Many compressed air systems are designed with certain expectations about the quality of the compressed air introduced into the plant. Often, some sort of compressed air quality level is used to help guide the design the system, like those set out in Air Quality Standard ISO 8573-1. This specification guides the user as to what contaminant particle content, water vapor content and lubricant contamination is to be allowed into the system for certain quality classes that are specified by the user.
The various levels within the specification guide what type of filtration and air drying is ultimately installed in the plant. Typically, the cleaner and drier the compressed air, the more costly it is to process. But, despite good filters and air dryers, things can go wrong in your system that can cause the contamination to exceed these expectations. Just because a filter is rated for 1 micron particle size does not mean the compressed air quality is at this rating.
The photograph at right is case in point; ahead of this filter was a coalescing unit that was supposed to remove the bulk of any lubricant carry-over before it hit the final filter. Unfortunately, compressor overheating, and excessive cycling overwhelmed this filter and excess lubricant passed into it, as can be seen in the collection area under the drain, and some excess lubricant was being allowed into the air dryer beyond the filter, causing contamination issues. In addition, none of the filters had been maintained regularly, meaning the elements had lost the ability to filter to specifications, even though the pressure differential was normal. These conditions allowed lubricant to contaminate the desiccant air dryer, causing it to consume excessive purge, running up thousands of dollars a year in extra energy costs. The failure of the filtering and the air dryer causes poor air quality in the plant.
The compressed air contacts the product in a number of areas in this food products plant. The plant has a stringent cleanliness policy guiding their production machinery, but they do not test the air quality to ensure it is meeting their requirements. One wonders—with the failed filters and higher than normal water vapor content, what microbes are growing in the oxygen rich environment within their compressed air pipes?
Good design, regular maintenance and a good air quality testing program is important to ensure you are getting the air quality you paid for and expect.
By Ron Marshall
Filed Under: Pneumatic Tips