Sound Power Level and Sound Pressure

Energy…all day (and night) long, we humans are surrounded by – and bombarded by – all kinds of energy. Sometimes, the effects are pleasant; even beneficial: the warmth of the sun’s rays (solar energy) on a nice spring day is the sure-fire cure for Seasonal Affective Disorder, and is also the catalyst your body needs to produce vitamin D. Good things, both. And great reasons to get outside a little more often.

Sometimes, the effects aren’t so pleasant, and they can even be harmful. Lengthy, unprotected exposure to that same wonderful sun’s rays will give you a nasty sunburn. Which can lead to skin cancer. Not good things, either. And great reasons to regularly apply sunblock, and/or limit exposure if you can.

Sound is another constant source of energy that we’re exposed to, and one we can’t simply escape by going inside. Especially if “inside” is a factory, machine shop, or a concert arena. This brings me to the first point of today’s blog: sound power.

Strictly speaking, power is energy per unit time, and can be applied to energy generation (like how much HP an engine generates as it runs) or energy consumption (like how much HP a motor uses as it turns its shaft) For discussions of sound, though, sound power level is applied to the generation end. This is what we mean when we talk about how much sound is made by a punch press, a machine tool, or a rock band’s sound system.

Sound pressure, in contrast, is a measure of the sound power’s intensity at the target’s (e.g., your ear’s) distance from the source. The farther away you get from the sound’s generation, the lower the sound pressure will be. But the sound power didn’t change.

Just like the power made by an engine and used by a motor are both defined in the same units – usually horsepower or watts – sound power level (e.g. generation) and sound pressure (e.g. “use” by your ears) use the same unit of measure: the decibel.  The big difference, though, is that while power levels of machinery in motion are linear in scale, sound power level and pressure scales are logarithmic.  And that’s where the math can get kind of challenging.  But if you’re up for it, let’s look at how you calculate sound power level:

Sound Power Level Equation


Wis reference power (in Watts,) normally considered to be 10-12 W, which is the lowest sound perceptible to the human ear under ideal conditions, and

W is the published sound power of the device (in Watts.)

That’s going to give you the sound power level, in decibels, being generated by the sound source.  To calculate the sound pressure level:

Sound Power Level to Sound Pressure Equation


Lis the sound power level…see above, and

A is the surface area at a given distance.  If the sound is emitted equally in all directions, we can use the formula for hemispheric area, 2πrwhere r=distance from source to calculate the area.

These formulas ignore any effects from the acoustic qualities of the space in which the sound is occurring.  Many factors will affect this, such as how much sound energy the walls and ceiling will absorb or reflect.  This is determined by the material(s) of construction, the height of the ceiling, etc.

These formulas may help you get a “big picture” idea of the sound levels you might expect in applications where the input data is available.  Aside from that, they certainly put into perspective the importance of hearing protection when an analysis reveals higher levels.  OSHA puts the following limits on personnel exposure to certain noise levels:

Working in areas that exceed these levels will require hearing protection.

EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind.  If you’d like to talk about how we can help protect you and your folks’ hearing, call us.


EXAIR’s Unconditional 30 Day Guarantee = Success!

This week in Cincinnati we hit a record high 79°F. Since less than a week earlier it snowed all afternoon, let’s just say many people around here began to get excited. While I don’t mind a little snow here and there, once February begins to draw to a close I’m ready to bust out the shorts, tank tops and flip flops and bring on some warmer temperatures. It also means I’m right around the corner from opening up the pool. Let’s hope that goes much smoother than last year….


Another benefit to the warmer temperatures, especially here in Cincinnati, is the coming of the baseball season. With the Reds Spring Training also starting this week, optimism is in the air (albeit reserved after the last few years performance).

Unlike baseball where it’s 3 strikes and youuuu’rrrreeee out! EXAIR’s unconditional 30 day guarantee for all stock products allows you the opportunity to test out several different solutions to ensure you get the right product for your application.30dayguarantee

I recently worked with a customer that was interested in switching their current blowoff process with something that would reduce their sound levels but still allow them to complete the job in a similar time frame. The company makes aluminum castings and was using the air gun to remove residual sand leftover in the die after each cycle. Their current air gun was producing sound levels at 107 dBA, well above OSHA’s safe operating range for a full 8 hour shift of work according to OSHA 29 CFR 1910.95(a).

