Air: What is it?

Air Balloons

What is Air? Air is an invisible gas that supports life on earth. Dry air is made from a mixture of 78% Nitrogen, 21% Oxygen, and 1% of remaining gases like carbon dioxide and other inert gases.  Ambient air contains an average of 1% water vapor, and it has a density of 0.0749 Lbs./cubic foot (1.22 Kg/cubic meter) at standard conditions.  Air that surrounds us does not have a smell, color, or taste, but it is considered a fluid as it follows the rules of fluid dynamics. But unlike liquids, gases like air are compressible.  Once we discovered the potential of compressing the surrounding air, we were able to advance many technologies.


Guess when the earliest air compressor was used?  Believe it or not, it was when we started to breathe air.  Our diaphragms are like compressors.  It pulls and pushes the air in and out of our lungs.  We can generate up to 1.2 PSI (80 mbar) of air pressure.  During the iron age, hotter fires were required for smelting.  Around 1500 B.C., a new type of air compressor was created, called a bellows.  You probably seen them hanging by the fireplaces.  It is a hand-held device with a flexible bag that you squeeze together to compress the air.  The high stream of air was able to get higher temperature fires to melt metals.

Then we started to move into the industrial era.  Air compressors were used in mining industries to move air into deep caverns and shafts.  Then as the manufacturing technologies advanced, the requirements for higher air pressures were needed.  The stored energy created by compressing the air allowed us to develop better pneumatic systems for manufacturing, automation, and construction.  I do not know what the future holds in compressed air systems, but I am excited to find out.

Since air is a gas, it will follow the basic rules of the ideal gas law;

PV = nRT  (Equation 1)

P – Pressure

V – Volume

n – Amount of gas in moles

R – Universal Gas Constant

T – Temperature

If we express the equation in an isothermal process (same temperature), we can see how the volume and pressure are related.  The equation for two different states of a gas can be written as follows:

P1 * V1 = P2 * V2  (Equation 2)

P1 – Pressure at initial state 1

V1 – Volume at initial state 1

P2 – Pressure at changed state 2

V2 – Volume at changed state 2

If we solve for P2, we have:

P2 = (P1 * V1)/V2  (Equation 3)

In looking at Equation 3, if the volume, V2, gets smaller, the pressure, P2, gets higher.  This is the idea behind how air compressors work.  They decrease the volume inside a chamber to increase the pressure of the air.  Most industrial compressors will compress the air to about 125 PSI (8.5 bar).  A PSI is a pound of force over a square inch.  For metric pressure, a bar is a kg of force over a square centimeter.  So, at 125 PSI, there will be 125 pounds of force over a 1” X 1” square.  This amount of potential energy is very useful to do work for pneumatic equipment.  To simplify the system, the air gets compressed, stored as energy, released as work and is ready to be used again in the cycle.

Air Compressor

Compressed air is a clean utility that is used in many different applications.  It is much safer than electrical or hydraulic systems.  Since air is all around us, it is an abundant commodity for air compressors to use.  But because of the compressibility factor of air, much energy is required to create enough pressure in a typical system.  It takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet of air (113L) to 125 PSI (8.5 bar) every minute.  With almost every manufacturing plant in the world utilizing compressed air in one form or another, the amount of energy used to compress air is extraordinary.  So, utilizing compressed air as efficiently as possible is mandatory.  Air is free, but making compressed air is expensive

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Products, you can contact an Application Engineer at EXAIR.

John Ball
Application Engineer
Twitter: @EXAIR_jb


Picture: Hot Air Rises by Paul VanDerWerf. Creative Commons Attribution 2.0 Generic.

Picture: Bellows by Joanna Bourne. Creative Commons Attribution 2.0 Generic.

Picture: Air Compressor by Chris Bartle. Creative Commons Attribution 2.0 Generic.

Intelligent Compressed Air: Membrane Dryers – What are they and How Do they Work?

Recently we have blogged about Compressed Air Dryers and the different types of systems.  We have reviewed the Desiccant and Refrigerant types of dryers, and today I will discuss the basics of  the Membrane type of dryers.

