This question came from the manager of a large manufacturing plant:
Question: We have a bank of parallel refrigerated air dryers. All the air dryers are showing very good dew point, yet almost every day we have water forming in our compressed air pipes. This water causes product spoilage and is a major problem. What’s going wrong here? What should we do about this issue?
Answer: Have you measured your actual dew point with an accurate dewpoint probe? You should be aware that the dew point display on refrigerated dryers is actually the temperature of the coldest point in the dryer, not the actual dew point. If there are problems with the dryer drains or the water separator within the dryer, the water might pass through the dryer — even though the dew point reading on the dryer (actually temperature) is reading OK.
This customer actually purchased a dew point meter and found that every air dryer, except one, was producing good dew point. One dryer, an air-cooled unit (all the rest were water cooled), had been producing air with dew point readings of higher than 40° C. This was the source of the problem. This customer is located in an Asian nation close to the Equator, so ambient temperatures are really hot — not the best location for an air-cooled dryer.
It should be noted that each and every time the customer asked their air dryer supplier about the dryer display, they were told it was the actual dew point!