The Importance Of Properly Sized Compressed Air Supply Lines

EXAIR Corporation manufactures a variety of engineered compressed air products that have been solving myriad applications in industry for almost 37 years now.  In order for them to function properly, though, they have to be supplied with enough compressed air flow, which means the compressed air supply lines have to be adequately sized.

A 20 foot length of 1/4″ pipe can handle a maximum flow capacity of 18 SCFM, so it’s good for a Model 1100 Super Air Nozzle (uses 14 SCFM @80psig) or a Model 110006 6″ Super Air Knife (uses 17.4 SCFM @80psig,) but it’s going to starve anything requiring much more air than those products.  Since compressed air consumption of devices like EXAIR Intelligent Compressed Air Products is directly proportional to inlet pressure, we can use the flow capacity of the pipe, the upstream air pressure, and the known consumption of the EXAIR product to calculate the inlet pressure of a starved product.  This will give us an idea of its performance as well.

Let’s use a 12″ Super Air Knife, with the 20 foot length of 1/4″ pipe as an example.  The ratio formula is:

(P2 ÷ P1) C1 = C2, where:

P2 – absolute pressure we’re solving for*

P1 – absolute pressure for our published compressed air consumption, or C1*

C1 – known value of compressed air consumption at supply pressure P1

C2 – compressed air consumption at supply pressure P2

*gauge pressure plus 14.7psi atmospheric pressure

This is the typical formula we use, since we’re normally solving for compressed air consumption at a certain supply pressure, but, rearranged to solve for inlet pressure assuming the consumption will be the capacity of the supply line in question:

(C2 P1) ÷ C1 = P2

[18 SCFM X (80psig + 14.7psia)] ÷ 34.8 SCFM = 49psia – 14.7psia = 34.3psig inlet pressure to the 12″ Super Air Knife.

From the Super Air Knife performance chart…

This table is found on page 22 of EXAIR Catalog #32.

…we can extrapolate that the performance of a 12″ Super Air Knife, supplied with a 20 foot length of 1/4″ pipe, will perform just under the parameters of one supplied at 40psig:

  • Air velocity less than 7,000 fpm, as compared to 11,800 fpm*
  • Force @6″ from target of 13.2oz total, instead of 30oz*
  • *Performance values for a 12″ length supplied with an adequately sized supply line, allowing for 80psig at the inlet to the Air Knife.

Qualitatively speaking, if you hold your hand in front of an adequately supplied Super Air Knife, it’ll feel an awful lot like sticking your hand out the window of a moving car at 50 miles an hour.  If it’s being supplied with the 20 foot length of 1/4″ pipe, though, it’s going to feel more like a desk fan on high speed.

The type of supply line is important too.  A 1/4″ pipe has an ID of about 3/8″ (0.363″, to be exact) but a 1/4″ hose has an ID of only…you guessed it…1/4″.  Let’s say you have 20 feet of 1/4″ hose instead, which will handle only 7 SCFM of compressed air flow capacity:

[7 SCFM X (80psig + 14.7psia)] ÷ 34.8 SCFM = 19psia – 14.7psia = 4.3psig inlet pressure to the 12″ Super Air Knife.

Our Super Air Knife performance chart doesn’t go that low, but, qualitatively, that’s going to generate a light breeze coming out of the Super Air Knife.  This is why, for good performance, it’s important to follow the recommendations in the Installation Guide:

This table comes directly from the Installation & Operation Instructions for the Super Air Knife.
All Installation Guides for EXAIR Intelligent Compressed Air Products contain recommended air supply line sizes for this very reason.  If you have any questions, though, about proper compressed air supply, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Understanding Compressed Air Supply Piping

An important component of your compressed air system is the supply piping. The piping will be the middle man that connects your entire facility to the compressor. Before installing pipe, it is important to consider how the compressed air will be consumed at the point of use.  You’ll also need to consider the types of fittings you’ll use, the size of the distribution piping, and whether you plan to add additional equipment in the next few years. If so, it is important that the system is designed to accommodate any potential expansion. This also helps to compensate for potential scale build-up (depending on the material of construction) that will restrict airflow through the pipe.

Air Compressor
Air Compressor and Storage Tanks

The first thing you’ll need to do is determine your air compressor’s maximum CFM and the necessary operating pressure for your point of use products. Keep in mind, operating at a lower pressure can dramatically reduce overall operating costs. Depending on a variety of factors (elevation, temperature, relative humidity) this can be different than what is listed on directly on the compressor. (For a discussion of how this impacts the capacity of your compressor, check out one of our previous blogs – Intelligent Compressed Air: SCFM, ACFM, ICFM, CFM – What do these terms mean?)

Once you’ve determined your compressor’s maximum CFM, draw a schematic of the necessary piping and list out the length of each straight pipe run. Determine the total length of pipe needed for the system. Using a graph or chart, such as this one from Engineering Toolbox. Locate your compressor’s capacity on the y-axis and the required operating pressure along the x-axis. The point at which these values meet will be the recommended MINIMUM pipe size. If you plan on future expansion, now is a good time to move up to the next pipe size to avoid any potential headache.

After determining the appropriate pipe size, you’ll need to consider how everything will begin to fit together. According to the Best Practices for Compressed Air Systems from the Compressed Air Challenge, the air should enter the compressed air header at a 45° angle, in the direction of flow and always through wide-radius elbows. A sharp angle anywhere in the piping system will result in an unnecessary pressure drop. When the air must make a sharp turn, it is forced to slow down. This causes turbulence within the pipe as the air slams into the insides of the pipe and wastes energy. A 90° bend can cause as much as 3-5 psi of pressure loss. Replacing 90° bends with 45° bends instead eliminates unnecessary pressure loss across the system.

Pressure drop through the pipe is caused by the friction of the air mass making contact with the inside walls of the pipe. This is a function of the volume of flow through the pipe. Larger diameter pipes will result in a lower pressure drop, and vice versa for smaller diameter pipes. The chart below from the Compressed Air and Gas Institute Handbook provides the pressure drop that can be expected at varying CFM for 2”, 3”, and 4” ID pipe.

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Air Pressure Drop

To discuss your application and how an EXAIR Intelligent Compressed Air Product can help your process, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer
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Images Courtesy of  the Compressed Air Challenge and thomasjackson1345 Creative Commons.

Super Air Knife Plumbing Kits Ensure Proper and Optimum Operation

The EXAIR Super Air Knife is a Highly Engineered and intelligently designed point of use compressed air powered device that delivers a 40:1 air amplification ratio!  This simply means that for every one part compressed air supplied to an EXAIR Super Air Knife it will entrain 40 parts ambient air into the exiting compressed air stream.  Almost as good as “money for nothing”!  Also the EXAIR Super Air Knife is designed to provide an even or “laminar” flow of air.  This is due to it being an intelligent, highly engineered compressed air product.

However if an EXAIR Super Air Knife is not connected to the compressed air supply with the appropriate number of inlet ports being fed, poor and/or erratic performance is likely.  This would manifest itself as uneven air flow and lower performance from the air knife.  In order to make this plumbing easier we offer optional plumbing kits for all Super Air Knives starting with the 24″ length all the way up to the 108″!  The 24″ and longer Super Air Knive’s require that compressed air must be supplied to multiple air inlets along its length for optimal performance.  This will ensure that the air flow is laminar and the force is even across the entire length of the Super Air Knife.  All our products are shipped with an installation guide referencing the proper recommended pipe sizes for various lengths of supply pipe.

The Plumbing Kits for Aluminum Super Air Knives provide properly sized Nitrile/PVC Hoses, Brass Fittings and a Pressure Gauge which monitors the inlet pressure to the air knife.  If the gauge shows a pressure drop when the Super Air Knife is turned on this indicates that there is an air starvation issue.  For the 303SS, 316SS and PVDF Air Knives the Plumbing Kits contain 5/8 OD SS tubing X .034 wall thickness tubing and SS fittings.

AirKnifePlumbing

So when ordering your next Super Air Knife be sure to designate the Plumbing Kit to ease your installation and to ensure top performance.

When you are looking for expert advice on safe, quiet and efficient point of use compressed air products give us a call.   We would enjoy hearing from you!

Steve Harrison
Application Engineer
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Lower Operating Costs by Minimizing Compressed Air Leaks

Almost every industry uses compressed air in some capacity. It is often referred to as the “fourth utility” In an industrial setting, next to water, gas and electric. and in many cases, is the largest energy user in the plant. With an average cost of $ 0.25 per every 1000 Standard Cubic Feet used, compressed air can be expensive to produce so it is very important to use this utility as efficiently as possible. When evaluating the performance of a compressed air system, it’s important to look at the system as a whole.

When you operate point-of-use devices at a higher pressure than necessary to perform a certain job or function, you are creating “artificial demand”. This results in excess air volume being consumed, increasing the amount of energy being lost to waste. For example, plant personnel or operators increase the supply pressure in an effort to improve the end use devices performance. When there is a leak in the system, the line pressure will actually begin to drop and performance begins to deteriorate in other areas in the plant. This not only puts stress on the existing compressor but it also leads to the false idea that a larger or secondary compressor is needed.

Here’s a quick reference on how operating pressure can directly affect operating cost:


Our Model # 1101 Super Air Nozzle requires 14 SCFM @ 80 PSIG. Based on the average operating cost of $ 0.25 per 1000 SCF used, it would cost $ 0.21 per hour to operate this nozzle. (14 SCFM x $ 0.25 x 60 minutes / 1000 SCF = $ 0.21)

If you were able to use the same Model # 1101 Super Air Nozzle operating at only 40 PSIG, while still achieving the desired end result, the air demand would decrease to only 8.1 SCFM, reducing the hourly cost to $ 0.12.  (8.1 SCFM x $ 0.25 x 60 minute / 1000 SCF = $ 0.12)

Don’t waste your money

Leaks in a compressed air system can account for up to 30% of the total operational cost of the compressor, wasting thousands of dollars of electricity per year. Some of the more common places for a leak to occur would be at connection points such as valves, unions, couplings, fittings, etc.

In this table, you will see that a certain amount of air volume is lost through an orifice or opening. If you have several leaks throughout your facility, it isn’t gong to take long for the waste and high operating costs to quickly add up as well as potential increases in repair or maintenance costs for the existing compressor. The industry average shows that any leakage more than 10%, shows there are areas where operational improvements could be made in a compressed air system.

Stay tuned to our blog over the next few weeks as we will discuss how following a few simple steps can help optimize your current compressed air system, in many cases, reducing energy costs related to compressed air waste, leading to a more economical operation.

In the meantime, if you have any questions or would like to discuss a particular application or EXAIR product, give me a call at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN