The word “accessory” can come with some baggage… it’s become synonymous with “add-on” and “up-sell,” and cost-mindful consumers may see them as just another way for a slick salesperson to make an extra buck. And… More
CFM, ICFM, ACFM, SCFM: Why so many volumetric flow rates?
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 or liters per hour. The trick begins when volumetric flow rates are used for a compressible gas. 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 history of air compressors, they could calculate the volume of air being drawn into the air compressor by the size of 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 value of CFM changes. To better clarify these conditions, compressor manufacturers decided to add terms with 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 the volumetric air flow is being measured. This is important for comparing pneumatic components or for properly sizing pneumatic systems. Volume is measured with three areas: temperature, pressure, and relative humidity. We can see this in the Ideal Gas Law: P * V = n * R * T or Equation 1:
V = n * R * T / P
V – Volume
n – Number of molecules of gas
R – Universal Gas Constant
T – Absolute Temperature
P – Absolute Pressure
The volume of air can change in reference to pressure, temperature, and the number of molecules. Where is the relative humidity? This would be referenced in the “n” term. The more water vapor, or higher RH value, the less molecules of air is in a given volume.
SCFM is the most commonly used term, and it can be the most confusing. The idea of 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 deg. F, and 0% RH. Since we have a reference point, we still need to know the actual conditions for comparison. It is like having a location of a restaurant as a reference, but if you do not know your current location, you cannot reach it. Similarly, we are “moving” the air from its actual condition to a reference or “Standard” condition. We will need to know where the air began in order to reach 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 system. We can correlate between SCFM and ACFM with 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 the 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 the ACFM to ICFM is with Equation 3:
ICFM = ACFM * (Pact / Pf) * (Tf / Tact)
Where:
ICFM = Inlet Cubic Feet Per Minute
Pf = Pressure after filter or inlet equipment (PSIA)
Tf = Temperature after filter or inlet equipment (°R)
Examples of these different types of flow rates can be found here in this EXAIR blog by Tyler Daniel.
To expand on my explanation above about SCFM and ACFM, a technical question comes up about the pressure when using SCFM. The reference point of 14.5 PSIA is in the definition of SCFM. Remember, this is only a reference point. The starting location is actually required. This would be the ACFM value where the air values are true and actual. As an example, two air nozzles are rated for 60 SCFM. An EXAIR Super Air Nozzle, model 1106, is cataloged at 80 PSIG, and a competitor is cataloged at 60 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 Deg. F and 0% RH respectively. This equation can be reduced to Equation 4:
ACFM = SCFM * 14.5 / (P + 14.5)
@60 PSIG Competitor:
ACFM = 60 SCFM * 14.5 PSIA/ (60 PSIG + 14.5 PSIA)
= 11.7 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 21% more air with the competitive nozzle that was reported at 60 PSIG. So, when it comes to rating compressed air products or air compressors, always ask the conditions of pressure, temperature and RH. The more you know about volumetric flow rates, the better decision that you can make. If you need help, you can always contact our application engineers at EXAIR.
John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb
Compressor photo courtesy of David Pearcy via Creative Commons license.
Powerful and Safe Blowoffs with EXAIR’s Heavy Duty Safety Air Gun
EXAIR’s Heavy Duty Safety Air Gun is designed to provide powerful blasts of compressed air for use in rugged, industrial environments. With a larger 3/8 NPT air inlet compared to our other Safety Air Guns, it allows for higher force and flow values. It comes with a durable cast aluminum body and ergonomic composite rubber grip. The wide curved trigger allows for continuous use for hours without operator’s experiencing fatigue.
All of EXAIR’s Safety Air Guns come with an engineered compressed air nozzle at the tip. This allows you to remain OSHA compliant while still getting the force you need to get the job done. EXAIR’s Super Air Nozzles utilize the coanda effect to entrain large amounts of ambient air from the environment. This ambient air mixes with the primary airstream and is projected towards the target with more force and flow than the supplied compressed air could deliver alone.
Each of the Safety Air Guns is available with extensions fully assembled ranging from 6”-72”. You can simply add a “-“ and the required length, in inches, to the end of any Safety Air Gun Model number.
In addition, they’re also available with a Chip Shield to prevent any chips or debris from coming back into the faces of your operators. Effective chip guarding is another component of OSHA 1910.242(b) in addition to the concerns of dead-end pressure. To add a Chip Shield onto the gun as well, a “-CS” to the standard Model number. For example, a Model 1310-12-CS would be a 1310 gun with 12” extension and a Chip Shield installed. If the application involves blowing off metal chips or shavings, your operators will certainly appreciate this Chip Shield preventing the debris from blowing back all over them.
