Compressed air driven devices are always given a specification for the compressed air flow at a certain pressure. For example, an EXAIR model 1101 Super Air Nozzle has a specified flow of 14 SCFM at 80 PSIG. This means that when this nozzle is operated at 80 PSIG, it will require 14 SCFM of compressed air flow. But what if the force from the nozzle is too high when operated at 80 PSIG and a lower operating pressure is needed?
Thankfully, we can calculate the compressed air flow at a different pressure using the absolute pressure ratio. The absolute pressure ratio says that for any given change in absolute operating pressure, there will be a proportional change in the air consumption of a device. So, what is an absolute pressure?
Put simply, an absolute pressure is the value which you would measure on pressure gauge plus the atmospheric pressure (PSIA, or Pounds per Square Inch Atmospheric). So, our 80 PSIG operating pressure mentioned above is an absolute pressure of 94.5 PSI (80PSIG + 14.5 PSIA). Similarly, if we wanted to determine the compressed air flow at an operating pressure of 60 PSIG, our absolute pressure would be 74.5 PSI (60 PSIG + 14.5 PSIA).
The absolute pressure ratio is a ratio of the new absolute operating pressure (new PSIG + PSIA) compared to the known absolute operating pressure (known PSIG + PSIA). For example, when comparing an operating pressure of 60 PSIG to an operating pressure of 80 PSIG, we will end up with the following ratio:
This means that our absolute pressure ratio in this case is 0.7884. To determine the compressed air flow for the model 1101 Super Air Nozzle at 60 PSIG, we will take this ratio value and multiply it by the known flow value at 80 PSIG. This will yield the following:
Utilizing this formula allows us to truly compare a compressed air powered device at different operating pressures. If we did not use the absolute pressures when comparing compressed air devices at differing pressures, our values would be erroneously low, which could yield to improper compressed air system planning and performance. And, using the absolute pressure ratio allows anyone to make a true comparison of compressed air device performance. If specifications are given at different pressures, performance data can be misleading. But, by using the absolute pressure ratio we can make a more exact evaluation of device operation.
If you have a question about your compressed air device and/or how a change in pressure will impact compressed air flow, contact our Application Engineers. We’ll be happy to help.
I like some better than others, but I don’t believe I’ve ever had bad pizza. That’s why I was pretty excited when I got to talk to a caller from a popular pre-packaged pizza crust maker. When these crusts leave their oven, they spray a coating of seasoned oil on them. This not only flavors, but preserves the quality from the time they make & package them to the time I celebrate life with a tasty slice, right out of my oven.
They were using inexpensive liquid-only nozzles that led to an inconsistent application of the oil…sometimes too much; other times, too little. And, it was always spraying, even in between the individual crusts as they came down the conveyor, leading to wasted oil that had to be cleaned up later.
They were already familiar with our Super Air Nozzles, as they had several Model HP1125SS 2″ High Power Flat Super Air Nozzles in use for blowing off the packages prior to labeling, so the caller asked if we might have a solution for the oil too.
After considering the size of the crust and the distance at which they needed to install the nozzle, they decided to try a Model AF2010SS Internal Mix Flat Fan Pattern No-Drip Atomizing Spray Nozzle. This applies a consistent and even coating of oil, and, by feeding a signal from the oven controls into a solenoid valve in the compressed air supply line, they’ve eliminated the excess spray, leading to savings in material cost and cleanup time.
If you’d like to know more about how EXAIR Atomizing Spray Nozzles can save you time, mess, and liquid, give me a call.
In the world of compressed air blow off solutions, there are a number of options which customers must consider. Should the plant maintenance personnel configure something on-site? Is there a low-cost option available from a catalog warehouse? Or, is there an engineered solution available – and if there is, what does this even mean?
Ultimately, the exercise in comparing these options will help select the option best for the application and best for the company. In order to make these comparisons, we will consider each option based on the following attributes: Force, sound level, safety, efficiency, repeatability, and cost. These are the factors which impact the ability to perform as needed in the application, and effect the bottom line of the company
Blow off applications require a certain amount of force in order to perform the desired task. If the blow off is in a bottling line, for example, we will aim for a lesser force than if blowing off an engine block. But, no matter the application need, we will want to consider the ability of the solution to provide a high force, high impact blow off. Homemade and commercially mass-produced nozzles produce low-to-mid level forces, which translates to a need for more compressed air to complete a task. Engineered nozzles produce high forces, minimizing compressed air use.
