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Solving Wet Air Problems to Improve Surface Preparation

MONDAY, MAY 8, 2017

By Mike Caldwell, Van Air Systems


Flash rusting, clogged nozzles, and fish eyes are common problems that can occur in the blast & paint industry due to the poor quality of compressed air — often called the fourth utility. The quality of the utilities you use is critical. Would you want to drink contaminated water? Have poor-quality natural gas that produces too little heat? Deal with continuous power interruptions? Obviously not. You demand high-quality water, gas and electricity.

Contractors who use compressed air should expect the same level of quality, even if it’s generated by their own air compressors.

When compressed air exits an air compressor it is not suitable for use in most applications. Take, for example, sandblasting and painting. Contractors in these fields rely heavily on compressed air, but when it’s hot, wet, or dirty, it will have a negative impact on the quality of the finished product. So what do blasting and painting contractors need to do to ensure the highest quality compressed air? 

1. Get rid of the heat. The compressed air discharge temperature from portable air compressors without an onboard cooler is about 100 degrees Fahrenheit (F) over the ambient temperature. On an 85 F summer day, the discharge temperature can be as high as 185° F. This is way too hot to use, both from a safety and operational standpoint. A close approach aftercooler will cool the hot compressed air to within 10 F of ambient temperature; therefore, on that 85 F summer day, the discharge temperature from the aftercooler will be 95 F. The compressed air is now cooler and much safer for the contractor to use.


Water causing problems in a compressed air line

2. Capture the condensed water. Cooling compressed air from 185 F to 95 F will condense a large amount of liquid water. An efficient moisture separator is needed to trap the water. Even a small 185 CFM portable air compressor, operating on an 85 F summer day with 70 percent relative humidity, has the potential to produce 1.8 gallons of water per hour. Approximately two thirds of the moisture vapor introduced into the system will condense out as a result of the compressed air passing through the aftercooler. This means 1.2 gallons of water need to be removed per hour or else it will move down the hose to the blast pot, spray nozzles, or paint gun.

3. Remove the condensate. All of the water and possibly some compressor lubricant carryover trapped in the separator must be eliminated from the compressed air system. Either a ball valve needs to be used to manually drain the separator or an automatic drain valve, such as Van Air Systems’ PDV, MDV or EDV. If the condensate is contaminated with compressor lubricant, it has to be disposed of properly in order to comply with EPA regulations.

4. Reduce the dewpoint. Even though the compressed air has been cooled and the condensed moisture removed, there is still a problem. The compressed air inside the hose, blast pot, spray nozzles, and paint guns will continue to cool, because the ambient temperature in the above example is 85 F and the compressed air temperature is 95 F. As the compressed air tries to equalize with the ambient temperature, more moisture will start to condense out in the system.

The best way to eliminate further condensation is to reduce the dewpoint at least 10 F below ambient temperature. This can easily be accomplished with a deliquescent compressed air dryer, which reduces the dewpoint 20 F below the entering compressed air temperature. 

In the example, the compressed air temperature is 95 F prior to going through a compressed air dryer. After the compressed air passes through the deliquescent air dryer, the dewpoint is 75 F, 10 F below the 85 F ambient temperature. No more water can condense in the hoses, blast pots, or spray nozzles. There are no more clogged blast pots, flash rusting, or fisheyes in the paint finish. The fourth utility — compressed air — is now clean, dry, and suitable for use.

ENSURING SUPERIOR SURFACE PREPARATION

Blast Pak PRO, PRO-75 from Van Air Systems

The Blast Pak PRO from Van Air Systems is a portable, single-tower deliquescent desiccant drying package, engineered specifically for use by blasting and painting contractors. The Blast Pak Pro is a solution for wet compressed air that clogs blast pots, corrodes nozzles, and causes costly rework due to excessive moisture leading to poor surface prep. This complete package is pre-assembled and welded to a forklift skid, allowing for maximum portability in mobile drying applications. With an integrated aftercooler, the Blast Pak Pro first cools hot air discharged from the compressor. Cooling forces a substantial amount of moisture to condense, but even after exiting the aftercooler, the air is still saturated with water vapor. The compressed air then passes through the drying vessel which contains Van Air Systems Dry-O-Lite desiccant. The desiccant cuts the humidity of the air roughly in half. Finally, the air flows through an after-filter to remove particulates before going downstream. The contractor is left with cool, clean and dry compressed air for superior blasting and painting quality.

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

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ABOUT THE AUTHOR
Mike Caldwell, Van Air Systems

Based in Raleigh, North Carolina, Mike Caldwell is Van Air Systems' regional sales manager. He entered the compressed air and gas industry in 1982 as an applications engineer at Zurn Industries General Air Division. Caldwell holds a BA in marketing and management from Penn State University and has completed graduate course work in industrial engineering.

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Tagged categories: Abrasive blasting; Air abrasive blast cleaning; Blasting; Surface preparation; Surface Preparation; Surface preparation equipment; Van Air Systems

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