Sliding Vane Air Compressors

Over the last few months, my EXAIR colleagues have blogged about several different types of air compressor types including single and double acting reciprocating and rotary screw. (You can select the links above to check those out.) Today I will review the basics of the sliding vane type, specifically the oil/lubricant injected sliding vane compressor.

The lubricant injected sliding vane compressor falls under the positive displacement-type, the same as the other types previously discussed.  A positive displacement type operates under the premise that a given quantity of air is taken in, trapped in a compression chamber and the physical space of the chamber is mechanically reduced.  When a given amount of air occupies a smaller volume, the pressure of the air increases.

Each of the previous positive displacement type compressors use a different mechanism for the reduction in size of the compression chamber.  The single and double acting reciprocating use a piston that cycles up and down to reduce the compression chamber size. The rotary screw uses two inter-meshing rotors, where the compression chamber volume reduces as the air approaches the discharge end.  For the lubricant sliding vane type, the basic design is shown below.

Sliding Vane2
Air enters from the right, and as the compression chamber volume reduces due to counterclockwise rotation, the pressure increases until the air discharges to the left

The compressor consist of an external housing or stator, and the internal circular rotor, which is eccentrically offset.  The rotor has radially positioned (and occasionally offset) slots in which vanes reside.  As the rotor rotates, the centrifugal forces on the vanes cause them to move outwards and contact the inner surface of the stator bore.  This creates the compression areas, formed by the vanes, rotor surface and the stator bore.  Because the rotor is eccentrically offset, the volume of the compression area reduces as the distance between the rotor surface and the stator reduces.  As the rotor turns counterclockwise, the vanes are pushed back into the rotor slots, all the while in contact with the stator surface.  The shrinking of the compression area leads to the increase in air pressure.

Oil is injected into compression chamber to act as a lubricant, to assist is sealing, and to help to remove some of the heat of compression.

The advantages of the lubricant sliding vane compressor type is very similar to the lubricant injected rotary screw.  A few key advantages include:

  • Compact size
  • Relatively low initial cost
  • Vibration free operation- no special foundation needed
  • Routine maintenance includes basic lubricant and filter changes

A few of the disadvantages include:

  • Lubricant gets into the compressed air stream, requires an air/lubricant separation system
  • Requires periodic lubricant change and disposal
  • Less efficient than rotary screw type
  • Not as flexible as rotary screw in terms of capacity control in meeting changing demands

EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.

If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer

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Photo Credit to Compressed Air Challenge Handbook

Rotary Air Compressors: How Do They Work?

Ingersoll Rand Rotary Screw Compressor

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, control systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy. We’ve discussed the different styles of air compressors here on the EXAIR Blog in the past. Today I’d like to highlight the rotary compressors, one of the positive-displacement types of compressors.

Positive-displacement compressors are broken into two categories: reciprocating and rotary. The rotary compressors are available in lubricant-injected or lubricant-free varieties. Both styles utilize two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point inter-meshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure.

In the lubricant-injected varieties, the compression chamber is lubricated between the inter-meshing rotors and bearings. This lubricant protects the inter-meshing rotors and associated bearings. It eliminates most of the heat caused by compression and acts as a seal between the meshing rotors and between the rotor and stator. Some advantages of the lubricant-injected rotary compressor include a compact size, relatively low initial cost, vibration free operation, and simple routine maintenance (replacing lubricant and filter changes). Some drawbacks to this style of compressor include lower efficiency when compared with water-cooled reciprocating compressors, lubricant carry over must be removed from the air supply with a coalescing filter, and varying efficiency depending on the control mode used.

In the lubricant-free varieties, the inter-meshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an inter-cooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

Each of these compressors can deliver air to your Intelligent Compressed Air Products. If you’re looking to reduce your compressed air consumption and increase the safety of your processes contact an EXAIR Application Engineer today. We’ll be happy to discuss the options with you and make sure you’re getting the most out of your compressed air usage.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD




Photo courtesy of Ingersoll Rand CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=32093890

Sliding Vane Compressors: How they Work

When it comes to air compressors there are many different types to choose from. Each compressor performs differently and have their own benefits and downfalls. In this case we will be taking a look a Sliding Vane Compressor which is a positive-displacement compressor. Positive-displacement type compressors have a given amount of air or gas that gets trapped in a compression chamber. From there the volume of that air is mechanically reduced causing an increase in the pressure. Sliding vane compressors use a circular stator that is housed in a cylindrical rotor; the rotor contains radially positioned slots where the vanes reside. These vanes are what create the compression in the “cells”.

Diagram of a sliding vane compressor

The inlet port on the system is positioned in a way that allows the air flow into each cell, optimizing the amount of air that each cell can hold. Once the air enters the system the cell size is reduced down farther and farther as rotation continues and each vane is pushed back into its original slot in the rotor. Compression will continue until each cell reaches the discharge port. One of the more common forms of a sliding vane compressor is the lubricant injected variety. These compressors inject a lubricant into the chamber to lubricate the walls and the vanes; this removes the heat of compression, as well as provide a seal on the cell. These air compressors are generally sold in a 10 – 200 HP range with capacities running between 40 – 800 acfm.

Advantages of a lubricant injected sliding-vane compressor include:

  • Compact size
  • Relatively low purchase cost
  • Vibration-free operation does not require special foundations
  • Routine maintenance includes lubricant and filter changes

Some of the disadvantages that come with this type of compressor:

  • Less efficient than the rotary screw type
  • Lubricant carryover into the delivered air will require proper maintenance of an oil-removal filtration system
  • Will require periodic lubricant changes

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Photo Credit to Compressed Air Challenge Handbook

About Sliding Vane Air Compressors

In positive-displacement type compressors, a given quantity of air or gas is trapped in a compression chamber. The volume of this air is then mechanically reduced, causing an increase in pressure. A sliding-vane compressor will consist of a circular stator that is housed in a cylindrical rotor. The rotor then has radially positioned slots where the vanes reside. While the rotor turns on its axis, the vanes will slide out and contact the bore of the stator wall. This creates compression in these “cells”.

An inlet port is positioned to allow the air flow into each cell, allowing the cells to reach their maximum volume before reaching the discharge port. After passing by the inlet port, the size of the cell is reduced as rotation continues and each vane is then pushed back into its original slot in the rotor.  Compression will continue until the cell reaches the discharge port. The most common form of sliding-vane compressor is the lubricant injected variety. In these compressors, a lubricant is injected into the compression chamber to act as a lubricant between the vanes and the stator wall, remove the heat of compression, as well as to provide a seal. Lubricant injected sliding-vane compressors are generally sold in the range of 10-200 HP, with capacities ranging from 40-800 acfm.

 

Sliding Vane
Air enters from the right, and as the compression chamber volume reduces due to counterclockwise rotation, the pressure increases until the air discharges to the left

Advantages of a lubricant injected sliding-vane compressor include:

  • Compact size
  • Relatively low purchase cost
  • Vibration-free operation does not require special foundations
  • Routine maintenance includes lubricant and filter changes

Some of the disadvantages that come with this type of compressor:

  • Less efficient than the rotary screw type
  • Lubricant carryover into the delivered air will require proper maintenance of an oil-removal filtration system
  • Will require periodic lubricant changes

With the host of different options in compressor types available on the market, EXAIR recommends talking to a reputable air compressor dealer in your area to help determine the most suitable setup based on your requirements. Once your system is up and running, be sure to contact an EXAIR Application Engineer to make sure you’re using that compressed air efficiently and intelligently!

Jordan Shouse
Application Engineer
Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_JS

 

Photo Credit to Compressed Air Challenge Handbook