With EXAIR’s Heavy Duty Safety Air Gun, you can still achieve the high forces required for tough applications without the risk of injuries to personnel. It’ll also keep you safe from any fines associated with an unannounced OSHA visit. Do yourselves and your operators a favor and get one on order today!
Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD
Where Has The VariBlast Compact Safety Air Gun Been All My Life?!?
Have you ever happened across something that would have been a real “game changer” at some time in the past? I’ll never forget the time that I went camping with my sons’ Boy Scout Troop, and I was introduced to the peanut butter and bacon sandwich. I still enjoy one from time to time, but my doctor does not enjoy hearing about it…
I’ve also written before (and before) about when I found out EXAIR Vortex Tubes were being used in some shipyards for freeze sealing pipes…a task that (when I worked in a shipyard) we used tanks of liquid nitrogen for. I was amazed that such a cumbersome ordeal was replaced by something so simple and easy.
When we were developing the VariBlast Compact Safety Air Gun, a key feature…the variable flow trigger…also would have been real handy at a time in my not-so-distant past. See, I used to run a small industrial equipment service department, and one time I found myself in a pinch to get a structural steel tube frame made for a support for a particular piece of equipment. This wasn’t something we did all the time, and this particular job was a bit larger scale than most of what we’d done before. It wasn’t really a big deal; I just had to cut some rectangular tubing to length with our band saw, drill some small holes (for bolts) and bore some larger holes (for cables & hose) along the length.
We had a small air compressor and a cheap commercial grade air gun, which served the purpose of our infrequent usage. Blowing the shavings away from those holes, and the inside of the tubing was a challenge…that air gun would just barely move them all the way from the holes near the middle, and when I blew out the holes near the ends, the spray of coolant-soaked shavings was making a heck of a mess in our relatively small shop. After a while, I found that I could kind of “mash” the trigger a little to one side and get a rough measure of control…I was only going to have to mop about half the floor, instead of the whole thing, and I wasn’t going to have to wash the service truck parked in the closest garage bay to the shop area.
Needless to say, this wasn’t exactly ergonomic, and it was real pain (literally) to use my left hand for a few days following. Which, being left-handed, was kind of a drag.
Fast forward to just last year, when we rolled out the latest and greatest (in a distinguished line of latest and greatest) EXAIR product: the VariBlast Compact Safety Air Gun. Now, individually, the key features might not be all that mind-blowing to the casual observer, but taken together, they’re a pretty big deal. Consider:
*Aluminum construction – lightweight, durable, corrosion resistant.
*Two compressed air inlets – one on the bottom (below your pinkie finger) and one on the rear (above your thumb;) your choice…whichever makes your task easier.
*Cast-in hanger – to keep it out of the way, but still handy, when you’re not using it.
*Chip Shield – you still have to wear safety glasses, but this will keep them cleaner.
*Wide selection of engineered nozzles – from our Atto Super Air Nozzle (2.5 SCFM; 2.0 oz force) to the 1″ High Power Flat Super Air Nozzle (17.5 SCFM; 16 oz force,) there are 20 distinct models in stock. We can customize the performance of the VariBlast Compact Safety Air Gun to the specific needs of your intended use for it.
*Extensions – for applications that require a little (or a little more) reach, we offer the VariBlast Compact Safety Air Gun with rigid aluminum extensions up to 72″ in length. These are particularly handy when used with the Atto Back Blow Nozzle.
*Variable pull trigger – as the name implies, you can “vary the blast” by how hard (or not) you pull the trigger. Like I said before, you can do this – kind of – with a run of the mill commercial grade air gun, but it’s not very precise, and far from ergonomic. Here’s a short video showing just how sensitive that trigger pull is:
If you’d like to give one a try, EXAIR offers these – and any catalog product for that matter – with a 30 Day Unconditional Guarantee. We invite you to put it through its paces for up to a month. If it’s not going to work out for you, for any reason, we’ll arrange return for full credit. Give me a call – we can talk about how you intend to use it, and which one’s right for you.
EXAIR Optimization Products: Ultra Sonic Leak Detector Overview
Ultrasonic Leak DetectorThe Ultrasonic Leak Detector is a hand-held, high quality instrument that can locate costly leaks in a compressed air system. When using the Ultra Sonic Leak Detector, you only need to aim it in the direction of the suspected leak and if a leak is present an audible tone can be heard through the supplied headphones and the LED will light. This can be accomplished from up to 20′ away!
If you are not maintaining your compressed air system you can easily waste up to 30% of your compressor’s output through leaks. We all know compressed air is expensive, so mitigating wasteful leaks should be high on your to do list!
