Compressor Intake – Air Flows 

Flow rate is the quantity of material that is moved per unit of time.  Generally, the quantity of material can be expressed as a mass or a volume.  For example, mass flow rates are in units of pounds per minute or kilograms per hour.  Volumetric flow rates are stated in cubic feet per minute, CFM, or liters per hour, LPH.  The trick begins when volumetric flow rates are used with compressible gases.  In this blog, I will go over the various acronyms and the reasons behind them.

What acronyms will be covered?

CFM – Cubic Feet per Minute

SCFM – Standard Cubic Feet per Minute

ACFM – Actual Cubic Feet per Minute

ICFM – Inlet Cubic Feet per Minute

The volumetric component of the flow rate is CFM or Cubic Feet per Minute.  This term is commonly used for rating air compressors.  From the history of air compressors, they could calculate the volume of air being drawn into the air compressor by the size of the cylinder.  With the volume of the compression chamber and the rotations per minute of the motor, RPM, they could calculate the volumetric air flows.  As conditions change like altitude, temperature, and relative humidity, the volumetric value of CFM changes.  To better clarify these conditions, compressor manufacturers have decided to add terms with a definition.  (For your information, air compressors still use CFM as a unit of air flow, but now this is defined at standard temperature and pressure).

The first letter in front of CFM above now defines the conditions in which volumetric air flow is being measured.  This is important for comparing pneumatic components or for properly sizing pneumatic systems.  Volume is measured within three areas; temperature, pressure, and relative humidity.  We can see this in the Ideal Gas Law, reference Equation 1.

Equation 1:

P * V = n * R * T

Where:

P – Absolute Pressure

V – Volume

n – Number of molecules of gas

R – Universal Gas Constant

T – Absolute Temperature

The volume of air can change in reference to pressure, temperature, and the number of molecules.  You may ask where the relative humidity is?  This would be referenced in the “n” term.  The more water vapor, or higher RH values, the less molecules of air are in a given volume.

SCFM is the most commonly used term, and it can be the most confusing.  The idea behind this volumetric air flow is to set a reference point for comparisons.  So, no matter the pressure, temperature, or relative humidity; the volumetric air flows can be compared to each other at that reference point.  There have been many debates about an appropriate standard temperature and pressure, or STP.  But as long as you use the same reference point, then you can still compare the results.  In this blog, I will be using the Compressed Air and Gas Institute, CAGI, reference where the “Standard” condition is at 14.5 PSIA, 68 o F, and 0% RH.  Since we have a reference point, we still need to know the actual conditions for comparison.  It is like having the location of a restaurant as a reference, but if you do not know your current location, you cannot move toward it.   Similarly, we are “moving” the air from its actual condition to a reference or “Standard” condition.  If we do not know the actual state where the air began, then we cannot “move” toward that reference point.  We will talk more about this later in this blog.

ACFM is the volumetric air flow under actual conditions.  This is actually the “true” flow rate.  Even though this term is hardly used, there are reasons why we will need to know this value.  We can size an air compressor that is not at “Standard” conditions, and we can use this value to calculate velocity and pressure drop in a pneumatic system.  We can correlate between SCFM and ACFM with Equation 2.

Equation 2:

ACFM = SCFM * [Pstd / (Pact – Psat * Φ)] * (Tact / Tstd)

Where:

ACFM – Actual Cubic Feet per Minute

SCFM – Standard Cubic Feet per Minute

Pstd – standard absolute air pressure (PSIA)

Pact – absolute pressure at the actual level (PSIA)

Psat – saturation pressure at the actual temperature (PSI)

Φ – Actual relative humidity (%)

Tact – Actual ambient air temperature (oR)

Tstd – Standard temperature (oR)

ICFM is one of the newest terms in the history of air compressors.  This is where devices are added to the inlet of an air compressor, affecting flow conditions.  If you have a blower on the inlet of an air compressor, the volumetric flow rate changes as the pressure and temperature rises at the “Inlet”.  If a filter is used, then the pressure drop will decrease the incoming pressure at the “Inlet”.  These devices that affect the volumetric flow rate for an air compressor should be considered.  The equation to relate ACFM to ICFM is Equation 3.

