Tag: air dryer

Dew Point and Water in Compressed Air: Understanding the Effects

Published on by John BallLeave a comment

In systems, it is important to understand the type of medium that is being used.  For most EXAIR products, this will be compressed air.  As the air compressor draws in ambient air, it also brings in dust, contamination, and moisture into the system.  If untreated, the pneumatic system will have to contend with these foreign “invaders” that will affect the performance of your pneumatic devices.  One of the most common problems is water.

Water enters the compressed air system from the water vapor already present in the ambient air, which is referred to as the dew point or relative humidity.  When you take ambient air and compress it, the amount of “elbow room” for the water vapor decreases.  This causes the water vapor to condense and create liquid water.  It would be similar to a water-soaked sponge.   As you compress it with your hands, the sponge will not be able to hold on to the water.  Similarly, as the air is compressed, water will start to form and fall out into the compressed air system.  Water is a by-product of a compressed air system.

Visual depiction of the impact of water vapor contained amongst air particles and how this reduces available volume during compression.

The definition for determining if liquid water is present in your system is called the pressure dew point.  Dew point is the temperature at which water vapor will condense and form water droplets.  If the dew point temperature and the air temperature are equal, then the air is considered 100% saturated (water vapor will start to condense to form water droplets).  In compressed air systems, air dryers are used to reduce the dew point temperature.  This means that unless the ambient temperature falls below the dew point temperature, water vapor will not condense into a liquid state.

There are two major types of compressed air dryers; refrigerated and desiccant.  The refrigerated air dryers are the most common, and the dew point is measured at about 39oF (4oC).  So, unless the air temperature gets close to freezing, i.e., the piping system that goes outside in cold weather, water should not be present.  Desiccant air dryers can achieve dew points as low as -40oF (-40oC).  This compressed air is very dry and can be used for medical systems, food and beverage processing, and instrument air.  The reason is that bacteria cannot survive in compressed air that is that dry.  The other types are dewpoint reducing systems, which include membrane and deliquescent dryers. 

Good engineering practice calls for point of use filtration and moisture removal, such as that provided by EXAIR Filter Separators.

For most pneumatic devices, a Filter Separator with an auto-drain should be used as a minimum amount of protection.  Even with systems that have compressed air dryers as described above, they are mechanical devices.  So, failures can occur.  You should review your compressed air system to ensure that your pneumatic system, including EXAIR products, is operating at peak efficiency.  This will include your supply system, compressed air leaks, and blow-off devices. 

Moisture-laden compressed air can cause issues such as increased wear on the pneumatic tools, the formation of rust in piping and equipment, quality defects in painting processes, and frozen pipes in colder climates.  Regardless of what products you’re using at the point-of-use, a compressed air dryer is undoubtedly a critical component of the compressed air system.  Providing clean, dry air to EXAIR Products or other pneumatic devices will help to extend the life of your equipment.  If you wish to discuss more about your compressed air system or how EXAIR can provide a more efficient way to use that compressed air, an Application Engineer will be happy to assist you.

John Ball
International Application Engineer


Email: johnball@exair.com
Twitter: @EXAIR_jb

Refrigerated Air Dryers

Published on by John BallLeave a comment

Whenever air gets compressed, it reduces the space for the water molecules to remain as a vapor; which causes condensation.  For this, compressed air dryers are an important part of a compressed air system.  They are designed to remove moisture to prevent condensation further downstream in the system.  The three main types of dryers are refrigerated, desiccant, and membrane. For this blog, I will cover the refrigerant-type compressed air dryers.

Compressed air dryers are rated with a dew point rating.  A dew point is the temperature at which the air has a relative humidity of 100%.  Since the air cannot become more saturated with water than 100%RH, water will condense and fall out like “rain”.  You can see this effect during the cool mornings when dew forms on the grass.  Compressed air dryers are designed to reduce the dew point temperature of your compressed air.  For a refrigerant type, they are near the dew point temperature of 38oF (3oC).  Like a refrigerator, they use refrigerant to cool the compressed air.  We cannot go below this temperature as it could form ice inside the dryer.  But, as long as the ambient temperature does not go below 38oF (3oC), liquid water will not be present in the pneumatic system. 

There are two main types of refrigerated air dryers; cycling and non-cycling.  Cycling type refrigerant air dryers will cool a liquid mass, generally a glycol-water mixture, to a set-point and turn off.  The liquid will go through an air-to-liquid heat exchanger to remove the heat from the compressed air.  Referring to the cycling action, when the liquid mass goes above the set point, the refrigeration system will restart and cool the liquid mass again.  The cycling refrigerant air dryers are more expensive, but they are more efficient. 

