To replace #3545 Twin dryer. ~~~~~ To follow up.     3545 air dryer replaced. Security/function check - OK. #3545 Air Dryer S/N : OLD : 01512591 NEW : 3517220346  Chan SW/Hanafi 44162 3545 - Found safety valve continuously air discharge.  3545 found air compressor safety v/v discharging at 7 bar. Swapped safety v/v from #3545 to #3546 but fault remained. Further checked air compressor output free from choke. Checked air dryer for purging & found air dryer unable to purge. Further found safety v/v blowing on changeover of dryer. OPS 20 raised for air dryer c/o.  Kana 44161