EXAIR Compliance with OSHA 1910.242(b)

OSHA Standard 1910.242(b) discusses the use of compressed air for cleaning and blowoff. It states that the use of compressed air for cleaning purposes is prohibited if the dead-ended pressure exceeds 30 psig. This phrase means the downstream pressure of the air nozzle or gun, used for cleaning purposes, will remain at a pressure level below 30 psig for all static conditions. In the event that dead ending occurs, the static pressure at the main orifice shall not exceed 30 psi. If it does exceed this pressure, there is a very high potential for it to create an air embolism. An air embolism, left untreated, can quickly impede the flow of blood throughout the body. This can lead to stroke, heart attack, and sometimes death.

So making sure you are in compliance with 1910.242(b) is truly a life and death situation. Most people believe that lowering the pressure to the blow off device is the only method to keep their operators safe from an air embolism. However this can become a problem when you really need the force of greater than 30 PSIG to complete your operation. We at EXAIR want to give you the flexibility to run at any pressure with out the risk of building that 30 PSI of dead-end pressure! We do this with our line of Intelligent Compressed Air® nozzles! All of EXAIR’s Air Nozzles are designed so that the flow cannot be dead-ended. The fins on the Super Air Nozzles are not only useful in amplifying the force by drawing in ambient air, but they also prevent an operator from completely obstructing the airflow.

Another great example of this is our 2″ Flat super air nozzle. The design not only allows the nozzle to amplify the air flow in the blast of air, the over hang will not let the dead end pressure build as it can escape around the edges and bottom!

2″ Flat Super Air Nozzle

If you’ve got questions about compressed air safety or have an existing blowoff in place that does not adhere to this OSHA directive, give us a call. We’ll be sure to recommend a solution that will keep your operators and wallets safe!

Jordan Shouse
Application Engineer

Send me an Email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_JS

“It’s Not Rocket Science”, or How Compressed Air Has Straightforward Applications In Aerospace

On the submarine I served on, many of us used math, specific to our jobs. Torpedo (and missile) fire control, navigation, reactor operations…even meal cooking…involved certain formulas to accomplish particular tasks. One formula we all knew and kept near & dear to our hearts, though, was:

Number of surfaces = Number of dives

And those who fly aircraft and spacecraft, in – and out of – the atmosphere, have a similar formula:

Number of landings = Number of takeoffs

While this certainly requires a great deal of skill of the operators (as does diving and surfacing a submarine), it also takes a great deal of technical acumen in the engineering and construction of those aircraft & spacecraft (and warships). Terms like “aircraft grade” inspire a high degree of confidence in the integrity of materials, and rightly so – the quality standards that manufacturers and suppliers are held accountable to are stringent and inviolate. That’s why aerospace professionals need reliable, durable, and effective equipment to do their jobs.

EXAIR Corporation has been providing this kind of equipment to the aerospace industry (and others) since 1983. Here are some examples of the applications we’ve worked with “steely eyed missile men” to solve:

  • A jet engine manufacturer makes a titanium assembly consisting of a honeycomb shaped extrusion bonded to a rigid sheet. The cells of the honeycomb are only 1/8” wide, and 3/8” deep. After fabrication, they’re washed & rinsed, and the tiny cells tend to hold water. They would invert & tap the assembly to try to get the water out, but that wasn’t always effective and occasionally led to damaging the assembly. To reduce the chance of damage (and loss) of an assembly, they built a cleaning station, using EXAIR Model HP1125 2” High Power Super Air Nozzles and Model 9040 Foot Pedals, for hands-free control of the high force blow out of the honeycomb cells. The results were increased production, decreased defects, and lower labor costs.
  • A machine shop makes composite material parts for the aerospace industry. Static charge would build up, causing the shavings to cling to most of the surfaces inside the machine. The vacuum system was unable to overcome the force of the static charge to remove it, so they called EXAIR. Our expertise in static elimination led to the specification of a Model 8494 Gen4 Stay Set Ion Air Jet System to direct ionized air onto the tool during cutting. This eliminated the static as it was generated on the shavings, allowing the vacuum system to perform as advertised. Not only did it make for a cleaner work station, the air flow provided cooling for the cutting tool, improving performance & extending life.
  • If a company works with metal parts, there’s a decent chance they operate a welding machine, and those things make smoke & fumes that, at best, are a nuisance, and at worst, are toxic. An airplane repair shop that has to weld in tight spaces needed a convenient, portable, compact way to evacuate the welding smoke and fumes. They chose a Model 120024 4” Super Air Amplifier. They’re capable of pulling in over 700 SCFM, and with a sound level of only 73dBA and lightweight aluminum construction, they’re an ideal fit for this application.
  • Certain satellites have components whose batteries must be fully charged to ensure that everything works just right. Because of the heat that charging generates, they couldn’t be charged with the spacecraft on the launch pad without cooling. Conventional methods of providing cold air (refrigerant based or cold water chillers) are too bulky, so they instead use a Model 3230 Medium Vortex Tube, capable of providing 2,000 Btu/hr worth of cooling air flow. This enables them to charge the battery until just prior to launch, making sure the batteries are as fully charged as possible, prior to deployment.
  • While the lion’s share of Vortex Tube applications involve the use of their cold flow, a number of folks do use the hot air flow, with great success. A major material supplier to the aircraft & aerospace industry makes a flexible, porous strand of material that, after fabrication, passes through a wash tank prior to cutting to size. They wanted to speed up the drying time, but it was impractical to use electrically powered hot air blowers or heat guns. By using an EXAIR Model 3275 Large Vortex Tube set to a 70% Cold Fraction, they’re able to blow a little over 22 SCFM of 220°F air onto the strand, which effectively dries it to their specification, quickly & safely.
These are some of the EXAIR Intelligent Compressed Air Products used in the aerospace industry.

Exacting jobs call for safe, efficient, and reliable tools. Even if your job “isn’t rocket science”, the value of the right tool cannot be stressed enough. If you use – or want to use – compressed air for such a task, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook

“Math Wall” image courtesy of João Trindade, Creative Commons License

How to Best Apply Vortex Tube Cooling

So, you have found yourself with a little bit of a conundrum. You need to cool a part but don’t know where to start and there are so many different options to choose from. In most cases when it comes to cooling with compressed air there are two different paths you can take. First is using a large volume of air at room temperature to blow across the surface area of the product. The other option is to use cold air from a vortex tube to drop the part’s temperature. In most case a large volume of air can be used to cool things down to relatively cooler temperatures; think cooling a cup of coffee using your breath. The issue you run into is when the temperature of the room air gets closer to the temperature you want to achieve in the end. In other words, when the temperature difference between your cooling air and your desired end temperature is small there is less cooling taking place with that same volume of air.

Mini Spot Cooler cooling down a bit used in milling plastic

This can be explained by looking at the cooling power formula:

Btu/hr = 1.0746*(CFM)*(Delta T)

In this case the Delta T is the difference between the temperature that you want to cool the product down to and the temperature of the air. This means the smaller the delta T is the higher the CFM flow will need to be to counteract the effect of the temperatures are so close to one another. Here are some examples of cooling a product and you are providing 1000 CFM of air to cool it.

Btu/hr = 1.0746*(1000 CFM)*(150F – 130F)

                Btu/hr = 21,492 Btu/hr

Btu/hr = 1.0746*(1000 CFM)*(150F – 100F)

                Btu/hr = 53,730 Btu/hr

As you can see the closer the Delta T is to 0 the less Btu/hr you get. Getting this kind of CFM flow is easy if you use something like EXAIR’s Super Air Knife or Super Air Amplifier. These systems take a small amount of compressed air and entrain the surrounding ambient air to increase the volume to a large blast. Take a look at model number 120022 which is the 2” Super Air Amplifier, this unit can produce 1,023 CFM while only using 15.5 CFM at 80 psig. But when you get close to cooling the temperature down to that room temperature or below it gets much harder; which only means that the temperature of the air being used to cool needs to be dropped. Dropping the air temperature can only be accomplished by using outside means like air coolers or in this case EXAIR’s Vortex Tubes and Spot Coolers.

EXAIR Air Amplifiers use a small amount of compressed air to create a tremendous amount of air flow.

Vortex Tubes and Spot coolers have some limitations. Generally they are not thought of products that produce large volumes of air (even though we make them up to 150 SCFM). And they are best suited for smaller areas of cooling, spot cooling, if you will. However, EXAIR Vortex Tubes do have one key feature that can help compensate for the lack of volume. LOW TEMPERATURE! The vortex tube can produce temperatures lower than 0F while stile retaining a good portion of air volume from the inlet.

Sub-zero air flow with no moving parts. 3400 Series Vortex Tubes from EXAIR.

For example, let’s look at model number 3240 running at 100 psig with 70% of the air from the inlet exiting the cold side (aka 70% cold fraction). At 100 psig the 3240 will use 40 SCFM at the air inlet and will have a temperature drop of 71F. If the compressed air has a temperature of 70F that means you will be seeing a temperature of -1F. Also, when using the 70% cold fraction you will see 28 SCFM of cold air flow. Now let’s plug those numbers into the cooling power formula.

 Btu/hr = 1.0746*(28 CFM)*(150F + 1F)

                Btu/hr = 4543 Btu/hr

As you can see, using a small amount of compressed air you can still net you a good amount of cooling if the temperature is lower. All in all, the best option for cooling products down to temperatures that are above ambient temperatures is something that can produce a large volume of air. For small areas that require cooling the product down to temperatures to ambient temperature and below, use EXAIR’s Vortex Tube.

If you have questions about our Air Amplifiers and Vortex Tubes, or would like to talk about any of the quiet EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR or any Application Engineer.

Cody Biehle
Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook

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