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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Compressed Air System Maintenance

Air Compressor and Storage Tanks

Compressed air is the life blood of a manufacturing plant, and the air compressor would be considered the heart. To keep things “fit”, it is important to check all areas and to optimize your system to keep your plant running safely and efficiently. You do not have to be a doctor to do these “operations”. If your compressor fails, the entire facility will stop working. In this blog, I will cover some simple preventative maintenance that can really help you.

As margins get tighter and cost of manufacturing climbs, industries are looking into other areas to be more economical. A big focus today is the compressed air system. Compressed air is considered to be a “forth” utility behind gas, water, and electricity, and it is a necessary to run your pneumatic systems. But it is the least efficient of the utilities. So, it is very important to use this utility as practical as possible and to use a PM program to keep it going.

If we start at the beginning of your compressed air system, this would jump us to the air compressor. This is the machine that uses an electric or gas motor to spin a crank. It compresses the ambient air into a small volume to generate stored energy to be used by your pneumatic systems. Because the air compressor is complex and intricate, I would recommend a trained service personnel to do the maintenance. But, if your staff is familiar with air compressors, I wrote a blog to help look at certain parts periodically. You can read it here: “6 Basic Steps for Good Air Compressor Maintenance (And When to Do Them)”.

The next part after the air compressor is to look at the aftercoolers, compressed air dryers, receiver tanks, filters, and condensate drains. Some facilities may only have some of these items.

The aftercoolers are designed to cool the exit air from your air compressor. It uses a fan to blow ambient air across coils to lower the compressed air temperature. It is easy to check the fan to verify that it is spinning and to keep the coils clean from debris.

The compressed air dryers can range in size and type. For the refrigerant type air dryers, you should periodically check the freon compressor with ohm and amp readings, the condensers for cleaning, and the super heat temperature as well. For desiccant type air dryers, you will need to check the operation of the valves. Valves are used to regenerate one side of the desiccant bed. The valves can fail and stick either open or closed. In either way, if the desiccant cannot regenerate, then it will allow moisture to go down stream and eventually destroy the desiccant beads.

The receiver tanks have safety relief valves that will need to be checked to make sure that they are not leaking. If they are, they should be changed.

As for the filters, they collect contamination from the compressed air stream. This will include liquid water, oil, and dirt. A pressure drop will start to increase with the contaminants, which will reduce the potential energy. If they do not have pressure drop indicators, you should have two points of references for pressure readings. You should change the filter elements when the pressure drop reaches 10 PSID (0.7 bar) or after 1 year.

With all these items above, water is created. There should be condensate drains to discard the water. The most efficient types of condensate drains are the zero loss drains. Most condensate drains will have a test button to be pressed to verify that they open. If they do not open, they should be replaced or fixed. Do not place a valve on them and partially open for draining. For float type drains, they will have a pin inside that can be pressed to open. You can verify that all the liquid has been expelled.

The distribution system are the pipes and tubes that run compressed air from the supply side to the demand side of your pneumatic system. One of the largest problems affecting the distribution system are leaks. That quiet little hissing sound from the pipe lines is costing your company much money. A study was conducted by a university to determine the percentage of air leaks in a typical manufacturing plant. In a poorly maintained system, they found on average of 30% of the compressor capacity is lost through air leaks.

To put a dollar value on it, a leak that you cannot physically hear can cost you as much as $130/year. That is just for one inaudible leak in hundreds of feet of compressed air lines. Unlike a hydraulic system, compressed air is clean; so, leaks will not appear at the source. So, you have to find them by some other means.

Digital Flowmeter

 

EXAIR Ultrasonic Leak Detector

Most leaks occur where you have threaded fittings, connections, hoses, and pneumatic components like valves, regulators, and drains. EXAIR has two products in our Optimization product line that are designed to help find leaks in your compressed air system.

The Ultrasonic Leak Detectors can find air leaks, and the Digital Flowmeters can monitor your system for loss of air. When an air leaks occur, it emits an ultrasonic noise caused by turbulence. These ultrasonic noises can be at a frequency above audible hearing for human. The EXAIR Ultrasonic Leak Detector can pick up these high frequencies to make inaudible leaks audible.

With the Digital Flowmeters, you can continuously check your system for waste and record it with a USB Datalogger.  Air leaks can occur at any time within any section of your pneumatic system.  With a Digital Flowmeter, you can also isolate an area to watch for any flow readings; telling you that the air is leaking in that section.  With both products included in your leak-preventative program, you will be able to reduce your waste and optimize your compressed air system.

Family of Nozzles

At the point-of-use areas, this is the easiest target area for compressed air maintenance. If you are using open tubes or drilled pipes for blowing, they are loud, inefficient, and unsafe. They can be easily change to an engineered blow-off product from EXAIR which are very efficient and OSHA safe. EXAIR offers a range of Super Air Nozzles and Super Air Knives to simply replace the current blow-off devices that overuse compressed air. If we go back to the beginning of your system, the air compressor is a mechanical device which will have a MTBF, or Mean Time Between Failures. The hour meter on your air compressor is like a life monitor. By using less compressed air, your air compressor will extend that time in MTBF.

Keeping your compressed air system running optimally is very important for a business to run. With a simple maintenance program, it can help you with your pneumatic operations and energy savings. Like stated above, your compressed air system is the life blood of your company, and you do not need a PhD to keep it well maintained. Just follow the target areas above. If you would like to discuss further about the health of your compressed air system, you can contact an Application Engineer at EXAIR. We will be happy to help “diagnose” a solution.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

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