All atmospheric air that a compressed air system takes in contains water vapor, which is naturally present in the air.  At 75°F and 75% relative humidity, 20 gallons of water will enter a typical 25 hp compressor in a 24 hour period of operation.  When the the air is compressed, the water becomes concentrated and because the air is heated due to the compression, the water remains in vapor form.  Warmer air is able to hold more water vapor, and generally an increase in temperature of 20°F results in a doubling of amount of moisture the air can hold. The problem is that further downstream in the system, the air cools, and the vapor begins to condense into water droplets. To avoid this issue, a dryer is used.

Membrane Dryers are the newest type of compressed air dryer. Membranes are commonly used to separate gases, such as removing nitrogen from air. The membrane consists of a group of hollow fiber tubes.  The tubes are designed so that water vapor will permeate and pass through the membrane walls faster than the air.  The dry air continues on through the tubes and discharges into the downstream air system. A small amount of ‘sweep’ air is taken from the dry air to purge and remove the water vapor from inside the dryer that has passed through the membrane tubes.

Membrane Dryer
Typical Membrane Dryer Arrangement

Resultant dew points of 40°F are typical, and dew points down to -40°F are possible but require the use of more purge air, resulting in less final dry compressed air discharging to the system.

The typical advantages of Membrane Dryers are-

  1.  Low installation and operating costs
  2.  Can be installed outdoors
  3.  Can be used in hazardous locations
  4.  No moving parts

There are a few disadvantages to consider-

  1. Limited to low capacity systems
  2. High purge air losses (as high as 15-20% to achieve lowest pressure dew points
  3. Membrane can be fouled by lubricants and other contaminants, a coalescing type filter is required before the membrane dryer.

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
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Twitter: @EXAIR_BB


Membrane Dryer Schematic – From Compressed Air Challenge, Best Practices for Compressed Air Systems, Second Edition




Intelligent Compressed Air: How to Develop a Pressure Profile

An important part of operating and maintaining a compressed air system is taking accurate pressure measurements at various points in the compressed air distribution system, and establishing a baseline and monitoring with data logging.  A Pressure Profile is a useful tool to understand and analyze the compressed air system and how it is functioning.

Pressure Profile 1
Sample Pressure Profile

The profile is generated by taking pressure measurements at the various key locations in the system.  The graph begins with the compressor and its range of operating pressures, and continues through the system down to the regulated points of use, such as Air Knives or Safety Air Guns.  It is important to take the measurements simultaneously to get the most accurate data, and typically, the most valuable data is collected during peak usage periods.

By reviewing the Pressure Profile, the areas of greatest drop can be determined and the impact on any potential low pressure issues at the point of use.  As the above example shows, to get a reliable 75 PSIG supply pressure for a device or tool, 105-115 PSIG must be generated, (30-40 PSIG above the required point of use pressure.)  As a rule of thumb, for every 10 PSIG of compressed air generation increase the energy costs increase 5-7.5%

By developing a total understanding of the compressed air system, including the use of tools such as the Pressure Profile, steps to best maximize the performance while reducing costs can be performed.

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

Glass Filled PEEK Super Air Knife w/ Brass Hardware & PTFE Shim? No Problem!

That’s right folks, we’ve gone and done it again.  When a customer calls for custom product because their environment calls for it or due to dimensional requirements, EXAIR has the ability and flexibility to meet those needs!

This time around it was a customer with specific material requirements due to their environment. I had a customer contact me recently that was using an aluminum Super Air Knife near a high voltage operation and was getting ground interference due to the aluminum air knife.  They asked if it was possible to make them a custom knife out of PEEK plastic.  After some light discussions about the form of the knife and what other materials are safe for their environment we settled on a 30% glass filled PEEK plastic for the knife, brass bolts and pipe plugs, with a PTFE shim installed.   The form factor of the knife would follow the same shape as our PVDF Super Air Knives that are available from stock.   The customer could not use PVDF due to high temperature and potential off-gassing in the process.

The results are shown below.

EXAIR 6″ Super Air Knife in 30% Glass Filled PEEK Plastic w/ Brass Hardware and PTFE Shim
End View – 6″ Super Air Knife in 30% Glass Filled PEEK Plastic w/ Brass Hardware & PTFE Shim

Whether you are looking for a one off product that is tailor made to your application or want to have a simple feature like hardware material changed in a stock EXAIR product that you are incorporating into thousands of machines, we have the solution for you.

Brian Farno
Application Engineer Manager





Compressed Air – Diagnose a Car Problem or Simulate Ape Breath

At the end of this week and all through next week, I will be taking my family to the “most magical place on earth!”  Keep in mind, I have three daughters at the ages of 5 (almost 6 if you ask her), 3, and 1. (Not to mention my wife who has spent endless hours researching and scheduling our events for the week.) It’s not just my household that is going on this trip though, it is my entire family, parents, siblings, teenage nieces, and one nephew.   I honestly don’t remember the last family vacation we went on with all of us there so it is going to be an amazing experience no matter what.

Cincinnati to Orlando = 13 hours (not with kids)

The trip from Cincinnati, OH to Orlando, FL is approximately 13 hours, factor in the children and parents ages and I am going to go ahead and say we are looking at 24 hours of travel, at least.   Now I am being smart, we are breaking this trip up into two days. I envision something that will look like a military convoy going down I-75 when the 3 vehicles all get going, the painful truth is it will look more like the Clampets move to Hollywood.

In preparation for the trip I have been doing some routine maintenance on our family van and discovered what I believed to be a rather bad coolant leak.  Now, I didn’t see the leak but I noticed the lack of coolant in the system.   So I started to conduct a few tests and oddly enough, they involved compressed air.   First I filled the system and pulled a vacuum on the entire cooling system to draw out any air.   Once I pulled around 11″ of mercury, I went ahead and turned off my compressed air vacuum generator and tried to see if it would lose vacuum.  It didn’t, so I then hooked a hose to a container of coolant and slowly released the vacuum sucking the coolant down into the system and eliminating the risk of air bubbles.

Since I couldn’t see a loss in vacuum I decided I would test the system under pressure.  To do this I simply removed the radiator cap and attached a special tool which would pump air down into the radiator and put the entire system under pressure, much like it would be during normal operation.  Once I built the pressure up to 15 psig, the factory cap was rated for 16 psig,  I let it sit.  I scoured every single coolant line I could find and came up dry.  Couldn’t find a single drop of coolant escaping the system at all and it even held pressure for a solid hour. Coming up with no leak I decided to give it a test drive and low and behold, I have yet to find a leak.  My only theory at this point is during some warranty work a dealership must have disconnected a hose and forgot to fill it back up, or it is normal evaporation seeing as how I don’t remember the last time I topped off the coolant.

The entire time I was troubleshooting this system I found it interesting I was still using compressed air in some form, even on a liquid cooling system.  I then started to wonder if I am going to be able to see any EXAIR products while at that magical park in Orlando, hopefully something like the Roaring Banana Breath that is featured in our Super Air Amplifiers section of the catalog. Our amplifiers also get used to puff air at folks during other “4D” experiences throughout the world.

EXAIR Super Air Amplifiers help disperse banana scents into the air and into the face of patrons at a theme park ride.

Nonetheless, compressed air helped me determine that my family’s vehicle is not going to be spraying coolant on the roadway during this trip and I am glad for it.

Brian Farno
Application Engineer Manager


There’s More Than 1 Way To Blow Some Air

Just today I spoke with a customer who is threading the ends of pipes and needs to blow the coolant and chips out of the threads.   The pipes range from 4″ to 9 – 5/8″ Diameters.  They are all threaded then fed into a trough and pushed down line to the next operation.

A machine with an out-feed roller conveyor similar to the pipe threading machine mentioned.

The photo above is not the exact machine but you can see where if this was used to process piping the different diameter pipes would all sit at the same level.  One option could be to use a Super Air Wipe  for this application but then the smaller diameters would not pass through the center of the Air Wipe, instead they would pass through the bottom half of the airflow which may not give optimal performance. Instead, I suggested to use 4 of our 6″ Super Air Knife kits and 2 of our Electronic Flow Control units.