Non-cycling refrigerant air dryers are more common.  The refrigeration system continues to run through an air-to-air heat exchanger to cool the compressed air.  It is similar to your AC system in your car.  With this type of system, they are more susceptible to the environment, i.e., temperature, elevation, and humidity.  So, adjustments are required for proper installation. 

With both types of refrigerant dryers, the internal compressed air section is very similar.  They will have a filter separator to remove the liquid that is created from the condensation from the cold temperatures.  They also have an additional air-to-air heat exchanger.  This will provide two important features for the refrigerated air dryers.  As the cold air leaves the refrigerant section, it helps to cool the incoming compressed air.  This will make the system more efficient.  And as the hot incoming compressed air helps to warm the cold air leaving the dryer, it will stop the condensation of liquid water on the outside of the pipes.  Like the dew forming on the grass during cool mornings, the same will occur with the compressed air piping system. 

Moisture-laden compressed air can cause issues such as increased wear on the pneumatic tools, the formation of rust in piping and equipment, quality defects in painting processes, and frozen pipes in colder climates.  Regardless of what products you’re using at the point-of-use, a compressed air dryer is undoubtedly a critical component of the compressed air system.  Delivering clean, dry air to your EXAIR Products or other pneumatic devices will help to ensure a long life out of your equipment.  If you wish to discuss more about your compressed air system or how EXAIR can provide a more efficient way to use that compressed air, an Application Engineer will be happy to assist you. 

John Ball, CCASS


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

Photo: Grass morning dew by RuslanSikunov.  Pixabay License

Compressed Air System Equipment – What You Need To Know

Published on by Russ BowmanLeave a comment

The use of compressed air in industry is so widespread that it’s long been called “the fourth utility” (along with electricity, water, and natural gas). As a function of energy consumption (running an air compressor) to energy generated (operation of pneumatic equipment), only 10-15% of the energy consumed is converted to usable energy stored as compressed air. Its “bang for the buck”, however, comes when you consider the total cost of ownership – yes, it costs a lot to generate, but:

  • It’s relatively safe, when compared to the risks of electrocution, combustion, and explosion associated with electricity & natural gas.
  • Air operated tools, equipment, and products are generally much cheaper than their electric, gas, or hydraulic powered counterparts.
  • Air operated products, like anything, require periodic maintenance, but oftentimes, that maintenance simply comes down to keeping the air supply clean and moisture free, unlike the extensive (and expensive) maintenance requirements of other industrial machinery.

Even with these advantages, though, it’s still critical to get all you can out of that 10-15% of the energy you’re consuming to make that compressed air, and that starts with having the right stuff in the right place. Now, all of the following “stuff” might not apply to every compressed air system. I once worked in a repair shop, for example, with a small compressor that was used for a couple of blow off guns, impact drivers, and a sidearm grinder. I’ve also done field service in facilities with hundreds of pneumatic cylinders & air motors that operated their machinery. Those places had even more “stuff” than I’m devoting space to in this blog, but here’s a list of the “usual suspects” that you’ll encounter in a properly designed compressed air system:

  • Air compressor. I mean, of course you need a compressor, but the size and type will be determined by how you’re going to use your air. The small repair shop I worked in had a 5HP reciprocating positive displacement compressor with a 50 gallon tank, and that was fine. The larger facilities I visited often had several 100 + HP dynamic centrifugal or axial compressors, which get more efficient with size.
  • Air preparation. This includes a number of components that can be used to cool, clean, and dry the air your compressor is generating:
    • Pressurizing a gas raises its temperature as well. Hot compressed air could cause unsafe surface temperatures and can damage gaskets, seals, and other components in the system. Smaller compressors might not have this problem, as the heat of compression is often dissipated through the wall of the receiver tank and the piping at a rate sufficient to keep the relatively low (and often intermittent) flow at a reasonable temperature. Larger compressors usually come with an aftercooler.
    • The air you compress likely has a certain amount of moisture in it…after nitrogen and oxygen, water vapor usually makes up more of the content of atmospheric air than all other trace gases combined. There are a number of air dryer types; selection will be dictated by the specifics of your facility.
    • Your air is going to have other contaminants in it too. We did welding & grinding in the repair shop where our compressor sat in the corner. We kept a few spare intake filters handy, and replaced them regularly. In conjunction with the aftercooler & dryer, larger industrial compressors will also have particulate filters for these solids. For extra protection, coalescing filters for oil vapor, and adsorption filters for other gases & liquid vapors, are specified.
  • Distribution. In the repair shop, we had a 3/4″ black iron pipe that ran across the ceiling, with a few tees & piping that brought the air down to the individual stations where we used it. The larger facilities I visited had larger variations of this “trunk and branch” type network, and some were even big enough to make use of a loop layout…these were especially popular when multiple air compressors were located throughout the facility. In addition to black iron, copper & aluminum pipe (but NEVER PVC) are commonly used too.
  • Condensate removal. The small repair shop compressor had a valve on the bottom of the tank with a small hose that we’d blow down into a plastic jug periodically. Larger systems will have more complex, and oftentimes automated condensate management systems.