Since most compressed air leaks emit only Ultra Sonic sound it would be next to impossible to find a leak by listening for them since the sound is above the human thresh hold. That is where the EXAIR Ultrasonic Leak Detector comes in. Its sensitivity is is adjustable with 3 settings X1, X10 and X100 along with an on/off thumb wheel for fine sensitivity adjustments. The Ultra Sonic Leak Detector also comes with both a parabola or tubular extension to aim the unit and block out extraneous background noise.
If you have an application where you need to find an ultrasonic noise, you can speak with an Application Engineer to see if the model 9061 Ultrasonic Leak Detector could help.
If you would like to discuss the Ultra Sonic Leak Detector or any EXAIR product, I would enjoy hearing from you…give me a call.
Steve Harrison
Application Engineer
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Safety Air Guns – Using Engineered Air Nozzles For High Performance
Inexpensive air guns can be picked up just about anywhere, and you generally get what you pay for. Most will be very noisy and waste lots of compressed air. And many will be unsafe, violating two of OSHA’s standards put in place to protect worker safety. The first is Standard 29 CFR 1910.95(a) which sets limits to the maximum noise exposure, and the second is Standard 29 CFR 1910.242(b) which says that the nozzle cannot be dead-ended, or exceed a 30 PSIG pressure limit.
These guns may seem like a perfect fit for a handheld blowoff application. The truth is, the cost saved up front will easily be paid throughout the cost of ownership. This is due to the lack of an engineered nozzle which meets and exceeds the OSHA standards mentioned above. The “cheap” guns often have a cross drilled hole to meet or exceed the OSHA standard for dead-end pressure. While this may be true, it causes a large wind sheer which escalates noise levels to well over the allowable noise level exposure set by OSHA. These tips sometimes offer large force outputs because they are equivalent to an open pipe. We have publicized numerous times about how an open pipe blow off does not permit pressure to be utilized all the way to the point of blowoff, and is also a waste of energy.
In order to determine how much compressed air your current blow guns utilize, the level of noise they product, and the sound level they produce, consider taking advantage of the EXAIR Efficiency Lab. The Efficiency Lab is a free service that you can read more about here.
An EXAIR Safety Air Gun is engineered and designed to comply both of the OSHA standards mentioned above, ensuring safe operation for company personnel. On top of the safety designed into the guns, we also ensure all of our guns are efficient by offering only engineered nozzles on them.
EXAIR offers (4) types of Safety Air Guns – the VariBlast, the Soft Grip, the Heavy Duty, and the Super Blast. Each type of Safety Air Gun is offered with a plethora of nozzles, as well as varying length extensions, with or without the Chip Shield.
We invite you to try out an EXAIR Safety Air Gun, and get the free 1″ Wide Flat Super Air Nozzle as a bonus. Click here for more details about this special promotional offer.
To discuss your application and how an EXAIR Intelligent Compressed Air Product can improve your process, feel free to contact EXAIR, myself, or one of our other Application Engineers. We can help you determine the best solution!
Brian Bergmann
Application Engineer
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Twitter: @EXAIR_BB
EXAIR Super Air Amplifiers Compared to Fans
EXAIR Super Air Amplifiers and fans are designed to move air. Fans use motors and blades to push the air toward the target. There are two types, centrifugal fans and axial fans. Centrifugal fans are also called blowers or “squirrel” cages. The air enters into the side of the fan and is redirected 90 degrees to the outlet. The axial fans are box fans, ceiling fans, and industrial fans. The motor and spindle are attached to blades. The air enters from directly behind the fan, and the blades “slap” the air forward to the target. The EXAIR Super Air Amplifiers does not have any blades or motors to push the air. They use a Coanda profile with a patented shim to create a low pressure to draw in the air. (You can read more about it here: Intelligent Compressed Air: Utilization of the Coanda Effect.) I will expand a bit more in this blog about how each one performs in moving ambient air.
The reason to move air can vary by application from cooling, drying, cleaning, and conveying. The more air that can be moved, the better the performance for each of these functions. With the Super Air Amplifiers and fans, these products can move the air, but what affects air flow? Velocity, turbulence, and static or back pressure. As we look at each one, we can start to see the effectiveness within each application.
Velocity is air flow per unit area. This is the speed at which the air is traveling. Some fan designs can affect the velocity, like the motor and spindle in the center of the axial fan. Some of the area is removed from the middle of the flow region. So, the velocity is very weak in the center. (Reference diagram below). With the centrifugal fan, the air velocity has to be redirected and pushed out the exhaust. The velocity profile is very disoriented and will work against itself within the flow region. If we look at the EXAIR Super Air Amplifier, the center is open as shown above. There are no obstructions. Since we are drawing in the ambient air, the velocity profile is laminar meaning that the flow is even across the entire flow region. Laminar flow is optimum for a uniform force and effective blowing.
