Intelligent Compressed Air: Rotary Air Compressors

Air Compressor
Air Compressor and Storage Tanks

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

Compressor Maintenance: Steps to Minimize Wear

While I was still in college, I worked in a meat processing plant as a Project Engineer in the maintenance department. During my time in the maintenance department I learned the importance of proper maintenance on machines. A meat processing plant is one of the most taxing environments on machines as they will have to survive in extreme cold temperatures to extreme hot temperatures; they are also put through deep sanitation wash downs multiple times a day sometimes for periods of over an hour. The plant really put into perspective the importance of preventative maintenance of machines. This includes utilities such as a boiler and of course your air compressor.

Industrial Air Compressors
Neglected air compressors can cause a lot of issues ranging from expensive repairs to a decrease in efficiency. Wear and tear placed on the motor of an air compressor can cause the compressor to produce less compressed air (SCFM) at the same power consumption. This means you are paying the same amount of money for less compressed air.

A primary focus to prevent an increased amount of wear on your compressor motor is to seal up compressed air leaks. Leaks can cause the compressor to cycle more often and/or refill receiver tanks on a more frequent basis, causing the motor to run more often. With the motor having to run more often to keep the air present, it will wear down faster. Using EXAIR’s Ultra Sonic Leak detector, leaks can be found in the pipes so that they can be sealed up.

EXAIR Ultrasonic Leak Detector
Another important maintenance is to make sure that the compressor gets cleaned. As the motor runs excess heat is generated; the heat generated then needs to be dissipated which is done by exhausting air through vents. If these vents become dirty or blocked and the air cannot escape then the temperature of the motor and winding resistance will increase; this in turn will shorten the life of the motor and increase the energy consumption. Using one of EXAIR’s Super Air Nozzles is a sure way to keep your compressor vents clean and dust free in a quiet and efficient manner.
EXAIR Nozzles
There are many other items that require maintenance over time such as keeping belts in good condition and the drain traps clean. Good maintenance on any item whether it’s a production machine or  air compressor keeps it running a peak performance helping you save money and headaches in the long run. 

If you have any questions about compressed air systems or want more information on any EXAIR’s of our 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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Centrifugal Air Compressors: What are they?

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, controls 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. For the purposes of this blog, I’m going to highlight the most common style of dynamic compressor: the centrifugal air compressor.

Dynamic compressors are composed of two main categories: axial and centrifugal. These types of compressors raise the pressure of air or gas by imparting velocity energy and converting it to pressure energy. In a centrifugal air compressor, air continuously flows and is accelerated by an impeller. This impeller can rotate at speeds that exceed 50,000 rpm. Centrifugal air compressors are generally much larger and can accommodate flow ranges of 500-100,000 CFM, although they’re more commonly used in the range of 1,000 CFM to 5,000 CFM.

Centrifugal Pic 1

In a centrifugal compressor, kinetic energy is transformed into pressure energy inside of the diffuser. The air passes through the inlet guide vanes and is drawn into the center of a rotating impeller. The impeller has radial blades that push outward from the center due to centrifugal force. This radial movement of air causes an increase in pressure and the generation of kinetic energy. This kinetic energy is then also converted into pressure as it passes through the diffuser.

According to the Compressed Air Challenge, some advantages of the centrifugal air compressor include:

  • Completely packaged for plant or instrument air up through 1,000 HP
  • Relative first cost improves as the size increases
  • Designed to deliver lubricant-free air
  • Do not require special foundations
  • Ability to deliver large volumes of air (up to 100,000 CFM)

Some disadvantages include:

  • Limited capacity control
  • Poor part-load efficiency
  • High rotational speeds require special bearings, sophisticated monitoring of vibrations and clearances resulting in specialized maintenance considerations
  • High initial purchase cost

A centrifugal air compressor is just one of the many different styles utilized in industry to supply a variety of point of use compressed air products. If you have an application in your facility that could benefit from an engineered solution, give us a call. An Application Engineer would be happy to discuss your options with you and see to it that you’re getting the most out of your compressed air!

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

 

Image courtesy of the Compressed Air Challenge

 

Air Compressor Motors And Controls

Electric motors are by far the most popular drivers for industrial air compressors.  Indeed, they are the prime movers for a great many types of industrial rotating equipment.  In their simplest form of operation, rotary motion is induced when current flows through a conductor (the windings) in the presence of a magnetic field (usually by electricity inducing a magnetic field in the rotor.)  In the early days, you’d start one up by flipping a big lever called a knife switch.

Example of a knife switch

These are cumbersome and inherently dangerous…the operators literally have their hand(s) on the conductor.  If the insulation fails, if something mechanical breaks, if they fail to make full contact, electrocution is a very real risk.  Over time, motor starters came in to common use.  Early in their development, they were more popular with higher HP motors, but soon were made for smaller motors as well.

There are several types of modern motor starters:

Full Voltage Starters: The original, and simplest method.  These are similar in theory to the old knife switches, but the operator’s hands aren’t right on the connecting switch.  Full line voltage comes in, and amperage can peak at up to 8 times full load (normal operating) amperage during startup.  This can result in voltage dips…not only in the facility itself, but in the neighborhood.  Remember how the lights always dim in those movies when they throw the switch on the electric chair?  It’s kind of like that.

Reduced Voltage Starters: These are electro-mechanical starters.  Full line voltage is reduced, commonly to 50% initially, and steps up, usually in three increments, back to full.  This keeps the current from jumping so drastically during startup, and reduces the stress on mechanical components…like the motor shaft, bearings, and coupling to the compressor.

Solid State (or “Soft”) Starters: Like the Reduced Voltage types, these reduce the full line voltage coming in as well, but instead of increasing incrementally, they gradually and evenly increase the power to bring the motor to full speed over a set period of time.  They also are beneficial because of the reduced stress on mechanical components.

The Application Engineering team at EXAIR Corporation prides ourselves on our expertise of not only point-of-use compressed air application & products, but a good deal of overall system knowledge as well.  If you have questions about your compressed air system, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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