What’s So Great About Air Entrainment?

Air entrainment is the phenomenon that occurs when air (or any gas) under pressure is released from a device in such a way that a low pressure is generated in the immediate area of the air (or gas) discharge.  Air (or gas) from the surrounding environment is then pulled (or entrained) into the discharged air stream, increasing its volumetric flow rate.  EXAIR Corporation has been engineering & manufacturing compressed air products to take maximum advantage of this phenomena since 1983…and we’ve gotten better & better at it over the past 36 years.

Obviously, the first thing that’s so great about air entrainment is…free air flow.  Every cubic foot that’s entrained means that’s a cubic foot that your compressor didn’t have to spend energy compressing.  Considering the EXAIR Super Air Knife’s entrainment ratio of 40:1, that makes for a VERY efficient use of your compressed air.

Another thing that’s so great about air entrainment is…it’s quiet.  As you can see from the graphic at the top of this blog, the Super Air Knife entrains air (the lighter, curved blue arrows) into the primary compressed air stream (the darker, straight blue arrows) from above and below.  The outer layers of the total developed flow are lower in velocity, and serve as a sound-attenuating boundary layer.  The sound level of a Super Air Knife (any length…here’s why) is only 69dBA.  That means if you’re talking with someone and a Super Air Knife is running right next to you, you can still use your “inside voice” and continue your conversation, unaffected by the sound of the air flow.

I always thought it would be helpful to have more than just a graphic with blue arrows to show the effect & magnitude of air entrainment.  A while back, I accidentally stumbled across a stunning visual depiction of just that, using a Super Air Knife.  I had the pleasure of talking with a caller about how effective a Super Air Knife might be in blowing light gauge paperboard pieces.  So I set one up in the EXAIR Demo Room, blowing straight upwards, and tossed paper plates into the air flow.  It worked just as expected, until one of the paper plates got a little closer to the Super Air Knife than I had planned:

As you can see, the tremendous amount of air flow being entrained…from both sides…was sufficient to pull in lightweight objects and ‘stick’ them to the surface that the entrained air was being drawn past.  While it doesn’t empirically prove the 40:1 ratio, it indisputably demonstrates that an awful lot of air is moving there.

If you’re looking for a quiet, efficient, and OSHA compliant solution for cleaning, blow off, drying, cooling…anything you need an even, consistent curtain of air flow for – look no further than the EXAIR Super Air Knife.  If you’d like to discuss a particular application and/or product selection, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Limiting Noise Exposure with Mufflers for Compressed Air

Mufflers come in many shapes and sizes. Each with their own benefits.

If you have ever walked into a manufacturing facility and heard the hiss or even worse the banshee scream of compressed air being exhausted to ambient, whether it be from a cylinder discharge, a timed drain going off, or a bypass valve being activated, they all could be hushed with a muffler. A muffler for compressed air comes in several shapes and sizes. EXAIR offers four separate types from stock to help attenuate the noise disruption within your facility.

The OSHA standard for allowable noise exposure is 29 CFR-1910.95(a) and outlines the number of hours per day any individual can be exposed to a particular noise level. These noise levels are expressed in decibels (dbA).

Hearing loss is the best known, but not the only, ill effect of harmful noise exposure. It can also cause physical and psychological stress, impair concentration, and contribute to workplace accidents or injuries.
Reclassifying Mufflers attenuating the exhaust of a pneumatic cylinder.

The first type I would like to showcase are the Reclassifying Mufflers. These are ideal for cylinder exhausts or valves which commonly contain an oil mist within the air stream which can easily contaminate the surrounding area. The patented design of the removable element separates oil from the exhausted air so virtually no atomized oil is released into the environment. They also attenuate the exhaust noise level up to 35 decibels. The filter element helps the exhaust to meet the OSHA Standard 29 CFR 1910.1000, a worker’s cumulative exposure to oil mist must not exceed 5 mg/m³ by volume in any eight hour shift of a forty hour work week.