They didn’t want to commit to just one style of air gun, so he purchased a 1210SS-18 (Safety Air Gun w/ ¼ NPT Stainless Steel Nozzle and 18” extension) and a few different additional ¼ NPT nozzles to see which style his operators preferred. After some testing, they concluded that the air gun with an 1122SS 2” Flat Nozzle installed provided them with the best results. Having the added feature of changing out the shim to increase/decrease the force and flow was also welcomed. They’ll be returning the extra nozzles and applying the credit to the purchase of some new 1230SS-18 guns to outfit their other work stations.

Model 1230SS-18 Soft Grip Safety Air Gun

While we do have a highly trained team of Application Engineers ready and available to help you determine the most suitable product, sometimes testing it out at your facility is the best way to ensure a positive result. That is EXACTLY why we give you 30 days to test out any stock product. If for any reason at all you’re unsatisfied with the performance, give us a call and we’ll arrange for a return. Don’t be afraid to swing and miss!

Tyler Daniel
Application Engineer
Twitter: @EXAIR_TD

Reds photo courtesy of Keith via Creative Commons License

Oil Removal Filters – Keeping Compressed Air Clean

Compressed air filters help to keep the air clean and condensate free to protect equipment from dust, dirt, pipe scale, oil and water. Even though the compressed air system will typically have a main dryer, additional treatment is often necessary. For this discussion, we will focus on the oil removal process and filter type.

After the compressed air has passed through a particulate filter, the dirt, dust and water droplets have been removed.  Oil that is present is much smaller in size, and mostly passes though the particulate filter.  The installation of a coalescing filter will provide for the removal of the majority of the fine oil aerosols that remain. The coalescing filter works differently than the particulate filters. The compressed air flows from inside to outside through the coalescing filter media. The term ‘coalesce’ means to ‘come together’ or ‘form one mass.’  The process of coalescing filtration is a continuous process where the small aerosols of oil come in contact with fibers of the filter media. As other aerosols are collected, they will join up and ‘come together’ and grow to become an oil droplet, on the downstream or outside surface of the media.  Gravity will then cause the droplet to drain away and fall off the filter element.

Example of a 0.03 Micron Coalescing Oil Removal Filter

Some important information to keep in mind –

  • Change the filter regularly, not just when the differential pressures exceeds recommended limits, typically 5 PSI
  • Coalescing filters will remove solids too, at a higher capture rate due to the fine level of filtration, using a pre-filter for solids will extend the life
  • Oil free compressors do not provide oil free air, as the atmospheric air drawn in for compression contains oil vapors that will cool and condense in the compressed air system.

If you would like to talk about oil removal filters or any of the EXAIR Intelligent Compressed Air® Products, 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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Twitter: @EXAIR_BB

Designing a Compressed Air Distribution System

Compressed air is used to operate pneumatic systems in a facility, and it can be segregated into three sections; the supply side, the demand side, and the distribution system.  The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air.  They are generally located in a compressor room somewhere in the corner of the plant.  The demand side are the collection of end-use devices that will use the compressed air to do “work”.  These pneumatic components are generally scattered throughout the facility.  To connect the supply side to the demand side, a compressed air distribution system is required.  Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices.  For a sound compressed air system, the three sections have to work together to make an effective and efficient system.

An analogy, I like to compare to the compressed air system, is an electrical system.  The air compressor will be considered the voltage source, and the pneumatic devices will be marked as light bulbs.  To connect the light bulbs to the voltage source, electrical wires are needed.  The distribution system will represent the electrical wires.  If the wire gauge is too small to supply the light bulbs, the wire will heat up and the voltage will drop.  This heat is given off as wasted energy, and the light bulbs will dim.

The same thing happens within a compressed air system.  If the piping size is too small, a pressure drop will occur.  This is also wasted energy.   In both types of systems, wasted energy is wasted money.  One of the largest systematic problems with compressed air systems is pressure drop.  If too large of a pressure loss occurs, the pneumatic equipment will not have enough power to operate effectively.  As shown in the illustration below, you can see how the pressure decreases from the supply side to the demand side.  With a properly designed distribution system, energy can be saved, and in reference to my analogy, it will keep the lights on.

Source: Compressed Air Challenge Organization

To optimize the compressed air system, we need to reduce the amount of wasted energy; pressure drop.   Pressure drop is based on restrictions, obstructions, and piping surface.  If we evaluate each one, a properly designed distribution system can limit the unnecessary problems that can rob the “power” from your pneumatic equipment.

