Understanding Noise: Sound Power Vs. Sound Pressure

Sound Power and Sound Pressure have been covered a few other times here on the EXAIR Blog. Once here by Brian who made the visual correlation in regards to a speaker and a musical instrument. And here by Russ who breaks down how you calculate sound power level with the below equation!
Sound Power Equation
too lou Sound Power Level Equation
All machines generate sound when they are in operation. The propagated sound waves cause small changes in the ambient air pressure while traveling. A sound source produces sound power and this generates a sound pressure fluctuation in the air. Sound power is the cause of this, whereas sound pressure is the effect. To put it more simply, what we hear is sound pressure, but this sound pressure is caused by the sound power of the emitting sound source. To make a comparison, imagine for example a simple light bulb. The bulb’s power wattage (in W) represents the sound power, whereas the bulb’s light intensity represents the sound pressure.
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Light Bulb
Sound power does not generally depend on the environment. On the contrary, the sound pressure depends on the distance from the source and also on the acoustic environment where the sound wave is produced. In the case of indoor installations for example, sound pressure depends on the size of the room and on the sound absorption capacity of the surfaces. For instance, say the room walls don’t absorb all the sound but reflect parts of it, then the sound pressure will increase due to the so called reverberation effect. (reverberation time is broadly defined as the time it takes for the sound pressure to reduce by 60 dB after the sound emitting source has been shut off). 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. Jordan Shouse Application Engineer Send me an email Find us on the Web  Like us on Facebook Twitter: @EXAIR_JS Light Bulb image courtesy of  josh LightWork  Creative Commons License

The Soft Grip Safety Air Gun for OSHA Compliance

Compressed air has many different uses ranging from simple cooling and blow off applications all the way to operating machine cylinders and robotics. One of the most common uses is for simple cleaning; whether its cleaning off a work station or blowing off personnel it can’t be denied that air powered cleaning is very useful. But if the Occupational Safety & Health Administration (OSHA) regulations are not followed it can also be unsafe.

Open-ended blow offs can inadvertently be dead ended (the airflow outlet can be completely blocked), when this happens if the pressure is to high an air embolism can form in an individuals bloodstream. Blowing something off with air can result in airborne particulate traveling at a high velocity that can become embedded into your skin or in your eye.

With all that being said this is where the safety air guns step into the spotlight! It’s pretty easy to make a safety air gun that complies with the dead-end pressure regulation; just give the air another path to take when the outlet is blocked. The most common solution found is a cross drilled nozzle which allows the air to escape when the end is blocked. Generally the problem with this design is that the nozzles can be very loud and inefficient. In most cases these nozzles have paid attention to the dead end problem but ignored the noise level exposure safety issue and completely ignored compressed air efficiency. 

With EXAIR’s Super Air Nozzles you get both the added benefit of being safe, quiet and efficient. Our engineered designed air nozzles are commonly installed onto a Soft Grip Safety Air Gun to make an ergonomic, safe, and quiet Safety Air Gun. These can also have a  Chip Shield added to help prevent particles from flying back and hitting the user. The Soft Grip Safety Air Gun can also be coupled with a pipe extension from 6” to 72”; you can also add one of our Stay Set Hoses 6” in length to 36”.

Soft Grip Safety Air Gun with Stay Set Hose. eg. 1210-6SSH

Here are a few examples of the Soft Grip Safety Air Guns in our product line:

Cody Biehle
Application Engineer
EXAIR Corporation
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Benefits of Air Nozzles Replacing Coolant Lines used for Air

Over the years, EXAIR has come across many different types of blow-off devices.  We have seen copper tubes, pipes with crushed ends, fittings with holes drilled into them, and modular flex lines.  For compressed air use, these are very dangerous and very inefficient.

A plastic machining center was looking for a better way to blow compressed air.  They were using modular flex lines, similar to Loc-line, which are mainly designed for spraying coolant.  They had 14 blow-off lines in their plant that were about 18” (457mm) long and operated 8 hours a day at 40 PSIG (2.8 bar).  They liked the positioning feature of the flex line, but they could tell by the loud noises that they were wasting compressed air.  So, they contacted EXAIR.

When EXAIR started to manufacture compressed air products in 1983, we created a culture in making high quality products that are safe, effective, and very efficient.  With our Super Air Nozzles, we engineered a way to entrain the ambient air to add mass to the air stream to use less compressed air with a strong force.  This is done by the Venturi method.  We create a high velocity which will make a low pressure at the exit.  The surrounding air is drawn into the compressed air stream increasing efficiency.  We also engineered fins to support OSHA compliance in noise levels and dead-end pressure.  So, if your skin comes in contact with an EXAIR nozzle, the end will not be able to be blocked and allow air to penetrate the skin membrane; even above 30 PSIG (2 bar).  I went over the cost savings and safety solutions that EXAIR’s products could give.

