Displacement Compressors Compressor Types Air compressors Compressed Air Wiki Rotary screw compressors
When looking for the ideal rotary screw air compressor, it's important to understand how they work and the various types available. In this comprehensive guide, you'll find out more about how screw compressors work and why they might be the right choice for your needs.
A rotary screw air compressor is one of the two types of positive displacement gas compressors. It uses two rotors to create the 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.
Equivalent to positive displacement compressors are dynamic compressors, like centrifugal compressors. These machines use radial blades to force air out.
A screw compressor works with a male and female rotor that rotate in the opposite direction. This movement draws in air that is compressed as the space between the rotors and their housing decreases. The compressed air is then displaced to the outlet.
Each screw element has a fixed, built-in pressure ratio dependent on the length and pitch of the screw. As well as the form of the discharge port. To attain maximum efficiency, the built-in pressure ratio must be adapted to the required working pressure.
The speed of the rotors is optimized at a certain level to minimize mechanical losses (due to heat at very high speed) and volumetric losses (air losses due to very low speed).
There are two types of rotary screw air 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.
Read more about the differences between oil-free and oil-lubricated compressors.
There are also fixed-speed and variable-speed drive (VSD) variants. The basic difference is:
Modern, high-speed, oil-free screw compressors have asymmetric screw profiles. This arrangement results in significantly improved energy efficiency from reduced internal leakage.
External gears are most often used to synchronize the position of the counter-rotating rotors. As the rotors don’t come into contact with each other, nor with the compressor housing, no lubrication is required inside the compression chamber. Consequently, the compressed air is completely oil-free.
The built-in pressure ratio is limited by the limiting temperature difference between the inlet and the discharge. This is why oil-free screw compressors frequently work in several stages and interstage cooling to reach higher pressures.
One variant is known as an oil-flooded compressor or an oil-injected compressor. The technical name, however, is oil-lubricated.
Oil-lubricated rotary screw compressors inject oil into the compression chamber. This oil cools and lubricates the compressor element, helping remove heat while minimizing leakage in the compression chamber.
Oil-lubricated screw compressor elements can be manufactured for high-pressure ratios. One compression stage is usually sufficient for pressures up to 14 bar, and sometimes 17 bar, albeit at the expense of energy efficiency.
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.
Did you know? Utilizing VSD technology can achieve energy savings of 35-60%. Calculate your VSD energy savings.
One of the reasons for the great popularity of rotary compressors is their versatility. There really is the right rotary compressor for every application. Atlas Copco offers screw compressors with three types of drives, each with its own benefits.
If you’re running heavy-duty applications that continue over long periods of time, like in a factory, industrial plant or workshop, then you should consider upgrading to a rotary screw air compressor.
Benefits of a screw compressor in industry:
Not sure what type of rotary screw air compressor you need? Get in touch with Atlas Copco’s experts for personal advice and a tailored quote.
有許多原因能解釋為什麼迴轉式空壓機有如此高的需求：它們非常靈活、可靠、有效率、安靜，而且這種大受歡迎的全方位機器還有很多不同的版本。但是，哪一種最適合您呢？為了協助您找到符合需求的最佳解決方案，本指南概述不同的技術及其功能。
您想要討論貴公司的選項，或是您有特定的問題想要與我們討論？請按一下下方按鈕與我們聯絡。
30 June, 2022
There are a lot of things you have to consider when choosing an air compressor for your business. In this article we will explain what compressor is best suited for you, based on your application and needs.
22 February, 2022
Learn more about air compression and the different types of displacement compressors we know today. Here we’re talking about oil-lubricated and oil-free piston compressors.
16 March, 2023
There are two generic principles for the compression of air (or gas): Positive displacement compression and dynamic compression. This guide covers both.
