Tag: SCFM

A (Sample) Lexicon For Compressed Air

Published on by Brian FarnoLeave a comment

Every industry and different technical subject matter comes with it’s own lexicon of terms or vocabulary words.  More often than not, when speaking to an Application Engineer here at EXAIR you are going to hear words within our lexicon. The list I have compiled below is merely a sampling to help translate some terms that we forget not everyone knows.  Some of these are merely acronyms that get thrown around a good amount.

SCFM – Standard Cubic Feet per Minute – This is the unit we use to represent the volumetric flow rate of compressed gas that has already been corrected to standardized conditions of pressure and temperature.

PSIG – Pounds per square inch gauge – This is the unit which we use to represent the operating inlet pressure of the device.  When requesting this, we generally are looking for a pressure gauge to be installed directly on the inlet to the device with no other form of restrictions between the two.  For the most part, catalog consumption values are given in SCFM at 80 psig.  The main exception to that rule are the Vortex Tube based products.

Compressed Air – This is a utility that most industrial manufacturing facilities have available to them.   It is regular, atmospheric air which has been compressed by an air compressor to a higher pressure than atmospheric.  Generally speaking, compressed air systems will be at a range of 85-120 psig.

OSHA – Occupational Safety and Health Administration – This is the main federal agency that enforces two of the major conformance standards that EXAIR products meet or exceed.

29 CFR- 1910.95 (a) – Maximum allowable noise level exposure.  The great majority of EXAIR products meet or exceed this safety standard, our largest Super Air Nozzles
1910.242 (b) – This is the standard which states compressed air blow off devices cannot exceed 30 psig of dead end pressure.  This means, if the exit point of the air can be blocked the operating pressure must be below 30 psig.  The reason for this standard is to prevent air embolism which can be fatal.  All EXAIR products meet or exceed this standard by having multiple orifice discharge.

Coanda Effect – This is the effect that numerous EXAIR products utilize to amplify and entrain ambient air.   The Coanda effect is when a fluid jet (stream of compressed air) tends to be attracted to a nearby surface.  This principle was found by a Romanian aerodynamics pioneer, Henri Coandᾰ.  The picture below shows a Super Air Amplifier blowing a foam ball into the air and suspending it due to the Coanda effect on the surface of the ball.

A Super Air Amplifier's air stream causes a foam ball to be suspended in mid air thanks to the Coandᾰ effect.
A Super Air Amplifier’s air stream causes a foam ball to be suspended in mid air thanks to the Coandᾰ effect.

Rigid Pipe or Hard Pipe – This is the term we will often use when discussing the compressed air line that can be used to support and supply certain EXAIR products.  Generally we are referring to a Schedule 40 steel pipe, Type L copper line, stainless steel tube, or any form of pressure rated hard pipe that can be used for supplying compressed air.

Plenum – the state or a space in which a gas, usually air, is contained at a pressure greater than atmospheric pressure. Many of our products feature a plenum chamber. 

Again, this list is only a sample of the terminology you will hear us use when discussing compressed air applications.  If there are any other air/compressed air/fluid dynamic terms you may be unsure of, please contact us.

Brian Farno
Application Engineer Manager
BrianFarno@EXAIR.com
@EXAIR_BF

Deflated Footballs? What’s the Big Deal, We Talk Air Pressure Everyday

Published on by Dave WoernerLeave a comment

This week we prepare for the professional football championship game, that phrase is trademarked within the Woerner household. For a few years, we have had my friends from college over for guacamole, chicken wings, French fries, and beverages. This year our small family is now three, so we are in for a quiet evening at home. My son will most likely be asleep at kick off, but my wife and I might stay awake for the end of the first quarter. Even with the small amount of people that we will watch the game, I will still make a small spread for our family, because tradition. Tradition says, it’s Super Bowl Week – we buy avocados early in the week so they have time to ripen.

In the build up to the big game, it seems like we always get a very silly story that the media grabs a hold of and just will not let go.  I want to join them. Have you heard about the fact that the footballs that the one of teams used on offense might not have been inflated to the correct pressure. I don’t know that the fotballs were under inflated on purpose, but I also think that LaDainian Tomlinson might have been on to something, when he said “The Patriots live by the saying if you ain’t cheating, you ain’t trying.”

That was a long introduction into my blog today about pressure. The NFL Rule Book states,

“The ball shall be made up of an inflated (12 1/2 to 13 1/2 pounds) urethane bladder enclosed in a pebble grained, leather case (natural tan color) without corrugations of any kind. It shall have the form of a prolate spheroid and the size and weight shall be: long axis, 11 to 11 1/4 inches; long circumference, 28 to 28 1/2 inches; short circumference, 21 to 21 1/4 inches; weight, 14 to 15 ounces.”

From an engineering perspective this is ambiguous at best. If I read this with no knowledge of football, I would have no idea how to test whether the ball is inflated. The rule states that the ball should be an inflated urethane bladder. Then in the parenthetical phrase it lists 12 1/2 to 13 1/2 pounds. Last time I checked pounds is a measure of weight. If I received this specifications, I would put the ball on a scale to weigh it. Using some common sense a quarterback isn’t going to be able to throw a 12 pounds ball, like a bullet, 10 yards. Let alone 60 yards for that deep bomb.

If I was writing the rule book, it would read that “the ball shall be inflated to a pressure of 12 1/2 to 13 1/2 pounds per square inch gauge pressure.” With this wording there is a clear standard to be met for football to be worthy for use.

What Is Gauge Pressure?

Gauge pressure is the pressure determined by a gauge or instrument. The term is used to differentiate pressure registered by a gauge from absolute pressure. Absolute pressure is determined by adding gauge pressure to atmospheric (aka barometric) pressure. Barometric pressure can be calculated based on elevation or measured by a barometer.

What is Atmospheric Pressure?

Andrew Gatt
This bottle was sealed at 10,000 ft above sea level then moved to the beach. At the beach the bottle spontaneously crushed by the increased atmospheric pressure

 

Atmospheric pressure is the force per area that the air around us compresses our world. Above is a photo with a simple illustration of atmospheric pressure. At roughly 10,000 feet above sea level, the bottle is sealed trapping the atmospheric pressure inside the bottle. As the bottle drops in elevation, the pressure outside the bottle rises compressing bottle and the air inside.

When do I use Gauge Pressure?

Gauge pressure is used in a majority of industrial applications. For instance, EXAIR’s air nozzle performance is based on 80 Pounds per Square Inch Gauge (PSIG). No matter what elevation the air nozzles are used the flow rate and the force of the nozzle will be the same as long as the gauge at the inlet to the nozzle reads 80 PSIG.

When do I use Atmospheric Pressure?

I seldom use atmospheric pressure by itself. I often use atmospheric pressure in conjunction with gauge pressure. Meteorologists reference atmospheric pressure when referring to low pressure or high pressure weather systems.

When do I use Absolute Pressure?

In one word: calculations. Absolute pressure is equal to gauge pressure plus atmospheric pressure. In a majority of formulas or calculations, absolute pressure is used. Specifically, whenever you are using pressure to multiply, divide, or raise to a power, absolute pressure is used. There may be exceptions, but I would need to be very familiar with the formula, before I would only use gauge pressure to multiply. For instance, if you need to calculate the air usage at of an air nozzle at a different pressure (as seen in this earlier blog), you would use the absolute pressure. The flow through a nozzle is governed by Bernoulli’s principle.

Dave Woerner
Application Engineer
@EXAIR_DW
DaveWoerner@EXAIR.com

 

Photo Courtesy of Andrew Gatt. Creative Commons License

Actual vs. Standard flows

Published on by John BallLeave a comment

Have you ever noticed that when a flow rate like SCFM, SLPM, or NM3/hr is reported, there is a pressure associated with it? There is a reason for this. The “S” in SCFM and SLPM, is for Standard, and the “N” in NM3/hr is for Normal. It is the amount of air being used at atmospheric pressure and temperature. To further explain it, if you take a segment of air out of a compressed air line and place it next to you at ambient temperature and pressure, it will expand to a larger volume. Think of it like an air-filled balloon floating on top of the water. This would be the “Standard” or “Normal” condition. As you take the balloon into deeper water, the more pressure is applied to the balloon, and the volume decreases. This is because air is compressible. The balloon still has the same amount of air by weight (as the volume decreases, the density increases). If you return back to the surface, the balloon will expand back to the original size.

Pressure
Pressure

Being that the flow rate for nozzles, knives, etc., are rated at a standard or normal condition, why do we require a pressure rating? It should be at the atmospheric pressure and temperature. Well, this is where it gets tricky. Just like the air-filled balloon, the deeper you go (higher pressures), the less volume is in the balloon. So, when we have different pressures, we are trying to find the actual volume of air being used because that is what you are paying for. Also, this is where the term ACFM (lpm or M3/hr) comes into play. The “A” in ACFM is for Actual (the volume of air at the actual pressure and temperature). Pneumatic devices use this type of flow (ACFM), but for the ease of understanding, they convert it to a SCFM, SLPM, or NM^3/hr at a pressure. If we assume ambient temperatures because most of our products are used there, then the correlation between Actual and Standard is Qa = Qs * Pa/(P +Pa) .

Imperial Units                                    SI units

Qa          Actual flow (ACFM)                         Actual flow (M^3/hr)

Qs           Standard flow (SCFM)                    Normal flow (NM^3/hr)

P             Gage Pressure (psig)                      Gage Pressure (barg)

Pa           Absolute Pressure (psia)                Absolute Pressure (bara)

 

The reason for this explanation is because some competitors like to use a lower pressure to rate their products. As an example, two air nozzles are rated for 70 SCFM (119 NM^3/hr). One nozzle is cataloged at 60 psig (4.1 barg) and the other is cataloged at 80 psig (5.5 barg). By comparison, they look like they use the same amount of compressed air, but actually they do not. Under the actual condition (using the formula above), we have the following:

Imperial Units                                                                    SI Units

@60 psig                                                                              @4.1 barg

Qa = 70 SCFM * 14.7 psia/(60 psig + 14.7 psia)     Qa = 119 NM^3/hr * 1 bara/(4.1 barg + 1 bara)

= 13.8 ACFM (actual amount of air used)                 = 23.3 M^3/hr (actual amount of air used)

 

@80 psig                                                                              @5.5barg

Qa = 70 SCFM * 14.7 psia/(80 psig + 14.7 psia)     Qa = 119 NM^3/hr * 1 bara/(5.5 barg + 1 bara)

= 10.9 ACFM (actual amount of air used)                = 18.3 M^3/hr (actual amount of air used)

 

Even though it seems like they use the same amount of compressed air, you are actually using 27% more air with the nozzle reported at 60 psig than the one that was reported at 80 psig. Always remember that if you want to compare air usage, always do it at the same pressure and temperature. If you need help, you can always contact our application engineers here at EXAIR.

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

 

Image courtesy of UpUpa4me. Creative Comment License

What is the USB Data Logger for Digital Flow Meters? How Can It Help Me?

Published on by Neal RakerLeave a comment
USB Data Logger
The USB data logger works with all of EXAIR’s Digital Flow Meters and provides valuable feedback for optimizing your compressed air system.

EXAIR’s Model 9147 USB Data Logger has become one of the most valuable tools that we sell to help customers get a “view” of their compressed air usage over time. One of the important tenets we promote at EXAIR is energy savings by prudent use of compressed air through our engineered solutions (Air Knife, Air Nozzles, Air Amplifier, etc.). But how does a person in charge of such systems really “know” whether they are helping or hurting their compressed air system?

The first step is to have an appropriate flow meter which can give an indication of how much air volume is being used. EXAIR’s line of Digital Flow Meters are perfect for getting to that point with instant and direct readings that don’t need to be calculated any further. What you see on the meter is the flow in either SCFM or m3/hr calibrations.

The second step is to attach the USB Data Logger to the Digital Flow Meter so that readings can be kept over time. It is like setting up a security camera for your compressed air system. Nothing gets by without being recorded.

The USB Data Logger can be connected to just about any type of monitoring system that has a 4 – 20 mA output to which the 2-wire harness can be installed. A quick and easy initialization to choose the unit of measure, to select the frequency of measurement and some optional alarms is all that is necessary. The software package is included with the USB Data Logger and is convenient to run on a typical desktop or laptop computer. You simply, set it and forget it (at least until you want to do some reporting).

The reporting is how the USB Data Logger can help you as the person concerned with monitoring the compressed air use in your facility. Once the defined monitoring period of time has passed, the USB Data Logger can be removed from its socket, stopped from recording and the data is then downloaded into a suitable format that can be imported into EXCEL or other spreadsheet program for creating charts to analyze what is happening, when it is happening and how much compressed air is being used. In the analysis, you can compare the flow data and times with certain problems in a production line that might cause low pressure condition which shuts machinery down. You might also be able to determine where additional, point of use compressed air storage might be needed close to certain processes.

Ultimately, the USB Data Logger allows you to “see” your compressed air system in a way that allows you to sleuth out problems seen that might have no other explanation. It can also help you to justify your air savings when you apply the other air saving compressed air products that EXAIR produces by monitoring a base line for “before” performance and “after” performance. After all, it if is important to your organization, it should be measured. And compressed air is certainly a utility that should be measured.

Neal Raker, Application Engineer
 nealraker@exair.com
@exair_nr