Understanding Decibels & Why OSHA Pays Attention to Your Noise Exposure

In the simplest of metric terms, a decibel is one-tenth of a bel.  But, historically, bel was a unit created to honor Alexander Graham Bell who invented the telephone.  In the early days with telephone wires, they noticed that the signal strength would decay over a long distance.  In order to determine power requirements to connect people for communications, they determined that they could use the ratio of power levels.  As a start, it had to be based on a minimum amount of power required for a person to hear on the telephone.  They found that the signal power level to generate an angular frequency of 5000 radians per second would be that minimum value as determined by an average number of people.  They used this mark as a reference point in the ratio of power levels.  Because of the large variations in values, they simplified the equation on a base-10 log scale and dividing the bel unit by 10.  Thus, creating the measurement of decibel.

Today, this same method is used to measure sound.  Like frequency waves that travel through the telephone wires, pressure waves travel through the air as sound.  This sound pressure is what our ears can detect as loudness, and it has a pressure unit of Pascals (Pa).  As an example, a small sound pressure would be like a whisper while a large sound pressure would be like a jet engine.  This is very important to know as high sound pressures, or loudness, can permanently damage our ears.

With sound pressures, we can determine the Sound Pressure Level (SPL) which is measured in decibels (dB).  Similar to the equation for the telephone power signals above, the SPL also uses a ratio of sound pressures in a base-10 logarithmic scale.  For a minimum reference point, an average human can just start to hear a sound pressure at 0.00002 Pa.  So, the equation for measuring sound levels will use this minimum reference point as shown in Equation 1.

Equation 1:

L = 20 * Log10 (p/pref)

where:

L – Sound Pressure Level, dB

p – Sound pressure, Pa

pref – reference sound pressure, 0.00002 Pa

Why is this important to know the decibels?  OSHA created a chart in 29CFR-1910.95(a) that shows the different noise levels with exposure times.  This chart was created to protect the operators from hearing loss in work environments.  If the noise level exceeds the limit, then the operators will have to wear Personal Protection Equipment (PPE), or suffer hearing damage.  EXAIR offers a Sound Level Meter, model 9104, to measure sound levels in decibels.  It comes calibrated to accurately measure the sound to determine if you have a safe work environment.

Sound Level Meter

There is a term that is used when it comes to loud noises, NIHL.  This stands for Noise Induced Hearing Loss.  Once hearing is damaged, it will not come back.  To keep your operators safe and reduce NIHL, EXAIR offers many different types of blow-off products that are designed to decrease noise to a safe level.  So, here’s to Alexander Graham Bell for creating the telephone which can be used to contact EXAIR if you have any questions.

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

 

Photo of Telephone by Alexas_FotosCC0 Create Commons

General Good Ideas For The Compressor Room

When considering your compressor room all too often the phrase applies “out of sight and out of mind”.  Of course, we all know that is not a good approach to the compressor room or really anything in life.  Unfortunately, many of us take for granted that very system that delivers the power to keep our machines, equipment and tools operating.

Air Compressor
Compressor Room Located Outdoors

So, what can we do keep the ‘lungs” of our plants performing reliably and efficiently?  Since this Blog is about “General Good Ideas For The Compressor Room”, I have some points below for your consideration.

  • Ideally the compressor room should be centrally located to minimize the length of the pipes and allows for easier noise control. With long piping runs leaks become more likely and frictional losses are increased.
  • The compressor room should be sized to allow for easy maintenance and future expansion.
  • For efficient operation air compressors need clean intake air. Intake air that is dusty, dirty or contains gaseous contamination will reduce the efficiency and possibly the longevity of your equipment.
  • The compressor room needs adequate ventilation since air compressors generate significant heat. If excessive heat is allowed to build up it reduces the efficiency of the air compressor raising utility costs, causes compressor lubricant to break down prematurely that could possibly result in increased maintenance and compressor failure.
  • What is the velocity of the air through the main headers? If the speed is above 1200 FPM many dryers have reduced efficiency and speeds greater than this can also carry moisture past the drainage drop legs.
  • Excess friction caused by too small of a diameter piping creates pressure loss, which reduces efficiency and if the compressor is ran above its pressure rating to overcome the frictional losses increases energy consumption, maintenance costs and down time.