Have you ever been to a concert and felt your hearing reduced when you left? This can be the case for personnel in industrial environments with unregulated noise levels. Homemade or non-engineered blow off solutions carry the risk of increased sound levels which are outside of the acceptable noise level limits. EXAIR engineered nozzles, however, are designed to minimize sound level for quiet operation and continual use.
Workplace safety is a serious matter for everyone from shop floor personnel to executive management. Whether you’re working with or near a compressed air operated device, or your making decisions for your company which have to do with the compressed air system, safety is undoubtedly a priority. Unfortunately, homemade and commercially available nozzles normally fail to meet OSHA standards for dead-end pressure requirements (OSHA Standard 29 CFR 1910.242(b)). This means that these solutions can pose a risk of forcing compressed air through the skin, resulting in an embolism which can cause severe harm or even death.
EXAIR nozzles, however, are designed to NEVER exceed dead-end pressure limits and to provide an escape path for airflow in the even the nozzle is blocked. This safety aspect is inherent in ALL EXAIR designs, thereby adding safety to an application when an EXAIR product is installed.
Compressed air is the most expensive utility in any facility. Energy enters as an electrical source and is converted into compressed air through a compressor where up to 2/3 of this energy is lost as heat. The resulting 1/3 of converted energy is then piped throughout a facility as compressed air, where up to 1/3 of the air is lost to leaks. With this in mind, maximizing the efficiency of a nozzle solution becomes imperative. A homemade solution or commercial nozzle does not maximize the use of the compressed air. The result is a need to increase flow or increase pressure, both of which result in higher energy costs.
EXAIR nozzles are designed for maximum force per CFM. This means that any of our nozzles will produce the highest force at the lowest possible compressed air consumption. This, in turn, reduces demand on the compressed air system and allows for a lower energy requirement. Less energy demand means less energy costs, which goes straight to the bottom line of your company.
When installing a nozzle solution, it is important to have the same force and flow from each unit. If a solution needs to be replicated, balanced, or adjusted in any way, having various forces and flows from a homemade setup will induce difficulty and could make changes impossible. Line speed or volume increases may not be possible due to variance in the output flow and forces from homemade setups, but an engineered solution will produce the same output every time. This means you can adjust the nozzles as needed to achieve the perfect solution in your application.
For many customers and businesses, the most important aspect of any solution comes down to cost. Will the solution work? And, how much does it cost? When it comes to a homemade or commercial blow off solution, it may or may not work, and it will have a low purchase cost. But, the purchase price isn’t the whole story when working with compressed air. The real cost of an item is in the operation and use. So, while a homemade solution will be cheap to make and install, it will be EXPOENTIALLY more expensive to operate when compared to an engineered solution. An excellent example is shown above. An open copper tube is compared to an EXAIR model 1102 Mini Super Air Nozzle. The copper tube cost only a few dollars to install, many times less than the EXAIR nozzle, but it costs almost two THOUSAND dollars more to operate in a year. Translation: Install a cheap blow off solution and pay for it in utility costs.
EXAIR nozzles and blow off solutions are engineered for maximum force, lowest possible noise level, OSHA safety compliance, maximum efficiency, and maximum repeatability. These factors allow for options which not only solve application problems, but also do so with the lowest total cost possible. If you have an application in need of a blow off solution, feel free to contact our Application Engineers. We’ll be happy to help. And, if your curious about the benefit of our products in your application, consider our Efficiency Lab. We will test your existing setup next to our recommended EXAIR solution and provide the impact to your bottom line.
EXAIR manufactures a variety of Air Nozzles and Jets to safely, efficiently and effectively blow compressed air. There are many different styles that can best fit specific applications. In this blog, I am going to discuss the EXAIR Air Jets. They are designed to entrain a high volume of ambient air to give a moderate blowing force. Similar to the Air Amplifiers, these miniature devices use very little compressed air to achieve an effective blowing for removing debris, drying parts, or cooling hot products. EXAIR manufactures two different styles, the High Velocity Air Jet and the Adjustable Air Jet.
The Air Jets use a Coanda profile for blowing. The Coanda effect was named after a Romanian aerodynamic pioneer, Henri Coanda who discovered a fluid flow phenomenon. He stated that “a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops” (1). Since air is a fluid, it will react in the same manner. The EXAIR Air Jets create a high velocity air stream along an engineered profile. So, as the air “hugs” the profile, a low pressure is created which will draw in ambient air. The unique design of the Air Jet utilizes a ring jet of compressed air to produce that low pressure at the entrance, entraining the surrounding ambient air. This makes the Air Jet very efficient as it utilizes more ambient air than compressed air.