Equation 3:

ICFM = ACFM * (Pact / Pf) * (Tf / Tact)

Where:

ICFM – Inlet Cubic Feet Per Minute

ACFM – Actual Cubic Feet per Minute

Pact – absolute pressure at the actual level (PSIA)

Pf – Pressure after filter or inlet equipment (PSIA)

Tact – Actual ambient air temperature (oR)

Tf – Temperature after filter or inlet equipment (°R)

To expand on my explanation above about SCFM and ACFM, a technical question is asked often about the pressure when using SCFM.  The reference point of 14.5 PSIA is in the definition of the term for SCFM.  Remember, this is only a reference point.  The starting location is also needed as it gives us the ACFM value where the air values are true and actual.  Then we can make a comparison of actual air usage. 

As an example, let’s look at two air nozzles that are rated at the same air flow; 60 SCFM.  The EXAIR Super Air Nozzle, model 1106, is cataloged at 60 SCFM at 80 PSIG, and a competitor is cataloged at 60 SCFM at 72 PSIG.  By comparison, they look like they use the same amount of compressed air, but actually they do not.  To simplify Equation 2, we can compare the two nozzles at the same temperature and RH at 68 oF and 0% RH respectively.  This equation can be reduced to form Equation 4.

Equation 4:

ACFM = SCFM * 14.5 / (P + 14.5)

@72 PSIG Competitor:

ACFM = 60 SCFM * 14.5 PSIA/ (72 PSIG + 14.5 PSIA)

= 10.1 ACFM

@80 PSIG EXAIR Super Air Nozzle:

ACFM = 60 SCFM * 14.5 PSIA / (80 PSIG + 14.5PSIA)

= 9.2 ACFM

Even though the SCFM is the same amount, you are actually using 10% more air with the competitive nozzle that was reported at 60 PSIG.  So, when it comes to rating pneumatic products, improving efficiency, and saving money; always determine the pressure that you are at.  The more you know about volumetric flow rates, the better decision that you can make.  If you need more information, you can always contact our Application Engineers at EXAIR.  We will be happy to assist.

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

Photo: Compressor equipment by terimakasih0Pixabay license

Focusing to be a Good Corporate Steward

Every April, EXAIR takes the time to revisit our sustainability plan and the responsibility we have to be good stewards of our resources and to minimize our impact on the environment. It remains interesting how intertwined our internal processes are with the world around us, and we like to pay attention to this.

We realize that what we do as a company can directly impact others and our environment. We have reduced our consumption of resources, increased our recycling efforts and incorporated practices and standards into our product development, manufacturing and fulfillment processes that are beneficial to the environment. Our action plan significantly improves our operations, practices, facility and products. Here are some of the steps we’ve taken:

Compressed Air

  • Consumption reduced through a leak detection and mitigation program that saved one million cubic feet of compressed air per year.
  • Utilizing our own engineered compressed air nozzles throughout the plant minimizes compressed air use compared to commercial nozzles.

Metals

  • We recycle 100% of the metal scrap from our machining processes. The materials we recycle are aluminum, Type 303 and Type 316 stainless steel. 

Electrical Power

  • Our VSD (variable speed drive) air compressor reduced our electrical consumption by over 4,500 kWh in the past year compared to a conventional air compressor.
  • Consumption reduced through increased use of natural light, higher efficiency fluorescent fixtures and LED technology.
  • EXAIR continues to make improvements to the efficiency of our computers and computer servers which require fewer Kilowatt hours (KWH) per day.

Fossil Fuels

  • EXAIR delivers 91% of our invoices electronically which has eliminated those traditional postal service mailed copies.
  • We focus on local and regional vendors whenever possible, which reduces delivery distances and fuel.