Now that your compressor room is shipshape in Bristol fashion, you might think that all is well.  While that may be true, chances are there are other significant additional savings to be had.  EXAIR specializes in point of use compressed air products that are highly efficient and quiet!  If you have any blow-offs that are open tube or howl as loud as the ghost of Christmas yet to come, check out EXAIR’s Super Air Nozzles.  They are highly efficient and quiet, in fact they meet OSHA Standard 29 CFR – 1941.95 for maximum allowable noise and OSHA Standard 29 CFR 1910.242 (b) for higher than 30 PSIG blow-off pressure.  All of EXAIR’s compressed air products are engineered to minimize compressed air consumption and take advantage of the Coanda effect.  Simply stated EXAIR’s highly engineered, intelligent designs entrain (combine) ambient air with the compressed air supply which saves you money!

nozzle_anim_twit800x320
EXAIR Super Air Nozzle entrainment

EXAIR also offers the Ultra Sonic Leak Detector.  Simply point the device at a suspected leak which are typically found at unions, pipes, valves and fittings from up to 20’ away.   Plants that are not maintaining their plumbing can waste up to 30% of their compressors output through undetected leaks.

ultrasonic_2
EXAIR Ultra Sonic Leak Detector

EXAIR has a complete optimization product line that the Ultra Sonic Leak Detector is in that includes the Electronic Flow Control, Digital Flowmeter’s and a Digital Sound Level Meter.  All designed to either increase the safety or efficiency of your compressed air usage.

EXAIR has 15 other product lines all designed to increase your process efficiency and save you money by using you compressed air supply efficiently.  Why not visit the EXAIR website or call and request a free catalog?

When you are looking for expert advice on safe, quiet and efficient point of use compressed air products give us a call.   We would enjoy hearing from you!

Steve Harrison
Application Engineer
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Image taken from the Best Practices for Compressed Air Systems Handbook, 2nd Edition

Ultrasonic Leak Detector: Because Leaks Won’t Find (Or Fix) Themselves

I once worked in an equipment repair shop with a small and simple compressed air system…just a 5HP single acting piston compressor that sat atop a 50 gallon tank, in the corner by “The Big Truck”. The majority of our work was field service, and management was big on maintaining our service trucks, so we checked tire pressures every Monday morning as we rolled out, and kept a tire chuck handy to ensure proper inflation. It was also used to supply a couple of air guns that were used at our drill press and soldering/assembly station. One morning, I noticed the air compressor was running when I arrived…I thought it was odd, because I knew for a fact it hadn’t been used in at least 16 hours, but that compressed air went someplace, right? We had a leak. Well, at least one.

This was mid-December, and the week between Christmas and New Year’s Day was characteristically slow, and typically devoted to a thorough shop cleaning. We also took the opportunity to get some bottles of soapy water and check for leaks at the handful of pipe fittings that comprised the system…for the uninitiated, if you have a leaky fitting, the escaping air blows bubbles in the soapy water (a cheap, messy way in other words). We found some bubbling, undid those fittings, cleaned them, and applied fresh pipe thread sealant (I don’t want to start any arguments, but I was taught that tape is more of a thread protectant than an effective sealing agent) and, in addition to replacing a couple of well-worn hoses, we were up and running.  And we never heard the compressor running first thing in the morning again.

Not all compressed air systems are as simple as that, though.  Many go from a room with several large & sophisticated air compressors, to corners of every building on the grounds.  Through valves & manifolds, to cylinders, machinery and blow offs, with more connections than you could soap-and-water check in a month.

In those cases, the EXAIR Model 9061 Ultrasonic Leak Detector makes short(er) work of finding the leaks.  With both visual (LED’s on the face) and audible (headphones) indications, even very small leaks are easy to detect with the parabola installed.  The precise location can then be found with the tubular extension.

EXAIR Ultrasonic Leak Detector “hones in” on the exact location of a leak in a compressed air line.

You’ll still have to fix the leaks yourself, but finding them is oftentimes more than half the battle.  And, once fixed, it can be worth a million (cubic feet of compressed air, that is.)

