Why you should heed warning codes

This code was warning operators of needed air dryer maintenance.

The dryer showed acceptable dew point, yet moisture problems existed.

A wire manufacturer used a refrigerated air dryer tocondition the air from its three compressors. The dew pointrequired in the plant was near 35° F, and the maintenance staffwas confident of the proper operation of the dryer, because theonboard dew point reading on the dryer control panel said thatthe reading was less than the specified level. Yet, on occasion,their production personnel complained about water in thecompressed air piping, which seemed strange — the dryerconstantly showed a good reading.

A compressed air service provider was hired as part of an energy efficiency effort. One of the auditor’s checks was to ensure that all readings were good with the compressed air dryer and that internal components were operating correctly. The auditor checked the air dryer drains; when pressing the test button, he noticed that one of the two dryer drains was passing excessive water. In fact, after 10 operations of the dryer test button, a flow of water was still flowing from the drain. Checking the actual dew point of the air at the dryer discharge with a portable meter showed that the dew point of the air was at 70° F, yet the dryer dew point display showed 34° F.

This dryer was a unit that used a cold coalescing filter to remove the water from the air stream within the dryer. A check of the manual showed a warning code “CF,” which was flashing on the dryer display panel, meant Change Filter. The dryer filter was clogged and was not properly separating the water from the airstream, allowing moisture to pass through the dryer. Plant personnel had noticed the code, but nobody bothered to look up the meaning!

It is important to realize that most refrigerated dryer dew point indicators show the temperature of the evaporator within the dryer, not the actual dew point produced. If the dryer separator or condensate drains are not doing their jobs, excessive moisture will pass undetected to downstream piping, potentially causing moisture problems. The best protection against this type of problem is good maintenance and installation of a secondary dew point probe with alarm at the discharge of the compressor room.

Ron Marshall • Contributing Editor