A compressed air dryer is a device for removing water vapor from an air system.  Note my emphasis on the word vapor.  An air dryer’s main function is not removing liquid water.  That’s the role of a moisture separator and coalescing filter.

Many owners of compressed air systems overlook this distinction, and that’s not just a problem of semantics.  If you think you’ve got a dryer – but really don’t – then you’ll be frustrated and perplexed when condensation still appears at your points of use.  For whatever reason, this problem is especially common in the abrasive blasting and coatings industry.  For a number of years I’ve exhibited Blast Pak series air dryers at the annual trade show of the Society for Protective Coatings (SSPC).

I often talk to blasting and coatings contractors about how only a true dryer delivers productivity benefits: good flow of blast media, reductions of re-work and down time, and protection of nozzles.

Over the years I’ve visited with painting contractors who’ve shown me some very creative air dryers.  A while back I called on a large contractor to talk about our Blast Pak portable dryers.  He said that he already had some dryers.  He took me out into his yard and pointed to several 55 gallon drums.

Inside each drum was a large copper coil submerged in water.   The idea is that by cooling compressed air, water vapor condenses.  He’d attached a small moisture separator with a manual drain valve to the end of each coil.

I asked him, "What happens when the incoming hot compressed air heats the cooling water, and it no longer cools the compressed air and condenses out liquid?"

He said that he sends his workers out for bags of ice and dumps them into the drums.


This copper coil serves as a heat exchanger, but that does not make it a dryer. Only a dryer will prevent condensation at the point of use.

I had to give him credit for creativity.  This was one of the most clever non-air dryer dryers I’ve ever seen.  But this contractor clearly wouldn’t have won any prizes for productivity.  (For what it’s worth, he did eventually buy some Blast Pak air dryers from our local distributor.)

In the abrasive blasting and painting industry it’s also common to hear moisture separators, filters, or knock out pots referred to as air dryers.  While it is true these devices remove liquid water they are not air dryers.   Humidity passes straight through separators and filters!

Another misconception in the marketplace is that if you have an air cooled after-cooler with a separator & drain that is the same thing as a dryer.  Many new portable diesel air compressors have on-board after-coolers and filters.  After-coolers will cool the air and condense out water which is then removed by the moisture separator; however it does not take the place of a compressed air dryer.  If only a cooler is applied, some moisture will still condense in the point of use.

The Van Air Systems Blast Pak is a true compressed air drying system.  It is a portable skid mounted package consisting of an after-cooler, deliquescent dryer, and filter.  The Blast Pak cools the compressed air, separates the condensed water, and dries the compressed air to a dew point that is 10F below ambient temperature.  Drying the compressed air assures the user they will no longer condense any water out in their blast pots, nozzles, or paint guns. 

 The so-called air dryers I have discussed above will cool the compressed air and remove the condensed water but they will not dry the air.  You must add the dryer component to make sure you eliminate further condensation.  The Blast Pak is a “real” compressed air dryer.  Want to see a Blast Pak in action?  Click this link.


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