  1. Restriction: This is the most common type of pressure drop. The air flow is forced into small areas, causing high velocities.  The high velocity creates turbulent flow which increases the losses in air pressure.  Flow within the pipe is directly related to the velocity times the square of the diameter.  So, if you cut the I.D. of the pipe by one-half, the flow rating will be reduced to 25% of the original rating; or the velocity will increase by four times.  Restriction can come in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters and regulators.
  2. Obstruction: This is generally caused by the type of fittings that are used.  To help reduce additional pressure drops use sweeping elbows and 45-degree fittings instead of 90 deg. elbows.  Another option is to use full flow ball valves and butterfly valves instead of seated valves and needle valves.  If a blocking valve or cap is used for future expansion, try and extend the pipe an additional 10 times the diameter of the pipe to help remove any turbulence caused from air flow disruptions.  Removing sharp turns and abrupt stops will keep the velocity in a more laminar state.
  3. Roughness: With long runs of pipe, the piping surface can affect the compressed air stream. As an example, carbon steel piping has a relative rough texture.  But, over time, the surface will start to rust creating even a rougher surface.  This roughness will restrain the flow, creating the pressure to drop.  Aluminum and stainless steel tubing have much smoother surfaces and are not as susceptible to pressure drops caused by roughness or corrosion.

As a rule, air velocities will determine the correct pipe size.  It is beneficial to oversize the pipe to accommodate for any expansions in the future.  For header pipes, the velocities should not be more than 20 feet/min (6 meter/min).  For the distribution lines, the velocities should not exceed 30 feet/min (9 meter/min).  In following these simple rules, the distribution system can effectively supply the necessary compressed air from the supply side to the demand side.

To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use.  By following the tips above, you can reach that goal and have the supply side, demand side, and distribution system working at peak efficiency.  If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side.  This would be the pneumatic equivalent of changing those light bulbs at the point-of-use into LEDs.

John Ball
Application Engineer
Twitter: @EXAIR_jb


Photo: Light Bulb by qimonoCreative Commons CC0


Intelligent Compressed Air: Bernoulli’s Principle


Daniel Bernoulli was a Swiss mathematician and physicist born in 1700. He is most known for the Bernoulli principle, published in his book Hydrodynamica in 1739. The Bernoulli’s principle states that an increase in speed of a fluid will result in a decrease in pressure. As a fluid moves from a wider pipe to a narrow one, the fluid begins to move faster. The given volume of the fluid moving from one point to another over a set amount of time will not change. In order for the same amount of fluid to pass through a smaller orifice, it must speed up. This is displayed quite well in the flow of a river. At wide, open spaces the river flows slowly. In areas that become narrow, for example by a canyon wall, the speed of the river’s flow increases dramatically.

The Bernoulli principle also provides an explanation for the lift that is created on an airplane wing. When air encounters an obstacle (in this case an airplane wing), its path will narrow as it flows around the object. As this stream of air speeds up, some of the energy from the random motion of the air molecules must be converted into energy of the stream’s forward flow. Pressure is created by the random motion of these air molecules. Transferring this energy into the stream flow then results in a drop in the air pressure. An airplane wing is shaped so that the air must move faster over it than under it. This causes the slower moving air underneath to exert more pressure on the wing than the air moving across the top. This is referred to as lift and is what allows an airplane to fly.

Temperatures are beginning to creep back up here in Cincinnati and just last week pitchers and catchers for the Cincinnati Reds reported for Spring Training. They’ll also be watching Bernoulli’s principle in action. The oft-dreaded (for batters, anyway) 12-6 curveball occurs due to the way the pitcher forces the ball to spin. Due to way he grips the ball across the laces and imparts this spinning motion, more air pressure forms on the top of the ball. This causes the bottom of the ball to accelerate downwards, resulting in the phenomenon that drives many baseball players crazy as they swing and miss due to a miscalculation of the ball’s position.


Some of EXAIR’s products also utilize the Bernoulli Principle. As the high-velocity air exits the nozzle of a Super Air Knife, a low pressure area is created that draws in surrounding ambient air at a rate of 40:1. The same also occurs with the Super Air Amplifiers, Adjustable Air Amplifiers, and Air Nozzles. If you’d like to discuss the application of any of our Intelligent Compressed Air Products, give an Application Engineer a call today.

Tyler Daniel
Application Engineer
Twitter: @EXAIR_TD


River image courtesy of Sasori33 via Creative Commons License
Reds image courtesy of Lisa via Creative Commons License

Need to Cool Tooling but Limited On Compressed Air? Consider the Mini Cooler

I recently had a chat conversation with a customer who was looking to cool the tooling on his CNC router, mill and lathe in his small machine shop. During the machining process, as the tooling would begin to heat up, it would warp the bit, causing irregularities in the finished product. In some cases the tooling was getting so hot, it would actually break, creating a safety concern.

He had reviewed some of our cooling products and was thinking of using our Cold Gun in the application but was concerned with the air demand. The Cold Gun consumes 15 SCFM @ 100 PSIG and provides a 50°F temperature drop (from supply temperature) with 1,000 Btu/hr. of cooling capacity. The problem was that his compressor only produces a little over 9 SCFM. I explained that the existing compressor would in fact be undersized as it doesn’t produce enough volume to keep up with the demand of the Cold Gun.

Model 3808 Mini Cooler System with Single Point Hose Kit, includes swivel magnetic base and filter separator to remove moisture and particulate from the air supply.

Due to the limited amount of compressed air available, our Mini Cooler System, Model # 3808, would be the better solution. The Mini Cooler also provides a 50°F temperature drop with a little less cooling power, 550 Btu/hr., but this system only requires 8 SCFM @ 100 PSIG, falling within the existing compressor’s output capacity. The Mini Cooler also includes a magnetic base as well as flexible tubing to direct the cold air to the desired location, making it easy to move from machine to machine.

The Mini Cooler is the ideal solution for small tool or part cooling, with minimal air consumption.

If you are considering an EXAIR product for an application or have additional questions about performance, contact an application engineer for assistance in making the best selection.

Justin Nicholl
Application Engineer




Six Steps To Optimizing Your Compressed Air System – Step 1: Measure

“To measure is to know – if you cannot measure it, you cannot improve it.”
-Lord Kelvin, mathematical physicist, engineer,and pioneer in the field of thermodynamics.

This is true of most anything. If you want to lose weight, you’re going to need a good scale. If you want to improve your time in the 100 yard dash, you’re going to need a good stopwatch. And if you want to decrease compressed air consumption, you’ll need a good flowmeter. In fact, this is the first of six steps that we can use to help you optimize your compressed air system.

Six Steps To Optimizing Your Compressed Air System

There are various methods of measuring fluid flow, but the most popular for compressed air is thermal mass air flow.  This has the distinct advantage of accurate and instantaneous measurement of MASS flow rate…which is important, because measuring VOLUMETRIC flow rate would need to be corrected for pressure in order to determine the true compressed air consumption.  My colleague John Ball explains this in detail in a most excellent blog on Actual (volume) Vs. Standard (mass) Flows.

So, now we know how to measure the mass flow rate.  Now, what do we do with it?  Well, as in the weight loss and sprint time improvements mentioned earlier, you have to know what kind of shape you’re in right now to know how far you are from where you want to be.  Stepping on a scale, timing your run, or measuring your plant’s air flow right now is your “before” data, which represents Step One.  The next Five Steps are how you get to where you want to be (for compressed air optimization, that is – there may be a different amount of steps towards your fitness/athletic goals.)  So, compressed air-wise, EXAIR offers the following solutions for Step One:

Digital Flowmeter with wireless capability.  This is our latest offering, and it doesn’t get any simpler than this.  Imagine having a flowmeter installed in your compressed air system, and having its readings continually supplied to your computer.  You can record, analyze, manipulate, and share the data with ease.

Monitor your compressed air flow wirelessly over a ZigBee mesh network.

Digital Flowmeter with USB Data Logger.  We’ve been offering these, with great success, for almost seven years now.  The Data Logger plugs into the Digital Flowmeter and, depending on how you set it up, records the flow rate from once a second (for about nine hours of data) up to once every 12 hours (for over two years worth.)  Pull it from your Digital Flowmeter whenever you want to download the data to your computer, where you can view & save it in the software we supply, or export it directly into Microsoft Excel.

From the Digital Flowmeter, to your computer, to your screen, the USB Data Logger shows how much air you’re using…and when you’re using it!

Summing Remote Display.  This connects directly to the Digital Flowmeter and can be installed up to 50 feet away.  At the push of a button, you can change the reading from actual current air consumption to usage for the last 24 hours, or total cumulative usage.  It’s powered directly from the Digital Flowmeter, so you don’t even need an electrical outlet nearby.

Monitor compressed air consumption from a convenient location, as well as last 24 hours usage and cumulative usage.

Digital Flowmeter.  As a stand-alone product, it’ll show you actual current air consumption, and the display can also be manipulated to show daily or cumulative usage. It has milliamp & pulse outputs, as well as a Serial Communication option, if you can work with any of those to get your data where you want it.

With any of the above options, or stand-alone, EXAIR’s Digital Flowmeter is your best option for Step One to optimize your compressed air system.

Stay tuned for more information on the other five steps.  If you just can’t wait, though, you can always give me a call.  I can talk about compressed air efficiency all day long, and sometimes, I do!