The chart below helps to properly size the Reclassifying Muffler for a pneumatic cylinder. One key to proper installation of these mufflers is they must be installed vertically in order to properly trap and drain the oil.

Reclassifying Muffler Quick Pick Chart
Sintered Bronze mufflers are excellent choices for tight installation locations and are easily sized.

The next type of muffler to discuss are the Sintered Bronze Mufflers that are offered in ten different sizes. These are an excellent low cost solution which easily install into new or existing ports. Each size is designed to provide minimal back pressure and restriction for the individual port size. The quick pick chart below helps to easily select the correct size for attenuating the exhaust of a pneumatic cylinder. One key difference between these and the Reclassifying Mufflers is, these do not have to be oriented vertically as they do not collect the oil out of the exhaust air.

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The model 3913 – 3/4″ NPT Straight Through Muffler

If the process air needs to be directed or plumbed away from the operator then the Straight Through Mufflers are the ideal selection as they offer an NPT threaded inlet and exhaust. They are available in three standard NPT sizes from stock. These mufflers can be installed in any orientation and work well with our Vortex Tubes to help pass the cold air through while lowering the operating sound level of the tube. The average noise reduction of the Straight-Through Mufflers is 20 dB. This can easily reduce the noise level of an operation to below the OSHA standard requiring hearing protection for operators in the area.

The model 3903 Heavy Duty Muffler

The final option for mufflers from EXAIR are the Heavy Duty Mufflers. These are available in two sizes from stock and are constructed of corrosion-resistant aluminum with a stainless steel internal screen. These can be installed in any orientation and are ideal for protecting exhaust ports from contaminants that may clog or damage the device they are attached to. The typical noise reduction from installation is 14 dB with these mufflers.

These are available in two sizes from stock and are constructed of corrosion-resistant aluminum with a stainless steel internal screen. These can be installed in any orientation and are ideal for protecting exhaust ports from contaminants that may clog or damage the device they are attached to. The typical noise reduction from installation is 14 dB with these mufflers.

To summarize, EXAIR offers a multitude of options when it comes to lowering sound levels in operation areas that are caused by exhausted compressed air. Each of the mufflers discussed above are shipped same day from stock to meet your immediate need. If you are unsure of which muffler to use for your application, feel free to contact an Application Engineer.

Brian Farno
Application Engineer
Ph. 1-513-671-3322
BrianFarno@EXAIR.com
@EXAIR_BF

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

What is Sound and Interesting Facts About Sound

In physics, sound is a wave of pressure. It occurs in a medium, which can be a solid, liquid or gas. Sound cannot travel through a vacuum, such as in space. The wave of pressure reaches our ears and causes the ear drum to vibrate, which then goes through a complex process to ultimately be perceived as audible sound.

There are several characteristics of sound waves that can be measured and help define the sound. A sound wave can be visualized as a repeating sinusoidal wave (see below), and can be described by these properties – frequency and wavelength, amplitude, and speed.

Sound Wave
Sound Wave

  • Frequency is the number of cycles in 1 second, and is measured in Hertz (Hz)
  • Wavelength is the distance over which 1 cycle occurs, and for audible sound is  between 17 m and 17 mm long
  • Amplitude is the measure of its change over a single period, and normally a measure of sound loudness
  • Speed is the distance traveled per unit time

The speed of sound in air can be found using the equation:  a = Sqrt (γ•R•T)

where for air:
γ = ratio of specific heats = 1.4,
R = gas constant = 286 m²/s²/K
T = absolute temperature in °K (273.15 + °C)

At room temperature, 22°C (71.6°F), the speed of sound is 343.8 m/s (760 mph)

Some interesting facts about sound:

  • Sounds generally travels faster in solids and liquids than in gases.
  • You can estimate the distance from a lightning strike by counting the seconds that pass between seeing the lightning flash and hearing the thunder.  Take this duration an divide by 5 to get the distance away, in miles.
  • Humans normally hear sound frequencies between 20 Hz and 20,000 Hz.
  • Sound waves above 20,000 Hz are known as ultrasound, and sound waves below 20 Hz are known as infrasound.
  • Sound travel through water close to 4 times faster then through air.
  • The sound of a cracking whip occurs because the speed of the tip has exceeded the speed of sound.

