Water, natural gas, and electricity are, as we all know, utilities. Compressed air is also a utility and is often called the 4th utility. The quality of any utility is critical. Would you want to drink contaminated water? Use low quality natural gas that does not produce enough heat? Have continuous power interruptions from your electric company? Obviously not. We all demand high quality purchased utilities. You should expect no less of the 4thutility, compressed air, even though it’s generated on-site by your own air compressor.
When compressed air exits an air compressor it is not suitable for use in most applications. Take for example the sandblasting and painting industry. Contractors in this field rely heavily on compressed air. Hot, wet, and dirty compressed air will definitely have a negative impact on the quality of their finished product. So, what needs to be done to make sure the compressed air is made suitable for use? Here are 5 things that a blasting and painting contractor should do to obtain good quality compressed air.
1. Get rid of the heat. Compressed air discharge temperature from portable air compressors without an onboard cooler is ~100⁰ F over the ambient temperature. On an 85⁰ F summer day the discharge temperature can be as high as 185⁰ F. This is way too hot to use both from a safety and operational standpoint. A close approach after-cooler will cool the hot compressed air to within 10F of ambient temperature. Therefore, on that 85⁰ F summer day the discharge temperature from the after-cooler will be 95⁰F. The compressed air is now cooler and much safer for the contractor to use.
2. Capture the condensed water. Cooling compressed air from 185⁰ F to 95⁰ F will condense a large amount of liquid water. You need to have an efficient moisture separator will to trap the water. Even a small 185 CFM portable air compressor operating on an 85⁰ F summer day with 70% relative humidity has the potential of producing 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 thru the after-cooler. This means you need to capture 1.2 gallons of water per hour or else it will move on down the hose to your blast pot, spray nozzles, or paint gun.
Remove the condensate. All of the water and possibly some compressor lubricant carryover we trapped in our separator must be eliminated from the system. You need to use either a ball valve to manually drain the separator or a demand type drain. If the condensate is contaminated with compressor lubricant you need to dispose of it properly to comply with EPA regulations. (Equipment spotlight: The Cool Prep from Van Air Systems includes a cooler, separator, and a high efficiency oil removing filter.)
4. Reduce the Dew Point. Even though we cooled the compressed air and removed all of the condensed moisture we still have an issue to deal with. The compressed air inside the hose, blast pot, spray nozzles, and paint guns will continue to cool because the ambient temperature in our example is 85⁰ F and the compressed air temperature is 95⁰ F. As the compressed air tries to equalize with ambient temperature more moisture starts to condense out in the system. The best way to eliminate further condensation is to reduce the dew point at least 10F below ambient temperature. This can easily be accomplished with a deliquescent air dryer which reduces the dew point 20⁰ F below the entering compressed air temperature. In our example the compressed air temperature is 95⁰ F prior to going thru an air dryer. After the compressed air passes thru the deliquescent air dryer the Dew Point is 75⁰ F which is now 10⁰ F below the 85⁰ F ambient temperature. No more water can condense in your hoses, blast pots, or spray nozzles. No more clogged blast pots. No more flash rusting. No more fisheyes in your paint finish. Your 4th Utility, compressed air, is now suitable for use. (Equipment spotlight: the Blast Pak is an all-in-one portable compressed air treatment system that’s perfect for mobile blasting and coatings professionals.)
5. Watch the video on this link for additional info.