The August edition of the Journal of Protective Coatings and Linings arrived recently.  I always enjoy scanning the technical articles and advertisements.  It keeps me current with the abrasive blasting and painting industry.

On page seventeen I found an article called Setting Up Air Abrasive Blast Equipment.  I’m in the compressed air treatment business so naturally I skipped ahead to the section titled “Moisture Trap.”

Unfortunately I read this brief section and groaned.  The author recommends that blasting contractors leave cracked a drain valve at the base of each moisture separator while working.  I realize that this is a common practice in the industry.  But that doesn’t make it sensible.  This practice bleeds not only liquid but compressed air.  That places an artificial load on the air compressor, which in turn burns $5 per gallon diesel fuel.  A cracked ½” ball valve easily wastes 20 CFM.  I’ll let others convert 20 CFM to GPM of wasted diesel fuel.

My bigger complaint is fundamental.  The author suggests that moisture Moisture-on-glass
separators solve the problems of wet compressed air.  Not true!  Moisture separators remove bulk liquids from compressed air lines.  But when compressed air subsequently expands within the valves of the blast machine, it cools and more liquid condenses.  This happens no matter how high the efficiency of the moisture separator, no matter how wide the drain valve is cracked.  This condensation may be a manageable nuisance to operators of small blast machines, with grit pots of 8 cubicfeet and smaller.  But introducing liquid to large multi-ton grit pots spells disaster.

The only way to guarantee liquid free compressed air both within the blast pot and at the nozzle is to use a dryer.  Unlike a moisture separator, a dryer reduces humidity in the air line.  You want to reduce humidity to keep new liquid from forming during expansion cooling.  A separator only removes liquid that’s already condensed.  A separator is useless for preventing more condensation.

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