Sound that is too loud can be a problem. The Occupational Safety and Health Administration (OSHA) has set limits on the noise exposure that an employee can be subjected. Exceeding these values can cause permanent damage to your ears and cause noise induced hearing loss. So, knowing and reducing the sound levels within a manufacturing operation is important.

OSHA Chart

EXAIR has many products that can help reduce the sound levels in your processes.  With products such Air Knives, Air Wipes, Air Amplifiers, Air Nozzles and Jets, and Safety Air Guns, strong, quiet and efficient blowoff, drying, and cooling can be performed.

Quiet Products

If you have questions about sound and keeping your sound levels in check or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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Video Blog: EXAIR’s Efficiency Lab

If you’d like to know how efficient (or not,) quiet (or not,) and effective (or not) your current compressed air devices are, the EXAIR Efficiency Lab can help.  For more details, we hope you’ll enjoy this short video.

If you’d like to talk about getting the most out of your compressed air system, we’d love to hear from you.

Russ Bowman
Application Engineer
EXAIR Corporation
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Sound – It Adds Up! How to Calculate Decibel Levels

Keeping noise levels in check and at safe levels is very important to ensure employee safety and well being.  OSHA (the Occupational Safety and Health Administration) through standard 29 CFR-1910.95(a) has studied the situation and set Maximum Allowable Noise Exposure limits in Hours per Day based on the Sound Level, in dBA, of exposure.

For existing processes, a Digital Sound Meter is a valuable tool to measure the sound level to ensure that the source of loud noises can be quickly identified and isolated for immediate corrective action.

For new processes, or changes to an existing process, it is important to estimate the sound level prior to installation and start-up, so that precautions can be taken as needed.

For example, let’s say we are going to add a blow off station to clean off a part on a conveyor to improve the process and increase the throughput.  A typical set-up might be a 12″ Super Air Knife (model 110012) blowing off the top and a pair of Super Air Nozzles (model 1100) to blow off the sides.

SAK and ASAN
12″ Super Air Knife and Super Air Nozzle

If we look at the performance data for the (2) different blow off devices, we find that the Super Air Knife is rated at 69 dBA and the nozzles at 74 dBA, when operated at 80 PSIG of compressed air supply.

SAK and ASAN

When asked, “what is the sound level for (1) of the knives, and (2) of the nozzles” a little Acoustic Engineering is in order. The decibel scale is logarithmic, and determining the total sound level when all (3) devices are in operation is not as easy as adding up the three sound level values (which would equal 218 dBA, way off the charts!).  Thankfully, both the actual sound level and the numerical value are determined another way.  I’ll spare you a lot of the math but the equation is as below.

Capture

… where SL1, SL2, SL3, … are the sound levels in dBA of the each sound makers, for as many that are being combined (in our example SL1 = 69, SL2 = 74 and SL3 = 74)

Plugging in the numbers into the equation, the combined sound level works out to be a quiet 77.65 dBA — well within the OSHA limit for exposure for a full 8 hour period.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can make your process better and quieter, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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EXAIR Products: Silencing Mufflers Overview

OSHA Standard 29 CFR 1910.95(a), relating to permissible noise exposure levels, states that when employees are subjected to sounds in excess of 90 dBA, some type of control should be used to reduce the sound level. In an industrial setting, it’s very common to find the exhausting air from air operated devices such as actuators, diaphragm pumps or cylinders for example, to produce sound levels well above the allowable limits set forth in the Standard. EXAIR offers a variety of different Silencing Mufflers that help to reduce this  noise level, while also increasing operator safety.