EXAIR Super Air Nozzle entrainment

Since the modular flex lines had a ¼” (6mm) opening, I recommended the model 1100 Super Air Nozzle with a Stay Set Hose.  This recommendation is from experience with these types of blow-off devices.  The Stay Set Hoses will give them that possibility of manually adjusting and re-adjusting the Super Air Nozzles.  The hoses have a “memory” function and will not creep or droop until you physically move it.  They work well to direct air flows at specific target areas like the flex lines above.  For the company above, I recommended the model 1100-9218 which is a model 1100 Super Air Nozzle with an 18” (457mm) long Stay Set Hose.  It was easy to remove the flex line and replace it with a safer and more efficient product

Model 1100-9218

Now, let’s look at the savings.  The Super Air Nozzle with the 18” Stay Set Hose cost $92.00 each.  The flex line is generally around $10.00 each.  But this is not the total cost of ownership.  As an efficiency comparison, the model 1100 Super Air Nozzle will only use 8 SCFM (227 SLPM) of compressed air at 40 PSIG (2.8 bar); and, the noise level is reduced to 70 dBA for each nozzle.  At 40 PSIG (2.8 bar), the flex line had a noise level of 97 dBA and an air usage of 19 SCFM (538 SLPM).

For the annual savings and the payback period, I will look at the electrical cost.  (Since the Super Air Nozzle is using less compressed air, the maintenance and wear on your air compressor is reduced.)

  • The air savings is calculated from the difference in air usage; 19 SCFM for flex line – 8 SCFM for Super Air Nozzle = 11 SCFM savings per blow-off device.
  • With 14 flex lines, the total compressed air savings will be 11 SCFM * 14 = 154 SCFM.
  • To get into the cost, an air compressor can produce 5.36 SCFM/KW of electricity at a cost of $0.10/KWh.  For an annual savings, we have the figures from the information above; 8 hours/day * 250 days * 154 SCFM * $0.10/KWh * 1KW/5.36 SCFM = $5,746.27/year.
  • For a payback period, the model 1100-9218 has a price of $92.00 each, or $1,288.00 for 14 systems.  The flex lines were $10.00 each, or $140.00 total.  The payback period will be ($1,288 – $140) / ($5,746.27/year) * (12 months/year) = 2.4 months.  Wow, what a savings!

Not all blow off devices are the same.  With the customer above, they were able to cut their noise levels, remove the dead-end pressure concerns, and save $5,746.27 a year in compressed air.  If your company decides to select an unconventional way to blow off parts without contacting EXAIR, there can be many hidden pitfalls; especially with safety.  Besides, if you can save your company thousands of dollars per year as well, why go with a non-standard nozzle?  If you are using compressed air for blowing, cooling, cleaning or moving material; you should contact an Application Engineer at EXAIR.  What do you have to lose?

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

Reduce Sound Levels In Less Than A Minute

Okay, I will admit, the title may be a tad bit leading.  The fact is, it can be done.  I speak to customers almost daily who are struggling with the noise levels produced from open pipe blowoffs.  With Noise Induced Hearing Loss (NIHL) a significant problem among manufacturing workers, reducing the noise form compressed air can be a simple solution and contribute toward reducing overall noise exposure levels. Many of these calls and emails revolve around reducing these exact noise levels, sometimes the open pipes have existing threads on them to install the solution immediately.

To reduce these noise levels, we need to simply reduce the amount of energy that is being expelled through the pipe. How do we do this you might ask?  The use of an air nozzle will reduce the energy being dispersed from an open pipe.  This will result in lower air consumption as well as lower sound levels while actually increasing velocity as the pipe will maintain higher operating pressures. Be cautious about the air nozzle you choose, however, they are not all created equal. EXAIR’s engineered air nozzles are among the quietest and most efficient air nozzles available.

Family of Nozzles

What size pipes can we fit nozzles to?  That’s a great question.  We have nozzles that range from a 4mm straight thread all the way up to 1-1/4″ NPT thread.  This also includes nearly any size in between especially the standard compressed air piping sizes.  For instance, a 1/4″ Sched. 40 pipe that has 1/4″ MNPT threads on it can easily produce over a 100 dBA noise level from 3 feet away.  This can easily be reduced to below 80 dBA from 3′ away by utilizing one of our model 1100 Super Air Nozzles.  All it takes is a deep well socket and ratchet with some thread sealant.

This doesn’t just lower the sound level though, it reduces the amount of compressed air expelled through that open pipe by creating a restriction on the exit point.  This permits the compressed air to reach a higher line pressure causing a higher exit velocity and due to the engineering within the nozzle, this will also eliminate dangerous dead-end pressure and complies with OSHA standard 29 CFR 1910.242(b).

Easy Install

All in all, a 30-second install can make an operator’s work station considerably quieter and potentially remove the need for hearing protection.  If you would like to discuss how to lower noise levels in your facility, contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF