Reduce Sound Levels With Engineered Compressed Air Products

A while back, I had the pleasure of assisting a customer with selection and implementation of our Super Air Nozzles, to replace open-ended blow offs on their machine tools. They installed the Super Air Nozzles after shutdown one afternoon. When he came in to work the next day (he arrived after production started), he thought there was a major problem in the shop, because (as they say in the movies right before something bad happens) “it was quiet…too quiet.” Turns out that, even though the goal was to reduce air consumption, they also reduced the sound level of the blow offs to an unexpected degree.

The copper tube used to have a crimped end that was aimed at the part in the chuck. They simply cut it off and used a compression fitting to install the Super Air Nozzle.

Another time, a metal stamping plant tried out our Model 1122 2″ Flat Super Air Nozzle on a stamping machine, using a Stay Set Hose to replace the copper tubing that was used to eject parts from the platen. They did the switch in the middle of the day…the operator at the adjacent machine noticed the dramatic noise level drop and came over to see what was wrong. Then he asked when they were getting one for HIS machine.

This loud & inefficient copper tubing blowoff was just Model 1122 2″ Flat Super Air Nozzle (and a Stay Set Hose) away from being quiet and efficient.

Both of these solutions originated with calls to discuss ways to reduce compressed air consumption costs. The fact that noise levels went down so dramatically just added to the benefits of using engineered compressed air products from EXAIR. If you’d like to find out how to make your electric bill – and your shop noise level – go down, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Dead Serious About Dead End Pressure and Chip Guarding – OSHA 1910.242(b)

Compressed air is a very versatile utility that can be used for applications in cooling products to cleaning off workspaces and products. That is where OSHA 1910.242(b) comes into play; this OSHA standard states that compressed air used for cleaning shall not be used except were reduced to less than 30 psi and then only with effective chip guarding and personal protective equipment. This standard is in place because in the event a dead end occurs, the static pressure at the main orifice can potentially force the high pressure air into someone’s bloodstream and cause an air embolism, which if left untreated can impede the flow of blood in the body and lead to a fatality.

Keeping that in mind there are two ways you can go about these cleaning applications and still stay in compliance with the OSHA standard. The first way is to regulate the air pressure in your pipe down to below 30 psig. But for the majority of applications this is not an effective solution as pressure does equate to the amount of force that can be produced from the system. The second solution is to use a nozzle that is engineered in a way the it cannot be dead ended. This means that the nozzle is designed in a way that no matter how hard you try the air coming out of the nozzle will be ejected into the atmosphere and not through skin.

The fins of the Super Air Nozzle allow air to escape and prevent dead-ending the nozzle.

Take EXAIR’s Air Nozzles for example, the fins and orifice placement are designed in a way that allows air escape air into the atmosphere. Once air has exited an orifice into atmospheric conditions the pressure becomes 0 psig but retains the velocity and higher volume from the higher compressed air inlet pressure which produces force.

Model 1210 Soft Grip Safety Air is fitted with an EXAIR Super Air Nozzle. We can also supply it with a Rigid Extension and Chip Shield (right).

In addition, OSHA 1910.242(b) also talks about the use of effective chip guarding, which simply means some method or equipment shall be installed that prevents particles from flying back and hitting the operator. If you look EXAIR’s Safety air guns you will notice that we offer Chip Shields. By simply adding “-CS” to the end of a part number for a Safety Air Gun you can help prevent injuries from flying particles in blow off applications.

If you have any questions or want more information on compressed air safety and OSHA related standards. Give us a call, we have a team of application engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Boundary Layer: Laminar and Turbulent flow

Fluid mechanics is the field that studies the properties of fluids in various states.  Fluid dynamics studies the forces on a fluid, either as a liquid or a gas, during motion.  Osborne Reynolds, an Irish innovator, popularized this dynamic with a dimensionless number, Re. This number determines the state in which the fluid is moving; either laminar flow, transitional flow, or turbulent flow.  For compressed air, Re < 2300 will have laminar flow while Re > 4000 will have turbulent flow.  Equation 1 below shows the relationship between the inertial forces of the fluid as compared to the viscous forces. 

Equation 1: 

Re = V * Dh / u

Re – Reynolds Number (no dimensions)

V – Velocity (feet/sec or meters/sec)

Dh – hydraulic diameter (feet or meters)

u – Kinematic Viscosity (feet^2/sec or meter^2/sec)

To dive deeper into this, we will need to examine the boundary layer.  The boundary layer is the area that is near the surface of the object.  This could refer to a wing on an airplane or a blade from a turbine.  In this blog, I will target pipes, tubes, and hoses that are used for transporting fluids.  The profile across the area (reference diagram below) is a velocity gradient.  The boundary layer is the distance from the wall or surface to 99% of the maximum velocity of the fluid stream.  At the surface, the velocity of the fluid is zero because the fluid is in a “no slip” condition.  As we move away from the wall, the velocity starts to increase.  The boundary layer distance measures that area where the velocity is not uniform.  If you reach 99% of the maximum velocity very close to the wall of the pipe, the air flow is turbulent.  If the boundary layer reaches the radius of the pipe, then the velocity is fully developed, or laminar. 

Boundary Layer Concept

The calculation is shown in Equation 2.

Equation 2:

d = 5 * X / (Re1/2)

d – Boundary layer thickness (feet or meter)

X – distance in pipe or on surface (feet or meter)

Re – Reynolds Number (no dimensions) at distance X

This equation can be very beneficial for determining the thickness where the velocity is not uniform along the cross-section.  As an analogy, imagine an expressway as the velocity profile, and the on-ramp as the boundary layer.  If the on-ramp is long and smooth, a car can reach the speed of traffic and merge without disrupting the flow.  This would be considered Laminar Flow.  If the on-ramp is curved but short, the car has to merge into traffic at a much slower speed.  This will disrupt the flow of some of the traffic.  I would consider this as the transitional range.  Now imagine an on-ramp to be very short and perpendicular to the expressway. As the car goes to merge into traffic, it will cause chaos and accidents.  This is what I would consider to be turbulent flow.      

EXAIR Digital Flowmeter

In a compressed air system, similar things happen within the piping scheme.  Valves, tees, elbows, pipe reducers, filters, etc. are common items that will affect the flow.  Let’s look at a scenario with the EXAIR Digital Flowmeters.  In the instruction manual, we require the meter to be placed 30 pipe diameters from any disruptions.  The reason is to get a laminar air flow for accurate flow measurements.  In order to get laminar flow, we need the boundary layer thickness to reach the radius of the pipe.  So, let’s see how that number was calculated.  

Within the piping system, high Reynold’s numbers generate high pressure drops which makes the system inefficient.  For this reason, we should keep Re < 90,000.  As an example, let’s look at the 2” EXAIR Digital Flowmeter.  The maximum flow range is 400 SCFM (standard cubic feet per min).  In looking at Equation 2, the 2” Digital Flowmeter is mounted to a 2” Sch40 pipe with an inner diameter of 2.067” (52.5mm).  The radius of this pipe is 1.0335” (26.2 mm) or 0.086 ft (0.026m).  If we make the Boundary Layer Thickness equal to the radius of the pipe, then we will have laminar flow.  To solve for X which is the distance in the pipe, we can rearrange the terms to:

X = d * (Re)1/2 / 5 = 0.086ft * (90,000)1/2 / 5 = 5.16 ft or 62”

If we look at this number, we will need 62” of pipe to get a laminar air flow for the worse-case condition.  If you know the Re value, then you can change that length of pipe to match it and still get valid flow readings.  From the note above, the Digital Flowmeter will need to be mounted 30 pipe diameters.  So, the pipe diameter is 2.067” and at 30 pipe diameters, we will need to be at 30 * 2.067 = 62”.  So, with any type of common disruptions in the air stream, you will always get good flow data at that distance. 

Why is this important to know?  In many compressed air applications, the laminar region is the best method to generate a strong force efficiently and quietly.  Allowing the compressed air to have a more uniform boundary layer will optimize your compressed air system.  And for the Digital Flowmeter, it helps to measure the flow correctly and consistently.  If you would like to discuss further how to reduce “traffic jams” in your process, an EXAIR Application Engineer will be happy to help you.

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

Efficiency Lab Leads To Big Savings

EXAIR Corporation manufactures quiet, safe, and efficient compressed air products for industry. We want our customers to get the most out of our products, and, in turn, their compressed air systems. To do that, we offer a unique service called the EXAIR Efficiency Lab. Here’s how it works:

  • An Application Engineer can arrange to have your existing compressed air device(s) sent in to our facility.
  • We’ll use our calibrated test equipment to measure the compressed air consumption, sound level, and force applied of those devices.
  • You’ll receive a detailed test report, along with our recommendations to implement an efficient, quiet, and safety compliant solution.
  • We’ll even send your tested device(s) back to you, at no charge, if you wish.

I recently had the pleasure of conducting just such a test on some air guns.  The caller was the Environmental Health & Safety Director for a plastics manufacturer.  The main concern was safety compliance…a recent audit had shown that some workstations were using handheld blowoff devices that did not comply with OSHA standard 1910.242(b), which limits dead end pressure of compressed air products used for cleaning to 30psi.

After discussing their typical uses for these (and other) air guns, they sent in a couple for testing.  Here’s what we found out:

“Thumb guns” are especially popular for blowoff because of their compact size, ergonomic design. and low price.

The air gun with the 7″ straight extension (top) is a “textbook” example of non-compliance with OSHA standard 1910.242(b).  Because it has an open-end discharge with no relief path, this one could cause an air embolism if it were inadvertently dead-ended into the operator’s skin – a potentially fatal condition.  It also uses a considerable amount of compressed air, and is quite loud.  At 80psig supply pressure:

  • Compressed air consumption is 40.7 SCFM
  • Noise level is 95.5dBA
  • Force applied, at a distance of 12″, is 13oz

For comparison’s sake, EXAIR Model 1210-6 Soft Grip Safety Air Gun is fitted with our Super Air Nozzle, on the end of a 6″ rigid extension:

  • Compressed air consumption is 14 SCFM
  • Sound level is 74dBA
  • Force applied, at a distance of 12″, is 13oz…same as theirs.
Model 1210 Soft Grip Safety Air is fitted with an EXAIR Super Air Nozzle. We can also supply it with a Rigid Extension and Chip Shield (right).

The other one is OSHA compliant (it can’t be dead-ended…the cross-drilled hole provides a relief path, but it was still pretty inefficient and loud.  At our standard test pressure of 80psig:

  • Compressed air consumption is 30.8 SCFM
  • Noise level is 94.8dBA
  • Force applied, at a distance of 12″, is 16.9oz

Although the force generated by the Model 1210 Soft Grip Safety Air Gun isn’t quite as high as theirs, it’s still our recommendation here.  Oftentimes, the flow and velocity generated by the engineered Super Air Nozzle is more than capable of meeting the needs of the typical blow off applications these types of air guns are used in.

EXAIR Efficiency Lab testing proves that replacing these air guns with our Soft Grip Safety Air Guns (or at least replacing the tips with EXAIR Super Air Nozzles…we also have adapters for that) will result in compressed air savings of 66% and 55%, respectively, and lower sound levels to within OSHA standard 1910.95(a) limits:

All EXAIR Soft Grip Safety Air Guns comply with these limits for 8 hour exposure.

If you’d like to know more about the efficiency & safety (or lack thereof) of your current air blow off devices, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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