A rotary screw air compressor is one of the two types of positive displacement gas compressors. It uses two rotors to create pressure needed for air compression. They are one of the easiest types of air compressors to use and maintain.
The other type of positive displacement compressor is the reciprocating or piston compressor.
The main screw compressor parts are the male and female rotors, which rotate in opposite directions. This movement draws in air that is compressed as the space between the rotors and their housing decreases.
Each screw element has a fixed, built-in pressure ratio dependent on the length and pitch of the screw, and form of the discharge port. To attain maximum efficiency, the built-in pressure ratio must be adapted to the required working pressure
Oil-free or dry screw compressors
Oil-lubricated screw compressors
In oil-lubricated screw compressor technology, the male rotor drives the female rotor.
In oil-free compressor technology, a timing gear drives both rotors for harmonic running, with minimum calculated clearance between both elements.
The basic difference between fixed speed and variable speed drive (VSD) compressors is found in their name:
Fixed speed compressors run at a continuous fixed speed
Variable speed drive (VSD) technology turns the motor at the appropriate speed in relation to the amount of air that is required.
Fixed speed compressors are very efficient when continuously operating at 100% capacity, but most facilities don’t require that amount of productivity. Before the motor comes to a complete stop, it will continue to run while no air is being produced, consequently wasting energy and money.
Such inefficiency and waste is generally found at facilities operating multiple shifts and experiencing flow demand fluctuation throughout the day.
VSD compressors increase the speed of the motor as the need for air increases, thus supplying more flow/CFM. If the demand decreases, the motor will automatically slow down and only use the required energy to provide appropriate flow.
On slow production days, breaks in workflow, or throughout second and third skeleton shifts, VSD technology is especially handy. This type of air compressor saves electricity and money, compared to fixed speed models.
Since compressed air energy usage accounts for over 80% of an air compressor's costs, it's important to choose efficient equipment. Utilizing VSD technology can achieve energy savings of 35-60%.
Energy efficiency
Low noise output
Small footprint
Continuous operation at temperatures of up to 46 degrees C
Low oil carry-over (as little as 3 ppm) in oil-lubricated machines
Zero loss of capacity over time
Life expectancy between 60,000 – 80,000 hours
Reliability