2 - 110006 - 6" Aluminum Super Air Knives coupled together w/  a 110900 SAK Connector Kit
2 – 110006 – 6″ Aluminum Super Air Knives coupled together w/ a 110900 SAK Connector Kit

I  suggested that we make two pairs of knives for this blowoff setup by coupling two of the 6″ Super Air Knives together.  Once they are coupled together like is shown above, we could mount the two coupled air knives vertically along the trough and blowing at a 45° angle toward the center of the conveyor.  The plumbing of the two bottom knives will be to one EFC while the top two knives will be plumbed to the other.    The sensors will then be set up at two different heights, lower knives to sense the bottom of the pipe and the upper knife sensor will be set just above the bottom 6″ knife.

The reason for using 4 – 6″ Super Air Knives and 2 EFCs instead of 2 – 12″ Super Air Knives and 1 EFC is to save the most compressed air possible.   By enabling them to turn the top two 6″ Super Air Knives off automatically when they are running below a 6″ diameter pipe.  Then when a larger pipe is processed the top knives will also kick on with the lower knives and provide a uniform blowoff of the product.

So if you have multiple sizes of product being processed on the same line and don’t think any one solution will work, contact us and see if we can’t come up with our own recipe.

Brian Farno
Application Engineer


Machine image courtesy PEO ACWA Creative Commons


Need More Capacity? Start By Finding it in House or Renting

I field a decent number of calls from companies that are trying to expand to new lines or venture into an area of production that they have not crossed into before.  Maybe it is bringing a process in-house that they traditionally outsourced, or altering a process that now requires a large scale blow off operation. In many cases, as these companies grow and succeed, their compressed air systems grow with them. Some of them need to find out find out how much air they will need if when they make decisions to bring processes in house or expand a current process.

One of the first options when needing more capacity from your current compressed air system is to take a look at the existing demand side and determine if we can free up enough supply to meet the requirements of this new option.   Let’s say for instance a new 60″ Super Air Knife is needed.   To test that unit at 80 psig inlet pressure we would need to free up 174 SCFM of compressed air. In all the years we have been around it is still surprising to consult with customers who are using large numbers of open blow-offs, homemade air knives, coolant hoses and nozzles for compressed air etc. These companies can find that extra capacity in their current systems by retrofitting engineered solutions on to the aforementioned poor solutions for keeping compressed air efficient. IF you are using some of those solutions, call EXAIR today to find out how much air our products may save you.

In the event that is not possible to find the necessary new volume of compressed air by streamlining your current system, it means looking at adding compressor capacity.  Some companies think they have to go out to buy a new compressor immediately, simply to test this new process.   That is more often than not, false.   The best recommendation I have is to look into renting a compressor, much like the one shown below.

A Rental Tow Behind Air Compressor
A Rental Tow Behind Air Compressor
The compressor distribution piping.
The compressor distribution piping.

I saw this unit while I was jogging, well attempting to jog, on my lunch break.  This was outside a local company that apparently, going through a very similar scenario like I mentioned above.  When I looked a little closer, I noticed the unit included around a 75-100′ of hose that did not use the dreaded quick disconnect fittings everyone sees.  Instead it utilized what I know as a Chicago style air fitting which does not restrict the air flow nearly as much as a quick disconnect and permits you to utilize the largest volume of compressed air from the compressor – remember folks: properly sized compressed air lines and fittings are extremely important when needing to keep volume and pressure of compressed air at high levels.

A Chicago Style Air Fitting
A Chicago Style Air Fitting


Once I looked up the statistics on the compressor I found that it will generate up to 375 CFM at 150 psig.  This is more than enough to test or run a 60″ Super Air Knife and validate whether additional compressors are needed, as well as if the Super Air Knife will perform to meet your needs.   Then, when you are done with the test, you can simply return the air compressor. Based on the results of this test, this could be another point to decide if you could save the needed air from your current system or if you would require a new compressor.

The EXAIR Guarantee
The EXAIR Guarantee

The moral that I am trying to instill in this blog is simple.  If you have a need for more compressed air to validate a new or improved process, don’t hesitate to think outside of your existing system. Where there is a will and a need, there is a way.  If it doesn’t work, take advantage of our 30 day unconditional trial.

Brian Farno
Application Engineer