So, that’s the system-wide “stuff” you’ll usually encounter in a properly designed compressed air system. After that, we’ll find a number of point-of-use components:

  • Air preparation, part 2. The compressor intake & discharge filtration mentioned above make sure that you’re putting clean air in the distribution piping. That’s fine if your distribution piping is corrosion resistant, like aluminum or copper, but black iron WILL corrode, and that’s why you need point-of-use filters. EXAIR Automatic Drain Filter Separators have 5 micron particulate elements, and centrifugal elements that ‘spin’ any moisture out. If oil is an issue, our Oil Removal Filters have coalescing elements for oil/oil vapor removal, and they provide additional particulate protection to 0.03 microns.
  • Pressure control. Your compressor’s discharge pressure needs to be high enough to operate your pneumatic device(s) with the highest pressure demand. Odds are, though, that not everything in your plant needs to be operated at that pressure. EXAIR Pressure Regulators are a quick & easy way to ‘dial in’ the precise supply pressure needed for specific products so they can get the job done, without wasting compressed air.
  • Storage. This could also be considered system “stuff”, but I’m including it under point-of-use because that’s oftentimes the reason for intermediate storage. Having a ready supply of compressed air near an intermittent and/or large consumption device can ensure proper operation of that device, as well as others in the system that might be “robbed” when that device is actuated. They’re good for the system, too, as they can eliminate the need for higher header pressures, which cause higher operating costs, and increased potential for leaks. EXAIR Model 9500-60 60 Gallon Receiver Tanks are an ideal solution for these situations.

For more information on proper installation and use of compressed air system “stuff” like this, the Compressed Air & Gas Institute’s Compressed Air and Gas Handbook has a good deal of detailed information. The Air Data section of EXAIR’s own Knowledge Base is a great resource as well.

Of course, all the attention you can pay to efficiency on the supply side doesn’t matter near as much if you’re not paying attention to HOW you’re using your compressed air. EXAIR Intelligent Compressed Air Products are designed with efficiency, safety, and noise reduction in mind. Among the other ways my fellow Application Engineers and I can help you get the most out of your compressed air system, we’re also here to make sure you get the right products for your job. To find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Intelligent Compressed Air: Refrigerant Dryers

Published on by Tyler DanielLeave a comment

When we talk with customers about their EXAIR Products, we also discuss the quality of their compressed air. Many of our products have no moving parts and are considered maintenance-free when supplied with clean, moisture free compressed air. One of the most critical aspects of a compressed air distribution system is the dryer.

No matter where you are in the world, the atmospheric air will contain water vapor. Even in the driest place in the world, McMurdo Dry Valley in Antarctica, there is some moisture in the air. As this air cools to the saturation point, also known as dew point, the vapor will condense into liquid water. The amount of this moisture will vary depending on both the ambient temperature and the relative humidity. According to the Compressed Air Challenge, a general rule of thumb is that the amount of moisture air can hold at a saturated condition will double for every increase of 20°F. In regions or periods of warmer temperatures, this poses an even greater problem. Some problems that can be associated with moisture-laden compressed air include:

  • Increased wear of moving parts due to removal of lubrication
  • Formation of rust in piping and equipment
  • Can affect the color, adherence, and finish of paint that is applied using compressed air
  • Jeopardizes processes that are dependent upon pneumatic controls. A malfunction due to rust, scale, or clogged orifices can damage product or cause costly shutdowns
  • In colder temperatures, the moisture can freeze in the control lines

In order to remove moisture from the air after compression, a dryer must be installed at the outlet of the compressor. It is recommended to dry the compressed air to a dew point at least 18°F below the lowest ambient temperature to which the distribution system or end use is exposed. A dew point of 35-38°F is often sufficient and can be achieved by a refrigerated dryer (Best Practices for Compressed Air Systems). This makes the refrigerant dryer the most commonly used type in the industry.

A refrigerant dryer works by cooling the warm air that comes out of the compressor to 35-40°F. As the temperature decreases, moisture condenses and is removed from the compressed air supply. It’s then reheated to around ambient air temperatures (this helps to prevent condensation on the outside of distribution piping) and sent out to the distribution system.

With your air clean and dry at the point of use, you’re making sure you get the most out of EXAIR’s Intelligent Compressed Air Products without adhering to pesky maintenance procedures.

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

Compressor image courtesy of Tampere Hacklab via Flickr Creative Commons License