EXAIR’s Ultrasonic Leak Detectors are not only useful for finding compressed air leaks; they’re popular in a variety of other areas:

Additionally, they can be used to identify faulty bearings, brake systems, tire & tube leaks, engine seals, radiators, electrical relay arcing…anything that generates an ultrasonic sound wave.  If you’d like to find out more, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Sound Power Vs Sound Pressure

sound-level-comparison
EXAIR Intelligent Compressed Air Product dBA ratings as compared to other sounds

When trying to explain or state a number associated with how loud a sound or noise is it can be somewhat confusing or at the very least, ambiguous.  This blog will help to make it clear and easy to understand the difference between Sound Power and Sound Pressure.

Sound Power is defined as the speed at which sound energy is radiated or transmitted for a given period of time.  The SI unit of sound power is the watt. It is the power of the sound force on a surface of the medium of propagation of the sound wave.

Sound Pressure is the sound we hear and is defined as the atmospheric pressure disturbance that can vary by the conditions that the sound waves encounter such as furnishings in a room or if outdoors trees, buildings, etc.  The unit of measurement for Sound Pressure is the decibel and its abbreviation is the dB.

I know, the difference is still clear as mud!  Lets consider a simple analogy using a light bulb.  A light bulb uses electricity to make light so the power required (stated in Watts) to light the bulb would be the “Sound Power” and the light generated or more specific the brightness is the “Sound Pressure”.  Sound just as with the light emitting from the bulb diminishes as the distance increases from the source.  Skipping the math to do this, it works out that the sound decreases by 6 dB as the distance from the sound source is doubled.  A decrease of 3dB is half as loud (Sound Pressure) as the original source.  As an example sound measured at 90 dB @ 36″ from the source would be 87dB at 54″ from the sound source or 84dB at 72″.

We at EXAIR specialize in making quiet and efficient point of use compressed air products, in fact most of our products either meet or exceed OSHA noise standards seen below.

OSHA Noise Level

EXAIR also offers the model 9104 Digital Sound Level Meter.  It is an easy to use instrument for measuring and monitoring the sound level pressures in and around equipment and other manufacturing processes.

If you have questions about the Digital Sound Level Meter, or would like to talk about any of the quiet EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR or any Application Engineer.

Steve Harrison
Application Engineer

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Cleaning Glass After a Cutting Machine, Super Air Knives to the Rescue

Glass cutting machine

A glass cutting facility was having issues with small shards of glass leaving the cutting machine.  After scribing and breaking individual panes, small pieces of glass would come apart from the edges of the glass.  These glass fragments would go downstream causing cuts on transport wheels as well as creating blemishes in the surface of the glass.  They needed a non-contact way to clean the glass as the panes left the cutting machine.

Their operation started with a 156” (3.96m) wide sheet of glass placed at the front of the cutting machine.  The glass was moved into the machine where it would scribe different dimensions and sizes to minimize any scrap.  As the machine was scribing, a protective separator would close off the cutting machine to protect the operators.  Once finished, the protective separator would open, allowing the glass sheet to exit on the other side of the machine.  As the glass was coming out, a break device would “crack” the glass panes on the scribed lines.  They wanted to clean the surface as the glass sheet was coming out to keep the fragments in the machine.

EXAIR Super Air Knife model 1100108

EXAIR has always been the leader in manufacturing the longest air knives in the industry.  The EXAIR Super Air Knives can be manufactured up to 108” (2.74m) long in one continuous length.  But, for this application, we had to tackle it in a different manner to reach across the entire width of 156” (3.96m).  EXAIR had a solution, the model 110900 Coupling Bracket Kit.  This can combine aluminum Super Air Knives for additional length.  It has all the hardware to securely attach the Super Air Knives end-to-end to get a continuous air flow along the entire length.  With the Coupling Bracket Kit, I recommended a model 110072, 72” (1.83m) long aluminum Super Air Knife with a model 110084, 84” (2.13m) aluminum Super Air Knife.  The customer was now able to clean the entire section of glass just in front of the exit of the cutting machine.  With the air knives directed to blow at a slight angle in the counter-flow direction, this non-contact form of cleaning was able to keep the shards inside the machine without scratching the surfaces.

