this valve should be your unloader valve which regulates the air pressure, sometimes this valve if its a clayton valve it will have in & out on it. the one from the chassis goes to "in" and the one from the com/ps goes to "out." if its not marked just connect any way, start engine and see if your gauges go up to, if they go over 10 bar plus on your gauges, or your emergency valve starts blowing off, change them over. when your air pressure is up to 9-10 bar it should blow air in to the comp/r to over ride the system and rugulate etc . hope this helps
austin wilkinson, November 2010
