No matter which industry you are in, rotary compressor applications can be wide and varied. Based on your application, you will certainly find a compressor that fits your needs. Such is the versatility of this compressor type! Being energy-efficient, highly reliable, and low on maintenance, rotary compressors are the top choice across industrial sectors.
Selecting the right compressor for your unit is a tough job because different types of rotary compressors are offered on the market today. So, taking a pick from a pool of choices can unnerve even the most experienced buyers. In this article, we discuss the four main types of rotary compressors to help you make the right choice for your application.
What is rotary compressor and how does it function?
To release pressurised air, rotary compressors are designed as per Boyle’s Law, which states that the pressure exerted by a gas shares an inversely proportional relationship with the volume the gas occupies. However, this occurs under the condition when the gas amount and temperature remain the same within a closed chamber.
In rotary compressors, the air enters from the inlet port and moves through a chamber, which has rotating parts like rotary screws or vanes. Air enters from the inlet port, and is compressed inside the chamber where lubircation fliud is injected into the air (for oil-injected compressors) - its volume decreases and thereby pressure increases. Also, the rotating elements move in a particular way which causes an increase or decrease in the volume of the chamber. The mixture of air and oil flows to the separator where oil is removed from the mixture and air flows through to the coolers for condensate removal before being led to outlet of the system.
Rotary compressors unlike piston compressors, don’t really have inlet or outlet valves, instead, they have discharge and suction ports which are alternatively covered and exposed by the rotating parts.
On another point, we also often get asked how rotary compressors are better than piston ones. Here’s a blog highlighting piston vs rotary compressor so that you can gain deeper insights.
What are the main types of rotary compressors?
Even rotary compressors run on different mechanisms. In this section, we tell you what different rotary compressor types are and how to pick the right compressor for your applications.
- Lobe Type – As for the lobe type compressors, the air enters the chambers, which have two spinning wheels with small pockets at opposite ends. The air fills in the pocket and gets pushed to the chamber’s opposite side, being compressed in the shrinking space. However, lobe compressors may not be an ideal fit for applications requiring heavy duty continous airflow and high pressures.
- Vane Type – In this type of rotary compressor, the vanes are offset inside the chamber. When air enters the inlet, rotating vanes move the air to the tighter edge, compressing it using little effort only. Although they are easy to use, the vanes of this compressor can wear out and get less effective over time. Replacement can be a good solution to restore its efficiency.
- Scroll Type – The internal parts of the scroll type compressors comprise two scrolls and spirals, out of which, one remains stationary. When air enters along the scroll’s edge, it is pulled inside the spiral in tight circles before being forced down the centre outlet. Smaller than screw compressors, these compressors are ideal for carrying out intermittent applications in limited spaces.
- Screw Type – If you wanted to know the most popular rotary compressor, here we are. In fact, screw-type compressors dominate the compressor market for being highly reliable. Inside these compressors, you’ll find two large screws rotors rotating against one another – the male and female rotors. As the air enters through an inlet port, it is pulled in between the screws. While moving through the screw, the air gets compressed due to less space. Ultimately, the compressed air is then released through the outlet. Moreover, the screw element rotor desgin of 4/6 lobe combination is proven to be the most efficient in its class.
Rotary screw type
Types of screw rotary compressors
Along with the variety comes speciality, where you might want to choose the right rotary compressor for your purpose. In this section, we take you through different types of leading screw rotary compressor technologies available on the market today.
- Oil-free Screw – As the technology evolved, modern, high-speed, oil-free screw compressors were introduced with asymmetric screw profiles. This resulted in significantly improved energy efficiency, due to reduced internal leakage.
Superior teflon coated oil-free screw to minimize clearance between rotors
- Oil-injected Screw – For oil-injected screw compressors, a liquid is injected into the compression chamber and frequently into the compressor bearings. It functions as a coolant and lubricates the compressor element’s moving parts, to cool the air being compressed internally. This also further reduces the return leakage to the inlet.
Today, oil is the most commonly injected liquid due to its high lubricating and sealing properties. Oil-injected screw compressor elements can be manufactured for high-pressure ratios, which would include one compression stage that is usually sufficient for pressure up to 14 and two stage to achieve 20 bar with direct drive for minimum losses and improved overall design for maximum operation efficiency and faster maintenance – like sliding type coolers, filter cateridge replacment for separators or IP66 IE5 Permanent Magnet service free motors.
Oil-injected rotary screw element
What makes screw compressors superior to other types?
There are many speculations on why the Screw Compressors are considered to be superior to other types of compressors, let’s make this easier for you with the following information.
The primary advantages of screw compressors are:
- Suitable for continous heavy duty load for large volumes of air
- Specific power consumption and discharge capacities remain the same overtime as no suction/ discharge valves used or no cylinder deformation occurs
- Maintenance - consumption of general spare parts is much lower and faster servicing times
- Relatively low temperatures of compressed air
- Lower noise levels
- Negligible vibration levels
At Atlas Copco, our rotary screw compressors give you energy savings of about 30 to 50% and with an integrated Variable Speed Drive option can be further beyond! And we’ve made them simple to dismount and maintain so that you save on labor costs as well. Expect to have a plug-and-play style of experience! We also provide a complete solution that includes training, performance analysis and support from our engineering department. To enquire about cutting-edge rotary compressors, please connect with our distributor in Bahrain.
