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.

Bellows

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
Email: johnball@exair.com
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.

3 Common Mistakes in Your Compressed Air System

Every day I speak with engineers who are having trouble using compressed air products. A common problem they have is not providing an adequate air supply to their unit. I go through a basic troubleshooting technique to ensure that their pressure and flow rate is adequate. I ask them to install tee on the inlet to the compressed air product in order to install a pressure gauge right at the inlet to the pipe. This allows us to know exactly what pressure we are supplying to the product. Customers are always surprised how the gauge on the compressor or the regulator may read 120 PSIG, but the gage on the inlet to the compressed air product is significantly less.

Last year, my colleague, Russell Bowman, made an excellent video showing how the inlet pressure at the knife will have a significant impact on the performance of the Super Air Knife.  In the video, he changes the length and ID of the compressed air supply to illustrate the difference a proper supply line will have on the performance of a compressed air products.

Not providing adequate air supply is commonly caused by these three mistakes, when plumbing compressed air systems.

1. Incorrectly Sized Piping – This can be the single biggest problem. A lack of planning before installing a compressed air product. Not all compressed air systems are created equal. Though a 1/4″ shop air hose may work for a number our products, some of our products require a larger air line because they require more volume of air to be effective. We often speak with customers an illustrate this problem by stating small air lines are like trying to feed a fire hose with a garden hose – there simply is not enough volume to create the pressure necessary to reach the fire, or solve the application in our scenarios. We publish the flow rates for all of our products and make inlet pipe size recommendation in the installation and maintenance guide furnish with the products so you may avoid this common problem. We also have air data tables in our Knowledge Base or  you may consult an application engineer who will be happy to make the proper recommendation.

2. Quick Disconnects – These handy connectors are great when operating a brad nailer, or a small blow gun, but the small through diameter can severely limit the flow rate into a long air knife, large diameter air operated conveyor, or big vortex tubes.  Due to this fact it is strongly advised to use threaded fittings or over-sized quick disconnects.

3. Adding extra hose or pipe – Extra hose is never a bad thing, right? No, an extra 30 feet of air hose can significantly drop the pressure of a compressed air system. 20 feet of ½ Pipe can flow 70 CFM with a 5 PSI pressure drop.  50 feet of ½” pipe will only flow 42 SCFM with the same 5 PSIG pressure drop. Keep your hose or pipe lengths to a minimum to improve the volume of air you can deliver to a compressed air product.

Dave Woerner
Application Engineer
DaveWoerner@EXAIR.com
@EXAIR_DW

Air Amplifier Provides Cooling for HOT Parts

Hot Cylinders

The five C’s of EXAIR products are Cooling, Cleaning, Conserving, Conveying, and Coating.  All EXAIR products are suitable for applications in these areas, with varying degree of possibility.  When it comes to cooling, one of the most suitable EXAIR products is the Super Air Amplifier.

An Air Amplifier can increase the volume of ambient air directed over an specific area, effectively decreasing the cooling time needed in an application.  Air Amplifiers cool effectively due to the fundamental principles of convective heat transfer.  In convective heat transfer, cooling capacity can be increased by increasing the temperature differential between the cooling medium and the object to be cooled, or by increasing the flow of the cooling medium.

An Air Amplifier is the best cooling choice when the material to be cooled is at an extremely high temperature.  For example, in the application above, 903°C (1650°F) cylinders need to be cooled to ambient temperature as quickly as possible. Vortex Tubes are another product our customers consider for cooling applications. Vortex Tubes are the best choice when the area to be cooled is small and the temperature differential is not as large. A Vortex Tube based solution will provide very cold air, but at a lower air flow over a small area and they were not the best choice for the application in the image above.

In the same application, a Super Air Amplifier can provide large volumes of ambient air over a large area, effectively cooling the cylinders much more efficiently.  The cooling can be achieved in less time, and with maximum efficiency of compressed air implementation. Air Amplifiers also offer great benefits over electric fans in this rough environment: they can withstand higher temperatures and there are no moving parts to wear or break.

If you have an application in need of efficient cooling, contact an EXAIR Application Engineer to find out if an Air Amplifier will work for you.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Air Pressure Loss

Loss of air pressure scenario:

  1. Customer calls in because she is not pleased with the performance of her new 12″ Super Air Knife. Customer states something like “this thing couldn’t spread the seeds of a dandelion”.
  2. EXAIR does not take umbrage to the statement, we begin to troubleshoot the situation. We generally begin by trying to determine the line pressure of her compressed air system; “What is your line pressure?”
  3. Customer states 95 PSIG line pressure, and potentially utters something else about being a monkeys uncle if this Super Air Knife is not broken.
  4. EXAIR reassures the customer that the Super Air Knife is most likely functioning properly – BUT – being starved for air. We typically ask if she knows what pressure is running through the knife?
  5. Customer thinks since there is 95 PSIG on the main supply, the Super Air Knife must also be at 95 PSIG.
  6. We ask what size air line is feeding the knife, because we know there can be a significant pressure loss due to improperly (small) sized air lines.
  7. Customer states 1/4″ air line and push to lock fittings.
  8. We state that the air line is much too small for delivering the proper amount of compressed air and the result is a pressure loss, the knife is fine but not geting enough air volume to do any work. We recommend the proper sized air lines, further assure the customer this will take care of the problem and let them know we are available if they still cannot get the Super Air Knife to work.
  9. More times than not, customer does not call back.
  10. Sometimes they call back and let us know that we could spread the seeds of a dandelion, it’s working great now, and thanks again.

If air lines or fittings are too small they cannot deliver the volume necessary to maintain pressure. Compressors sitting on one end of the plant and feeding equipment on the other end will experience pressure losses due to friction in the air lines, resulting in lower pressure in the far end of the plant compared to the closer end.

It is important to measure pressure at various places and points in your compressed air system in order gage your pressure and even diagnose some equipment.

  1. Measure your pressure right at the compressor discharge. This will give you a good baseline of what you should expect.
  2. If you have any additional dryers or treatment equipment you should also measure pressure after this equipment.
  3. Measure your pressure after each filter in the system. A large pressure loss after a filter will indicate a clogged filter and that it is time to change it out.
  4. If you have installed a primary receiver tank, measure the pressure at the outlet. Since the plant will use its compressed air from out of the receiver, a pressure loss here will indicate high demands periods or the need for a larger receiver.
  5. Measure pressure at the end of long headers. This reading will reveal any pressure losses due to friction loss over long distances. It can also indicate the need for larger diameter headers.
  6. Lastly, measure pressure before a filter/regulator at an end use application, also measure pressure right at the inlet of the end use product. This is the example for the Super Air Knife above. A pipe tee on the Super Air Knife inlet with a pressure gauge in the open leg of the tee would have indicated a large pressure loss when compared to the pressure at the filter/regulator. This is a clear sign of undersized compressed air feed lines.

If you have any questions for us along the way, please let us know.

Kirk Edwards
Application Engineer
kirkedwards@exair.com