Air Knife Coupling Bracket Kit

The Super Air Knives are designed to be the most efficient air knives in the market place.  It has a 40:1 amplification ratio which entrains 40 parts of ambient air to every 1 part of compressed air.  So, it will save you compressed air which in turn, will save you money.  Here at EXAIR, we like to go one step further for our customers.  EXAIR offers an Optimization product line to save the customer even more money, to reduce even more waste, and to become even more energy efficient.  For this customer above, I recommended an Electronic Flow Control, EFC.  This uses a photoelectric sensor to turn on a system only when compressed air is needed.  It is a small PLC unit with a timer control.  I recommended the model 9064-2 which has two solenoid valves to operate each Super Air Knife.  The photoelectric sensor can be adjusted for light and dark object, but for glass, we had to look for an alternative way.  I was able to have the customer place it on the protective separator.  Now, the Super Air Knives will remain turned off until after the scribing was completed. When the separator moved up, it would trigger the timing operation of the EFC.  By adding the EFC to their system, they were able to reduce the amount of compressed air by one-half.

click on picture for mor information

If you have a wide area that needs to be blown off, cooled, or dried; EXAIR may have a solution for you.  For the customer above, EXAIR was able to combine Super Air Knives with optimization for an efficient and effective way to clean a wide surface.  If you would like to discuss a solution for your “wide” application, you can contact an Application Engineer at EXAIR to discuss.

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

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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An Ultrasonic Leak Detector Helps with a Pressure Decay Leak Detector

Ultrasonic Leak Detector

A manufacturing company had a pressure decay leak system to check for leaks in compressed air housings.  Their detector was able to find leaks as small as 0.02 cc/min.  The leak program was designed for recording each housing with a batch/lot number and the corresponding leak data.  If the housing reached or surpassed the leak limit, the part would be marked and quarantined.  The pressure decay leak detector was a sensitive instrument, but it could not tell the operator where the leak was occurring.

How the pressure decay leak detector worked was by pressurizing the housing to a target pressure.  The flow valves would shut, isolating the housing.  After the pressure stabilized, the sensitive pressure sensors would pick up any loss in pressure over time.  If the leak limit wasn’t reached, a green light would indicate a good leak test.  If the limit was reached, a red light would indicate a failed leak test, and the housing would have to be segregated.

Reference Filter Housing

The housing design used a head, a bowl, a drain, and a differential pressure gauge.  The leak paths were numerous.  It could be at the drain, between the drain and the bowl, between the head and bowl, at the differential pressure gauge, and even in the casting of the head.  The heads were made from a die-casted aluminum.  If the process was not done properly, porosity could occur in the head.  The leak detector was sensitive enough to find any voids that would allow air to pass through the head casting.  With these many areas of potential leaks, it could be problematic if the reject rate was high.

For the application above, it is important to find where the leaks are occurring in order to create a corrective action.  In order to find the leaks, they purchased a model 9061 Ultrasonic Leak Detector from EXAIR.  Instead of pressure decay, the Ultrasonic Leak Detector uses sound.  Whenever a leak occurs, it will generate an ultrasonic noise.  These noises have a range of frequencies from audible to inaudible.  The frequencies in the range of 20 Khz to 100 Khz are above human hearing, and the Ultrasonic Leak Detector can pick up these high frequencies, making the inaudible leaks, audible.  The model 9061 has three sensitivity ranges and a LED display; so, you can find very small leaks.  This unit comes with two attachments.  The parabola attachment can locate leaks up to 20 feet (6.1 meters) away.  And the tube attachment can define the exact location.  With this application, they used the tube attachment to locate the leaks.  After retesting the failed housings, they found that 80% of the rejects were from a sealing surface.  They were able to replace or repair the o-rings.  10% of the leaks were coming from the drain.  3% of the rejects were leaking at the differential pressure gage.  Both the drains and the pressure gages could be replaced with new units.  7% of the housings had a porosity problem in the head of the housing.  For these, they were shipped back for evaluation to create a modification for a better casting.  The production manager shared with me that an extra vent hole was required to reduce the void.  This was a huge savings for the die-caster and manufacturing plant.

EXAIR Ultrasonic Leak Detector is a great tool.  It can be used in a variety of applications including compressed air systems, bearing wear, circuit breakers, refrigerant leaks, and gas burners to name few.  For the company above, it was a great tool to improve their assembly and testing process for their housings.  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.

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