Depending on the environment or application, the Air Jets come in two types of material; brass and stainless steel. The High Velocity Air Jets use a shim to set a gap. The gap can be changed by installing a different thickness of shim to increase or decrease the blowing intensity. These shims in conjunction with a regulator gives versatility for a wide range of applications. If the desired blowing force needs to be changed for different types of products or flexibility is required “on the fly”, the Adjustable Air Jet would be recommended. It has a micrometer gap indicator to set the desired result. By twisting the plug of the Adjustable Air Jet, you can get output flows from a gentle breeze to a blast. What makes both Air Jets unique is the design. They meet the OSHA standard for noise level and dead-end pressure. If you block the output of the Air Jets, the pressure will not exceed the OSHA safety requirement for dead-end pressure. Also, the inlet and/or outlet can both be ducted for remote positioning.
Our accessories can make the Air Jets easier to use. We have Stay Set Hoses for easy connections and maneuverability. The Stay Set Hoses come in a variety of lengths from 6” (152mm) to 36” (915mm) and once you set the position, the Stay Set Hose will keep the Air Jet stationary even during blowing. You can add a Magnetic Base with the Stay Set Hose and Air Jet to mount the blowing unit right to a metal fixture. It has a 100 lb. (45.5Kg) pulling force to keep the Air Jet from moving until you need to move it. The bases come with a ¼ turn shut-off valve and in a single or dual output configuration. In addition to the above accessories, we also offer a model 9040 Foot Pedal valve for operator control of the duration of blowing with their foot, allowing the use both of their hands.
With the cost to make the compressed air utility being so high, it is important to use it as efficiently as possible. The High Velocity Air Jet and Adjustable Air Jet have the ability to give you effective blowing for removing debris, drying parts, or cooling objects without using a large amount of compressed air. With the accessory items included, you can set up an improved blowing station that will be effective, quiet, and efficient for your operators. The Air Jets are flexible and adaptable to be used in numerous types of blowing applications. If you have any questions about the Air Jets or if you would like to discuss any applications, you can contact an Application Engineer at EXAIR.
What is laminar flow and turbulent flow? Osborne Reynolds popularized this phenomenon with a dimensionless number, Re. This number is the ratio of the inertial forces to the viscous forces. If the inertial forces are dominant over the viscous forces, the fluid will act in a violent and chaotic manner. The formula to determine the Reynolds number is as follows:
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)
The value of Re will determine the state in which the fluid (liquid or gas) will move. If the Reynolds number, Re, is below 2300, then it is considered laminar (streamline and predictable). If Re is greater than 4000, then it is considered turbulent (chaotic and disarrayed). The area between these two numbers is the transitional area where you start to get small eddy currents and velocities in a non-linear direction. When it comes to effective blowing, cleaning and lower noise levels, laminar flow is optimal.
Let’s do a comparison of Reynolds numbers between the EXAIR Super Air Knife and a blower-type air knife. Both products are designed to clean and blow off wide areas like conveyor belts. The EXAIR Super Air Knife is powered by compressed air, and the blower-type air knife is powered by an air blower. The main difference between the two products is the dimension of the slot opening. The Super Air Knife has a gap opening of 0.002″ (0.05mm). It uses the force of the compressed air to “push” it through the small opening to create a strong velocity. A blower does not generate a high force, so the opening of the blower-type air knife has to be larger to overcome any back pressure the opening creates. The gap opening is typically 0.5″ (13mm). From Equation 1 above, the gap opening helps determine the hydraulic diameter, Dh. The hydraulic diameter is an equivalent tube diameter from a non-circular flow area. Since both the Super Air Knives and blower-type air knives have rectangular cross sections, the Dh can be calculated as follows:
Equation 2: Dh = 2 * a * b/ (a + b)
Dh – Hydraulic Diameter (feet or meter)
a – Gap Opening (feet or meter)
b – Gap Width (feet or meter)
If we compare for example a standard 12″ wide air knife, we can calculate the hydraulic diameter, Dh, by using Equation 2:
The exit velocity of the Super Air Knives can be changed by regulating the air pressure. The higher the air pressure, the higher the velocity. The blower type air knives can use a blower with a variable frequency drive (VFD) to change the exit velocity . A reasonable air pressure for the Super Air Knife is 80 PSIG, and the exit velocity is near 540 ft/sec (164 m/s). To equate this to a blower system, the size of the blower will determine the maximum velocity. To do this comparison, I will use the same velocity as the Super Air Knife. With the kinematic viscosity of air, it has a value of 0.000164 ft^2/sec (0.000015 m^2/sec) at 70 deg. F (21 deg C). Now we have all the information for the comparison, and we can now find the Reynolds number from Equation 1:
As you can see from the above calculations, the Super Air Knife has a Reynolds number, Re, below 2300. The flow characteristic is in the region of laminar (predictable and streamline). The blower air knife has a Reynolds number, Re, above 4000. The flow dynamic coming out of the blower-type air knife is turbulent (chaotic and disoriented). To better show the difference in laminar flow and turbulent flow, I have a picture below that shows both states with water as a fluid (being that air is an invisible fluid). Here is an example of water coming out of a drain pipe at Cave Run Lake (first picture below). With the inertial forces much higher than the viscosity of the water, it is in a turbulent state; loud and disorderly. Reynolds number is greater than 4000. The water is traveling in different directions, even upstream. As the water flows into the mouth of the river after the channel (second picture below), the waves transform from a violent mess into a quiet, calm stream flowing in the same direction. This is laminar flow (Re is less than 2300).
With the engineered design of the Super Air Knife, the thin slot helps to create that laminar flow. All the air is moving in the same direction, working together to give a higher force to remove debris. If you have turbulent flow like that of a blower air knife, the noise level is much higher, and the disoriented forces are less effective in blowing. Turbulence is useful for mixing, but horrible for trying to clean or wipe a conveyor belt. If you have any open pipes, drilled pipes or blower-type air knives in your application, you should try an EXAIR product to see the difference. An Application Engineers can help you take advantage of laminar airflow.
There are many ways to blowoff, cool, and/or dry materials. A few of these methods are the drilled pipe, an array of flat nozzles, using a blower driven air knife and the EXAIR Super Air Knife. We’ll examine each in further detail, for blowoff of water after a bottling cleaning operation. Testing was done at 60 PSIG of supply pressure. The blower utilized a 10 hp motor and was a centrifugal type spinning at 18,000 RPM. Sound levels were taken with product not present to test the sound of each of the blowoff types.
Drilled pipe is a common blowoff because it is very inexpensive and easy to make. But drilled pipe performs poorly. The low cost to make the drilled pipe is quickly outpaced by the inefficiency and high compressed air costs. The holes are easily blocked and the noise level is excessive, both of which violate OSHA requirements. Also, the air pattern across the length can be very inconsistent, with areas of low flow and areas of turbulent flow.
Flat air nozzles installed along a length of pipe is another inexpensive option, but it can be a poor performer. The flat nozzles are available in many materials, from many manufacturers. The flat nozzles do offer some efficiencies, but similar to drilled pipe, the operating costs and noise levels are high. Air pattern across the length can be inconsistent with areas of high and low flows, leading to incomplete drying or cooling. Also, many of these nozzles are made from plastic material which breaks or cracks when it it hit which causes additional expense and maintenance to replace broken nozzles.
A blower air knife can prove to be an expensive and noisy option. Typically, the initial purchase price is high. Operating costs are lower than the drilled pipe and flat nozzles and in line with the Super Air Knives. The blowers can be very large and space for two 3″ diameter hoses requires extra mounting space compared to low profile other options. Noise levels are high, at 90 dBA. Annual costs for bearing and filter maintenance can be significant.
EXAIR Super Air Knives performed exceptionally well in removing the water in one pass due to the strong, laminar flow of air. Sound level was low at just 69 dBA, well within OSHA requirements for an hour 8 hour exposure time. Safe operation is assured, as the Super Air Knife design cannot be dead-ended. Maintenance costs are low, as the Super Air Knife has no moving parts to breakdown or wear out.
Ultimately, the Super Air Knife is a low cost way to blowoff, dry, clean and cool.
If you have questions about Super Air Knives, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.
A casting company used a die casting process to make large aluminum panels. In their operation, a two-part die would clamp together and be filled with hot liquid aluminum. Once the panel was formed and cooled, the die would open to release the part. Before the next panel was die casted, they would use a home-made cart to cool and clean the dies. The cooling was done first by spraying water onto the surface, then compressed air was used to dry the dies. When they started to use their home-made cart in their process, they noticed that the air pressure would begin to drop in their facility. Other locations in the plant started having problems with their pneumatic equipment. They were using too much compressed air during the drying period; so, they contacted EXAIR to see if we could help reduce the amount of compressed air to dry the dies.
To explain a little more about the home-made cart, it was made from a 1” square piece of tubing that was bent in a U-shape. The dimension of the cart was about 40” long and 24” high. Across the top was a piece of extruded aluminum spanning the two ends of the U-shape tubing. This portion of the cart would supply the water to the liquid nozzles. The liquid nozzles hung vertically down from the extruded aluminum at designated heights to target certain areas of the dies. The U-shaped square tubing was used to supply the compressed air to the blow-off nozzles. The compressed air inlets were welded onto each end of the 1” square tubing. Across the bottom of the cart, the 1” square tubing had 38 holes that were drilled and tapped to 1/8” NPT (19 tapped holes on each side). The blow-off nozzles were 1/8” pipes with the ends smashed (reference picture below). They were made to different lengths to get as close to the die for maximum blowing force. The entire home-made assembly was attached to a robotic fixture with a cam to move the large cart between the dies. In applications using “smashed” pipes, they are very easy and inexpensive to make. But, as this customer found out, they use way too much compressed air and they are not as effective in blowing-off or drying.
The customer above was limited to modifications to the home-made cart. It was already configured with the robot features and cam to hit the targeted areas. So, I recommended the model HP1126, 1” High Power Flat Super Air Nozzle. It has a 1” wide air stream that is very similar to the flow pattern of the 1/8” smashed pipe. But unlike the smashed pipe design, the model HP1126 nozzle can accomplish so much more. One of the biggest differences is that the EXAIR nozzles use much less compressed air. (The initial reason for contacting EXAIR). With the engineered design of the nozzle, it can entrain large amounts of ambient air which means that less compressed air is required. For a 1/8” NPT smashed pipe, it can use close to 70 SCFM of air at 80 PSIG – each!
The model HP1126 only requires 17.5 SCFM at 80 PSIG. That is a difference of 52.5 SCFM per nozzle. With 38 nozzles being used on this home-made cart, that equates to a total savings of 1,995 SCFM of compressed air. By simply replacing the 1/8” smashed pipe to a model HP1126 with a shorter nipple, their facility was able to save much compressed air and maintain the pneumatic requirements in the other work areas.
The customer was extremely happy with the air savings, but they asked about the amount of force that the model HP1126 can supply. It was important in their process to remove any residual water from the dies. The reason for the blow-off pipes to be so close to the die was to try and increase the blowing force. The best way that I could explain to them was by using an example of a garden hose. (Reference a blog by Neal Raker “Sometimes Back Pressure is Good; Sometimes it is Bad“). The garden hose is attached to a spigot outside your house. As you open the spigot to supply water through the hose, the water will flow out of the hose at a slow velocity; not very strong. When you place your thumb partially over the end of a garden hose, you restrict the flow and increase the force. Now, you can reach the second-floor windows of your house to clean. With a lack of restriction at the end of the pipes, the air pressure will drop quickly as it travels through the long square tube and through the 1/8” pipe extensions. By the time the compressed air reaches the blow-off site, the pressure is much lower; thus, reducing the effectiveness of removing the water.
The EXAIR nozzles work like your thumb on the hose. The usable pressure is increased at the HP1126 nozzle, instead of a point much further upstream. By increasing the pressure at the point-of-use, the effective velocity and force is much stronger. In addition to this, they can now move the nozzles away from the die surface; in case of any “hiccups” in moving the cart in and out of the dies and eliminating any marring of the surfaces.
Once they installed the 38 pieces of the model HP1126 nozzles onto their cart, the first thing that they noticed was the amount of noise reduction. The model HP1126 only has a noise level of 82 dBA at 80 PSIG, compared to a noise level of an open pipe which is over 100 dBA. By replacing the flattened nozzles with the EXAIR nozzles, this company was able to…
1. reduce air consumption
2. keep the other areas of the plant operating by conserving compressed air at this location
3. reduce the noise level and
4. increase the effective blowing force
If you find that by using your blow-off/drying system, your pneumatic machines under-perform, or the low-pressure alarms are triggered, or you have to turn on an auxiliary compressor, you should contact an Application Engineer at EXAIR to see if we can optimize your compressed air devices. These EXAIR engineered nozzles can remove many issues in your system as it did with the casting company above.