 

Reclassifying Mufflers are available in 1/8″, 1/4″, 3/8″, 1/2″, 3/4″ and 1″ NPT sizes

EXAIR’s Reclassifying Mufflers offer noise reduction up to 35 dB and are available in sizes ranging from 1/8″ to 1″ NPT. These types of mufflers are often considered”dual-purpose” as they not only reduce the noise level but also remove oil from the exhaust airflow by incorporating a removable filter element.  The exhausting oil mist is reduced from 50 PPM (parts per million) to only 0.015 PPM, when the device is operated at 100 PSIG. In addition, there is a bowl on the bottom to capture any residual oil and a 1/4″ tube adaptor to allow for easy draining.

Sintered Bronze Mufflers are available in #10-32, 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, 1″, 1-1/4″ and 1-1/2″ NPT sizes, as well as 1/2-20 UNF female for use with solenoid valves

Straight Through Mufflers are available in 1/4″, 3/8″ and 3/4″ MNPT x FNPT

Sintered Bronze Mufflers are a relatively low cost option, commonly used with air cylinders as they can be installed quick and easy. We offer 1o different sizes, ranging from #10-32 for small installations, up to 1-1/2″ NPT for larger scale applications. The noise reduction depends on the size of the muffler and back pressure, which can occur from dirt or particulate clogging the muffler, restricting the exhausting airflow from passing through the porous sintered bronze.

Our Straight Through Mufflers are made of corrosion resistant aluminum and are lined with a sound absorbing foam, capable of reducing noise levels up to 20 dB. We offer 3 different sizes, 1/4″, 3/8″ and 3/4″ NPT, with a male thread on one end and female thread on the other. We incorporate this muffler design into our Cold Guns and Adjustable Spot Coolers and they are commonly used with our Vortex Tubes, Cabinet Cooler® Systems and E-Vac® Vacuum Generators as well.

Heavy Duty Mufflers are available in 1/4″ and 3/8″ FNPT

Lastly, the Heavy Duty Mufflers feature an internal, 50 mesh stainless steel screen, to protect against contaminants in the airflow,  and a corrosion resistant aluminum outer shell. In most cases, the sound reduction can be as high as 14 dB and we offer 2 different sizes, 1/4″ and 3/8″ FNPT. These types of mufflers are regularly used on the hot air exhaust of our Vortex Tubes.

For help with product selection or to discuss a particular process, please contact one of our application engineers at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

Calibration – Keep Your Meters True

EXAIR offers meters to measure the level of physical parameters such as sound and static. Each meter has sensitive electrical circuitry and a periodic calibration is recommended to ensure the meter readings are tried and true.

The model 9104 Digital Sound Level Meter is an easy to use instrument that measures and monitors the sound level pressure in a wide variety of industrial environments. The source of loud noises can be quickly identified so that corrective measures can be taken to keep sound levels at or below OSHA maximum allowable exposure limits.

The sound meter comes from the factory with an NIST (National Institute of Standards and Technology) certificate of accuracy and calibration.  As a good practice, EXAIR recommends a yearly calibration of the instrument, and we offer a service that calibrates the unit to the same NIST standards and provide a written report of the calibration.

The model 7905 Static Meter allows easy one-hand static measurements.  It is useful in both locating sources of high static charge and checking the reduction of static after treatment with an EXAIR Static Elimination product.  The unit is sensitive and responsive, and indicates the the surface polarity of objects up to +/- 20 kV when measured from 1″ away.

It is also recommended that the Static Meter be calibrated on a yearly basis.  EXAIR offers (3) levels of calibration service.  The first two provide calibration in accordance with MIL Standards using accepted procedures and standards traceable to NIST.  The third calibration service conforms to the same Mil Standard, as well as ISO/IEC standards.

Annual calibration service of your EXAIR Digital Sound and Static Meter, along with proper care and storage, will keep your meter performing tried and true for many years, providing accurate and useful measurements.

To initiate a calibration service, give us a call and an Application Engineer will issue an Returned Good number, and provide instructions on how to ship the meter to EXAIR.

If you have questions regarding calibration services for your meters 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

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