Turbulence is the “action” of the air flow. If the turbulence is high, the air flow pattern is interrupted and chaotic. It causes the velocity of the air to decrease quickly. By the time the air reaches the target, it has low energy and force. As a result of turbulence, noise levels can become very loud. With a centrifugal fan or blower, the air is forced to move at a right angle and pushed out through an exhaust port. This creates a very turbulent air flow. The axial fan has less turbulence than its counterpart, but the blades still “slap” the air to push it forward. This disruption in the flow pattern for both fans create turbulence and disarray. The EXAIR Super Air Amplifier draws the air into the device to generate very little turbulence on the exhaust end. The flow pattern is consistent, working together in the same direction. This will allow for more air to reach the target.
Static pressure is important as it relates to the amount of resistance or blockage. When blowing air through or around products, this resistance will determine the effectiveness and distance for efficient blowing. To find the maximum resistance, this would be considered at the dead-end pressure. When the exhaust is totally blocked, the maximum pressure is created. In an application, the higher the resistance, the less air that can flow through and around to be utilized. With fans, it is dependent on the blade types, motor size, and RPM. Since the EXAIR Super Air Amplifiers do not have motors or blades, it is determined by the inlet air pressure. So, the higher amount of static pressure, the more resistance that the blowing device can handle.
In comparison, I created a table below to show a model 120024 4” Super Air Amplifier against two different types of fans. The first thing that you notice is the small package area of the model 120024 as compared to the fans that create similar air flows. The centrifugal fan requires an addition electrical motor which increases the cost and generates a larger footprint. The reason for the smaller flow area is the laminar air flow that the Super Air Amplifiers generate. As stated above, the velocity pattern works together in the same direction. So, a smaller profile can produce a lot more air movement. In addition, this helps to create a larger static pressure. Also referenced above, it will move the air much further to do more work. With high turbulence, the air movement works against itself causing inefficiencies and louder noise levels.
In physics, it is much easier to pull than it is to push. The same goes for moving air. Fans are designed to “push” the air and the Super Air Amplifiers are designed to “pull” the air. This method of pulling makes it simple to create a laminar flow in a small package which is more efficient, effective, and quiet. Being powered by compressed air, there is no need for electric motors or blades to “push” the air ineffectively. With the patented shims inside the Super Air Amplifiers, they maximize the amplification by “pulling” in large amounts of ambient air while using less compressed air. If you want to move away from blower systems or axial fan systems to get better cooling, drying, cleaning, and conveying; you can contact an Application Engineer for more details.
John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb
Super Air Knife Cools Laminated Packaging Material
I recently worked with one of our distributors on a Super Air Knife application for a manufacturer of flexible packaging material. They create the plastic material that is commonly wrapped around the outside of a wide variety of different containers. The material exits the laminating machine at about 129°F (54°C) and must be cooled to close to room temperature before it is able to be rolled without the material sticking together.
They performed a test with a Model 110012, recording the temperature after the knife and determined that it would be suitable for them. Prior to using the Super Air Knife, they had been using a series of fans to cool down the material. This worked to some degree, but they had been experiencing quality issues as a result of inadequate levels of cooling and were forced to slow down the laminating machine in order to compensate. By implementing the Super Air Knife, they were able to cool the material down to ambient temperatures without having to slow production. As an added measure, they ordered a second knife to install on the underside to further decrease the temperature of the material.
The laminar airflow of the Super Air Knife is critical to the success of any cooling application. A fan “slaps” the air which provides random spikes of air at moderate velocities. The uniform, high velocity, laminar sheet of air from the Super Air Knife, in addition to the low compressed air consumption, makes it a much more effective cooling method than fans. The design of the Super Air Knife allows it to entrain ambient air at a rate of 40:1, maximizing the force and flow from the knife while keeping compressed air usage to a minimum.
Super Air Knives are available in a range of different materials and sizes. From stock EXAIR carries knives from 3”-108” in Aluminum, 303 Stainless Steel, 316 Stainless Steel, and 3”-54” in PVDF (Polyvinylidene Fluoride) for superior resistance to highly corrosive materials. In addition to being an excellent tool for cooling, the Super Air Knife can solve a wide range of drying and blowoff applications. If you have an application that would be better served with one of EXAIR’s Super Air Knives, reach out to us today and get yours on order! We ship same day from stock with orders received by 3:00 pm EST, stop wasting time with ineffective cooling or blowoff methods!
Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD
