Tag: stp

What’s So Great About EXAIR’s CAD Library?

Published on by Russ BowmanLeave a comment

I was first introduced to CAD drawings when I was in the Navy. Right out of Nuclear Power School, I reported to a new construction Trident submarine. My first job was taking paper P&ID’s (Piping & Instrumentation Diagrams) to the Engineering room to verify that the valves, flanges, welds, pressure gauges, thermometers, etc. of various reactor and steam plant piping systems were in the right place, correctly labeled or marked, and visually free of defects. They’ve come a LONG way, technologically, since then:

When I left the Navy, I included some vague verbiage about CAD expertise on my resume. That actually got me a pretty cool job with an industrial pump company…making to-scale drawings of pump and drive assemblies, usually mounted on steel baseplates, that showed distances from the pump’s fluid ports to the baseplate mounting holes, so the millwrights & pipe fitters could work together to prepare for installation.

The absolute number one most important resource I had at my disposal was the ability to get to-scale CAD files (.dxf or .dwg) from pump, motor, gearbox, coupling, etc., manufacturers. The first rule of CAD is “never draw anything twice” and I rarely had to draw anything, except for items that we were fabricating ourselves. I had to call some manufacturers; others I could email; some would mail out a 3.5″ floppy disk (I know I’m dating myself with that one) or a CD (before THEY went obsolete) with everything they made on it…and some had drawing files you could download straight from their website. Just like EXAIR does.

Almost all the drawings I made back in the late 20th Century were 2D (front and side views), but nowadays, almost everyone uses solid modeling software (or apps) for drawings. This has the distinct advantage of being able to see the assembly from any angle, so you can tell right away if there’s going to be physical interference between two parts in close proximity to each other. While you can download models in a number of formats from the EXAIR website, .stp files are common to most modeling apps, so they’re the ones that get downloaded most.

If you have questions about EXAIR products — how they work, what they’re made of, which one is best for your application – give me a call. And if you need a drawing, I can help with that too.

Russ Bowman, CCASS

Application Engineer
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Standard Temperature and Pressure: What is STP?

Published on by John BallLeave a comment

When it comes to volumetric flow rates, you probably noticed the prefix of an “S” for SCFM and SLPM, or an “N” for NM3/hr.  The “S” prefix is for Standard conditions, and the “N” prefix is for Normal conditions.  For practical reasons, they are the same thing.  What does this mean? 

Let’s look at the Ideal Gas Law in Equation 1:

Equation 1:

PV = nRT 

P – Pressure

V – Volume

n – No. of moles

R – Ideal Gas constant

T – temperature

Since air is compressible, it will react in different ways.  If we keep the volume the same and lower the temperature, the gas pressure will go down.  If we keep the temperature the same and decrease the volume, the gas pressure will go up.  If we go to a higher elevation, the number of moles is reduced, which will lower the gas pressure.  With the different degrees of changes, it is difficult to compare.  So, organizations decided to place a standard on these conditions to help compare results.  The definition is referred to as STP, or Standard Temperature and Pressure. 

In most cases, the Standard Temperature and Pressure is set at 20oC and 1 atm (1.013 bar).  If we transition all pneumatic units to this condition, we can then compare the results for each product.  We can determine which units actually use less compressed air or have higher forces.  Or if we decide to use a different STP, we can do that as well as long as we use the same temperature and pressure. 

I like to 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, more pressure is applied to the balloon, and the volume will decrease.  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 to the surface, the balloon will expand back to the original size.  When doing comparisons, we need to be in the same condition, or for the balloon example, it will look like the balloon will need less air at lower depths than at the surface.   

The reason for this explanation is that some competitors like to use lower pressures to rate their products.  As an example, Competitor A rates their nozzles at 5 bar (72.5 psig).  EXAIR uses 5.5 bar (80 psig) for most of our products.  By comparison, we cannot say if one unit uses more or less compressed air unless we set them at the same conditions.  The best place to compare is at a Standard Temperature and Pressure, or STP.   I go into more detail in my blog about air flows with “CFM, ICFM, ACFM, SCFM: Volumetric Flow Rates Explained”.  EXAIR offers Super Air Knives, Super Air Nozzles, and Super Air Amplifiers to efficiently blow compressed air.  So, when a company states a compressed air flow, verify the pressure and temperature at which they recorded that information.  It will help you to be more in tune with what you are getting (allow for an apples to apples comparison). If you need any help in doing comparisons, an Application Engineer at EXAIR will be happy to assist you. 

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo:  balloon helium air flying bright by stux.  Pixabay license

Utilizing CAD Files

Published on by Russ BowmanLeave a comment

When I was in 6th grade, our art teacher, Mrs. C, taught us to draw fruit one day. I was academically gifted (I’d had straight A’s since 1st grade) but I was AWFUL at drawing. I was doing OK with my orange, apple, and even my banana. When it came time to draw a pear, I realized I had 35 cents in my pocket (that’s what milk for snack time cost) so I pulled out that quarter & dime, used them to trace a quarter-sized circle with a dime-size circle slightly intersecting it, erased the middle parts, and “free-handed” little arcs to complete the pear shape. Mrs. C told me I wasn’t allowed to do that and gave me my first bad grade – ever. Now, I LOVE going to art museums and taking in the wonders of those who are far more skilled than I with pen and brush, but I STILL have no aptitude or desire for drawing anything myself….with a pen or brush, that is.

My first job out of the Navy involved some very basic CAD use…mainly making simple changes or additions (and usually just title block text) of existing drawings. As I more familiar with CAD, I realized the method for drawing a pear shape in CAD was, in fact, my own personal grade school method: intersect two circles, trim, and fillet. So there, Mrs. C!

My next job took my CAD utilization a bit further…making assembly drawings of systems, using existing CAD files for the individual components that made up the system. The key word there was “existing” – the First Law of CAD is, “Don’t ever draw anything twice.” So, I’d get CAD files from the manufacturers, insert them into my template, put them where I wanted them to be in relation to the other pieces of my little puzzle, send the drawing(s) to the end user for piping and foundation prep, and as long as the folks in the shop followed my drawings (which is was hard not to), everything worked out great.

Now, this was way back in the 1990’s, so I got most of my CAD files via email, and, occasionally, on 3.5″ floppy disks or CD’s. EXAIR Corporation has offered drawing files for our products in our CAD Library for many years now. You can always find four fundamental file extensions:

  • PDF – these can be opened with Adobe Acrobat…they’re “just for looking at”. They don’t denote any particular scale, and won’t directly import to a CAD file. They’re useful for quick & easy answers about overall dimensions, bolt hole sizes, thread pitches, etc.
  • DWG – this is AutoCAD’s “native language.” These files will open seamlessly in AutoCAD, if that’s what you’re using, along with many other programs. But, if it doesn’t.
  • STP – we’re well in to the 21st Century, and many designers have moved on from the above mentioned 2D files to solid models. Most solid modeling programs are compatible with these files.
  • SAT – these are, to STP, what DXF is to DWG…a “more friendly” file for certain solid model programs.

With the launch of our new website, we now offer 64 native extensions so you (hopefully) do not have to modify, import, or convert any drawing that would take additional modification – just download the file you need right from our Resources, 3D Models and CAD drawings link. And dare I say, if you can’t find the extension you need, you are using some fairly obscure software – perhaps an SAT or STP file will suit you.

If you’re designing a system or making an assembly drawing incorporating EXAIR catalog products, we have all of these in the CAD Library. If you need one for something that’s not in the catalog – a Super Air Knife less than 60″ long with a Plumbing Kit installed, for example – we can provide that as well...just contact an Application Engineer.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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