
Compressors manufactured in Europe uses what type of bearings on the discharge end?
*Angular Contact Bearings.
Describe a single rotor screw (Mono-Screw)
The single rotor screw has only one main rotor with two meshing star shaped rotors.
What is the purpose of the two star rotors on opposite sides of the main rotors?
They reduce the side loading on the bearings while producing two compressions simultaneously.
What are the operating pressures for an Oil-Flooded (Wet) Screw Compressor?
100-125 PSIG and is common for them to run 40 000 to 100 000 hours?