Tag: compressed air quality

Discharge of Air Through an Orifice

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My Application Engineer colleagues and I frequently use a handy table, called Discharge of Air Through an Orifice. It is a useful tool to estimate the air flow through an orifice, a leak in a compressed air system, or through a drilled pipe (a series of orifices.) Various tables and online calculators are available. As an engineer, I always want to know the ‘science’ behind such tables, so I can best utilize the data in the manner it was intended.

DischargeThroughAnOrifice

The table is frequently found with values for pressures less than 20 PSI gauge pressure, and those values follow the standard adiabatic formula and will not be reviewed here.  The higher air pressures typically found in compressed air operations are of interest to us.

For air pressures above 15 PSI gauge the discharge is calculated using by the approximate formula as proposed by S.A. Moss. The earliest reference to the work of S.A. Moss goes back to a paper from 1906.  The equation for use in this table is-EquationWhere:
Equation Variables

For the numbers published in the table above, the values were set as follows-

                  C = 1.0,      p1 = gauge pressure + 14.7 lbs/sq. in,    and T1 = 530 °R (same as 70 °F)

The equation calculates the weight of air in lbs per second, and if we divide the result by 0.07494 lbs / cu ft (the density of dry air at 70°F and 14.7 lbs / sq. in. absolute atmospheric pressure) and then multiply by 60 seconds, we get the useful rate of Cubic Feet per Minute.

The table is based on 100% coefficient of flow (C = 1.0)  For well rounded orifices, the use of C = 0.97 is recommended, and for very sharp edges, a value of C = 0.61 can be used.

The table is a handy tool, and an example of how we use it would be to compare the compressed air consumption of a customer configured drilled pipe in comparison to that of the EXAIR Super Air Knife.  Please check out the blog written recently covering an example of this process.

If you would like to talk about the discharge of air through an orifice 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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Intelligent Compressed Air: How to Develop a Pressure Profile

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An important part of operating and maintaining a compressed air system is taking accurate pressure measurements at various points in the compressed air distribution system, and establishing a baseline and monitoring with data logging.  A Pressure Profile is a useful tool to understand and analyze the compressed air system and how it is functioning.

Pressure Profile 1
Sample Pressure Profile

The profile is generated by taking pressure measurements at the various key locations in the system.  The graph begins with the compressor and its range of operating pressures, and continues through the system down to the regulated points of use, such as Air Knives or Safety Air Guns.  It is important to take the measurements simultaneously to get the most accurate data, and typically, the most valuable data is collected during peak usage periods.

By reviewing the Pressure Profile, the areas of greatest drop can be determined and the impact on any potential low pressure issues at the point of use.  As the above example shows, to get a reliable 75 PSIG supply pressure for a device or tool, 105-115 PSIG must be generated, (30-40 PSIG above the required point of use pressure.)  As a rule of thumb, for every 10 PSIG of compressed air generation increase the energy costs increase 5-7.5%

By developing a total understanding of the compressed air system, including the use of tools such as the Pressure Profile, steps to best maximize the performance while reducing costs can be performed.

If you have questions about getting the most from your compressed air system, 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.

Brian Bergmann
Application Engineer

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Compressed Air Filtration – Particulate, Coalescing, and Adsorption Types

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Compressed air systems will contain contaminants that can lead to issues and increased costs through contamination of product, damage to the air operated devices, and air line clogging and restriction. Proper air preparation is critical to optimizing performance throughout the plant operations.

Because there are different types of contaminants, including solid particles, liquid water, and vapors of water and oil, there are different methods of filtration, each best suited for maximum efficiency in contaminant removal.

Particulate Filters – The compressed air flows from outside to inside of the filter element. The compressed air first passes through a baffle arrangement which causes centrifugal separation of the largest particles and liquid drops (but not liquid vapors), and then the air passes through the filter element.  The filter element is usually a sintered material such as bronze.  The filter elements are inexpensive and easy to replace. Filtration down to 40-5 micron is possible.

9001
Particulate Type Filter with Sintered Bronze Element

Coalescing Filters – This type operates differently from the particulate type.  The compressed air flows from inside to outside through a coalescing media. The very fine water and oil aerosols come into contact with fibers in the filter media, and as they collect, they coalesce (combine) to form larger droplets towards the outside of the filter element. When the droplet size is enough the drops fall off and collect at the bottom of the filter housing.  The filter element is typically made up of some type glass fibers.  The coalescing filter elements are also relatively inexpensive and easy to replace. Filtration down to 0.01 micron at 99.999% efficiency is possible.

9005
Coalescing Type Filter with Borosilicate Glass Fiber Element

Adsorption Filters – In this type of filtration, activated carbon is typically used, and the finest oil vapors, hydrocarbon residues, and odors can be be removed.  The mechanism of filtration is that the molecules of the gas or liquid adhere to the surface of the activated carbon.  This is usually the final stage of filtration, and is only required for certain applications where the product would be affected such as blow molding or food processing.

When you work with us in selecting an EXAIR product, such as a Super Air Knife, Super Air Amplifier, or Vortex Tube, your application engineer can recommend the appropriate type of filtration needed to keep the EXAIR product operating at maximum efficiency with minimal disruption due to contaminant build up and unnecessary cleaning.

If you have questions regarding compressed air filtration or 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.

Brian Bergmann
Application Engineer

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Powering Cabinet Coolers with Compressed Air

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Dual CC outside
NEMA 4X Dual Cabinet Cooler

Not too long ago, I was contacted by one of our customers regarding the Cabinet Cooler Systems and the quality of the compressed air used to power them.

The specific questions were:

  1. What happens if the compressed air gets dirty with oil or other particles if sufficient filtration is not available at the facility where Cabinet Cooler is being used?
  2. Where does the oil particle go, into the cabinet or out through the hot exhaust or both?
  3. If it goes into the Cabinet Cooler, should one expect a spray or will it simply form small droplets?
  4. Is there a way to filter the cold air outlet?

Dirty, oil laden air would exhaust throughout the Cabinet cooler (both hot and cold flows) as well as into the inside of the attached cabinet if the air were contaminated and there was not any filter located up-stream of the Cabinet Cooler System. This is precisely why we always recommend the use of filter/separator and oil coalescing filters to clean up the compressed air before it goes into the Cabinet Cooler. In fact, we include a five micron, auto-drain, filter/separator with all our stock systems. If oil is a known contaminant in a customer’s system, we will also recommend use of an oil coalescing type filter which we can provide as well. Without a coalescing filter, you can expect any oil in the compressed air supply to be atomized into a vapor which then has possibility of settling on components inside the cabinet.

Filtering the compressed air while it is still in its compressed state and before it goes into the Cabinet Cooler is the only way to make sure that the air is properly cleaned before processing through the Cabinet Cooler System. Filtering the air after it has gone through the Cabinet Cooler System is not possible. Many filtration systems rely on the high velocity of the compressed air for their filtering capability. If it is no longer in its compressed state (a condition that exists at the cold outlet of the Cabinet Cooler), then the right conditions for proper treatment do not exist. Also, by the time the air exits the Cabinet Cooler, your primary need for it is going to be for cooling anyway. Attempting to add filtration to the cold air output will interfere with the cooling function, which negates the purpose for having the Cabinet Cooler.

As compressed air and the systems that produce it become more widely understood, filtering, drying and removing oil from the compressed air stream are tasks that are done on the production side of things.

The best way to proceed is to have the necessary filtration on the compressed air supply, at the point of use, even if the facility has filtered, clean, dry air. It would still be good to employ it just in case any up-stream equipment that is normally used to clean up the air, went down for some reason. I call it the belt and suspenders method. The redundancy is worth the investment.

Neal Raker, International Sales Manager
nealraker@exair.com