During a routine check of the Y-end purge-air supply today, I found that the drying tower had a "switching error" with the Left tower regenerating and the Right tower drying.  I reset this and confirmed that both towers were switching normally.  Hmmm..  Chandra also had this happen in the past but the issue seems to be intermittent - with long periods of no errors detected.  For now I will try and check this on a daily basis as opposed to every few days.  

Also, the current demand for purge-air from the VE is resulting in an output pressure of 0.8 psig.  Even so, the skid is alternating between 3 - 4 compressors.  I'll try and revisit if the programmed pressure set points at which the PLC adds addition compressors is easily changed.  If so, I would like to see fewer compressors running for this, relatively modest, demand.