       Paper/Cardboard

  • Electronic delivery of invoices allowed 67% reduction in printed pages.
  • Most shipments use recycled Kraft paper with a perfect “green score” of 360.
  • Recycled 100% of our cardboard and mixed paper products. Of the waste we place into our trash dumpsters – 80% is recycled and 20% is sent to the landfill.
  • Over the past year, EXAIR recycled 416 cubic yards of paper and cardboard.

Fresh Water

  • We use our very own Chip Trapper Systems in our manufacturing areas to extend the water-soluble coolant life from 6 weeks per changeover to 6 months per changeover. Keeping our coolant clean allows us to minimize the total amount of wastewater we recycle each year.
  • Our wastewater is 100% recycled

Natural Gas

  • Consumption reduced by installing programmable thermostats wherever possible to match heating/cooling cycles with facility usage patterns.

Through an expanded recycling program, we are able to 100% recycle our metal scrap, paper and cardboard, wastewater, wood and plastics.

The impact our products make is also notable:

  • EXAIR blow off products designed specifically to reduce compressed air consumption energy usage
  • A new tool developed as part of our coolant management system now available to customers
  • Packaging materials used by EXAIR are fully recyclable
  • Most EXAIR products themselves are largely or fully recyclable at the end of their useful lives
  • RoHS compliance on applicable products insures that, should these products end up in a landfill at the end of their useful lives, they will not contaminate the environment with unacceptable levels of lead, mercury, hexavalent chromium, PBB, PBDE or cadmium.

We will remain focused on our impact and make improvements through new materials, products, processes and technologies when we have the opportunity for continued improvement.

Enjoy today, the day where we recognize how precious the planet is. Join EXAIR and some of the largest and most notable companies on earth by practicing some of these improvements and using EXAIR Intelligent Compressed Air® products.

Sincerely,
The EXAIR Team
www.EXAIR.com

Proper Labeling of Piping Systems Increases Safety

Industrial facilities can have a multitude of piping and utilities within them. Some of the piping can all look similar, especially if it is not labeled. water, sprinkler lines, compressed air, even steam, and refrigeration lines are just a few of those that can easily be seen within a number of manufacturing facilities. Proper labeling of these helps to ensure plant safety and can also lead to higher efficiencies within the system.

Properly labeled compressed air piping.

So how does labeling lead to safety? Well, in more than one occurrence I have been inside of facilities where piping that was not intended for compressed air, such as PVC was used for it. When the incorrect piping gets used it can become easily confused and if the contractor that is installing new equipment doesn’t do their homework then it can lead to catastrophic errors. For instance, piping can rupture, or even worse, you could easily pipe the incorrect utility into a piece of equipment. Imagine seeing PVC pipe, which is used for water, and hooking it to a rinse application only to find someone improperly used the piping for industrial compressed air. Or vise versa, an unlabeled pipe thought to be compressed air is actually city water and the next thing happening is water raining down on a packaging blowoff.

Cold Water Piping Labeled properly.

This all can and should be easily prevented by properly labeling any and all piping systems thoroughly throughout the facility. This not only names the utility but generally shows the flow direction as well which an help determine where the source is coming from as well. When performing the first step in the 6 Steps To Compressed Air Optimization knowing the direction of flow is critical when installing a Digital Flowmeter in order to assess system efficiency for compressed air.

The proper labeling and utilizing proper piping within industrial environments can easily prevent accidents and ensure ease of troubleshooting or new installations because the piping is already labeled. If you would like to discuss more on what types of piping are acceptable to use with compressed air, feel free to contact an Application Engineer.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Video Blog: How-to Install EXAIR’s Hot Tap Digital Flowmeters

The Hot Tap Digital Flowmeters can be installed on pressurized compressed air systems and pipes. This avoids the downtime necessary to depressurize the compressed air system and keeps your processes up and running.

Watch the video below to learn how simple it is to install EXAIR’s Hot Tap Digital Flowmeters.

Jordan Shouse
Application Engineer

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