A rotary screw uses two rotors to push air through the compressor, which creates pressure. Compression is accomplished by the main and secondary rotors synchronously meshing in a one-piece, dual-bore housing. The main rotor has helical lobes and the secondary rotor has helical grooves. The air inlet port is located on top of the housing near the drive shaft end. The discharge port is near the bottom at the opposite end of the housing. 

In oil or water injected designs, fluid is introduced to remove the heat of compression, seal internal clearances, and prevent rotor-to-rotor contact. In oil-free designs, timing gears are attached to the rotor shafts to prevent rotor-to-rotor contact. Precision tolerances effect a seal. Water could still be injected into the compression chamber for cooling and sealing for higher pressures.

Limiting factors in rotary screw air compressors are the discharge temperature and pressure, and temperature and pressure differentials across the machine. These factors have an effect on rotor and housing expansion and deflections, housing strength, and bearing loads.

Multiple stages are used for improved efficiency and higher pressures. Some designs remove the oil and cool the air between stages in an intercooler, while others discharge the air and oil directly into the next stage.

Drives

There are three basic types of drives for air compressors: V-belt, direct, and gear. The choice depends on several factors, including the speed requirement of the compressor air end and the manufacturer’s preference. A fourth type is a combination of any of the above with a variable speed motor.

V-belt drives allow a smaller footprint for the enclosure. Alignment is not critical and maintenance is simplified.

Direct drives have alignment built-in. Belt and gear maintenance are eliminated. The footprint may be larger but the machine can run quieter.

Gear-driven airends eliminate alignment problems and are usually used for higher horsepowers. As with V-belts, compressor speed can be different from motor speed.

Variable speed drives (VSDs) usually alter the frequency of the incoming motor power. This approach is a simple way to vary compressor output and can be efficient if the airend has a wide efficiency range or flat efficiency curve over a wide speed range.

VSDs can boost the motor power factor to eliminate penalties from utility companies. The soft start feature reduces high input starting amps, another cost-saving aspect. Some drawbacks are additional initial cost and a power loss of 2-3% during full load operation. However, payback time is often realized within 3 yrs.

Screw compressors provide compressed air relying on high efficiency and very low noise levels thanks to the gearbox transmission. Today Screw Compressor can also be installed on an air vessel complete with refrigerant dryer and many options to improve efficiency and air quality.

High efficiency gear transmission

• Reduced energy consumption compared to belt driven technology.
• Low noise levels: Screw Compressor can be installed close to the workplace.
• Long service intervals.

Smart Controllers

• Easy to read thanks to the graphic screen (standard on IVR and optional on fixed speed machines).
• Energy saver with intelligent load/unload cycle control.
• Easily programmed with the working time you need 24/7.
• Complete with hardwire digital input and outstanding communication features.
• Fully compatible with Infologic and Airlogic family.

Highly efficient air filtration & oil separation

• High level air intake preventing larger dust particles from entering.
• Air intake on the cold part of the compressor ensures an optimum running temperature.
• 2 micron encapsulated filter guarantees only clean air enters the compressor, improving overall reliability.
• Oil separator ensures 3 ppm of oil carry over thanks to cyclonic, gravity and filter separation.

Types Of Screw Compressor.

• Gear Driven 1 – 2,2 kW / 1,5 – 3 hp 
• Belt Driven
• Direct Driven.
• Fixed drive and VSD option.
• Available range from 10HP – 50HP/7.5KW – 90KW Oil Injected.
• Compact integrated with inbuilt dryer
• Floor Mounted option
• Option of All in one tank mounted with air receiver, Refrigerant dryer, automatic drain and line filter.
• Option of Steel Screw head.
• Smart monitoring and control ES 4000 basic controller.
• Integrated inverter technology.
• Quite operation average 62dB(A).

Brands : Chicago Pneumatic, Worthington Creyssansac.