The Case For Desiccant Compressed Air Dryers

Most people are familiar with desiccant from the small packets we find enclosed with a new pair of shoes, in a bag of beef jerky, or in some medication bottles.  These packets almost always say “Do Not Eat,” and I get that for the ones in the beef jerky or the pill bottles, but I just don’t understand why they put it on the desiccant packets bound for a shoe box…

Anyway, desiccant (in MUCH larger volumes than the household examples above) are also used to get water vapor out of compressed air.  Desiccant dryers are popular because they’re effective and reliable.  The most common design consists of two vertical tanks, or towers, filled with desiccant media – usually activated alumina or silica gel.

These materials are prone to adsorption (similar to absorption, only it’s a physical process instead of a chemical one) which means they’re good at trapping, and holding, water.  In operation, one of these towers has air coming in it straight from the compressor (after it’s become pressurized, remember, it still has just as much water vapor in it as it did when it was drawn in…up to 5% of the total gas volume.)

When that tower’s desiccant has adsorbed water vapor for long enough (it’s usually controlled by a timer,) the dryer controls will port the air through the other tower, and commence a restoration cycle on the first tower.  So, one is always working, and the other is always getting ready for work.

There are three methods by which the desiccant media can be restored:

  • Regenerative Desiccant Dryers send a purge flow of dry air (fresh from the operating tower’s discharge) through the off-line tower’s desiccant bed.  This dry air flow reverses the adsorption process, and carries the water away as it’s exhausted from the dryer.  This is simple and effective, but it DOES use a certain amount of your compressed air.
  • Heat Of Compression Desiccant Dryers use the heat from pressurized air straight from the compressor(s).  This hot air is directed through one tower, where it removes moisture from the desiccant.  It then flows through a heat exchanger where it’s cooled, condensing the moisture, before it flows through the other tower to remove any remaining moisture.  This method doesn’t add to your compressed air usage, but it only works with oil-free compressors.
  • The third method uses a hot air blower to flow heated air through the off-line desiccant bed.  It’s similar to the Regenerative type, but it doesn’t use compressed air.  However, they DO require a certain amount of wattage for the heater…remember, electricity isn’t cheap either.

As an EXAIR Application Engineer, it’s my job to help you get the most out of our products, and your compressed air system.  If you have questions about compressed air, call me.

Russ Bowman
Application Engineer
EXAIR Corporation
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Multi-tools, Adjustable Wrenches, and Vortex Tubes

I like tools and gadgets that can perform a variety of functions. From the Swiss Army Knife, to the multi-tools by Leatherman, Gerber, etc., I’m a sucker for anything that might offer me the chance to NOT dig through my toolbox for something that’s probably not there because it didn’t get put back the last time.

That’s why another of my favorite tools is the adjustable spanner…you may know it as the Crescent, or perhaps, the “all sixteenths,” wrench. Its popularity is cemented in American legend, as pioneering aviators Charles Lindbergh and Richard Byrd both famously included them in the scant provisions they took with them on their long flights across the Atlantic and to the North Pole, respectively. Remember, this was back when every single ounce of weight that someone took on a plane with them had to be carefully considered. Which, come to think of it, isn’t that much different than commercial flight luggage constraints today. But I digress.

Lindbergh took only "gasoline, sandwiches, a bottle of water, and a Crescent wrench and pliers" on his famous flight.
Lindbergh took only “gasoline, sandwiches, a bottle of water, and a Crescent wrench and pliers” on his famous flight.

One other thing this tool is sometimes called is the “Crescent hammer.” Dear reader, don’t do that to such a fine instrument. Seriously; go back to the toolbox that it came from…odds are, you’ve got a real hammer there. It will strike the handle end of the screwdriver that you intend to use as a chisel much squarer. While you’re there, get your safety glasses too. You’re welcome.

Now, it’s not always a problem to use things for applications other than what they were intended for…not always. In fact, I had the pleasure of helping someone do just that with a Vortex Tube recently. During the assembly of the electrical connectors they make, they put a small dab of sealant inside. When wire is inserted by the user, this sealant helps hold it in place, and protects the bare end from corrosion. They were, however, putting more than they needed into the connectors, and were looking for a way to quickly heat the piece, which would thin out the sealant and produce an even coating inside, allowing the rest to be recovered and reused.

They were already familiar with EXAIR products, since they’re a big user of our Safety Air Guns. The caller had found our Vortex Tubes in his copy of our catalog, and was wondering if he could use the hot air flow for this. He knew what temperature he needed to reach, but didn’t have a feel for how much (or little) air flow would be needed to do the job. This was no problem, since our Model 3930 Cooling Kit comes with a Medium Vortex Tube and ten different Generators, which allows for a range of hot flows from 2 to 32 SCFM (56 to 906 SLPM), and temperatures from 96° to 261°F (35° to 127°C).

3930

If you’ve got an application that you want to use a Vortex Tube for – be it cold or hot air that you’re after – give us a call. Oh, and I was just kidding about the screwdriver; I know you have a chisel, and, like mine, it’s somewhere. Somewhere…

Russ Bowman
Application Engineer
EXAIR Corporation
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