The compressor will not unload or idle. The pressure builds up until the safety valve operates - I have removed and checked the safety valve which is tight until about 7.5 Bar when it opens. Obviously somwhere in the system a device must unload the compressor so that it just idles. Has anybody any ideas ?

Many thanks

Graham, June 2010

the saftey valve is a last resort for the air system,
there should be another valve on or very near to the compressor which is tubular in shape with a plastic cover on the top this is the govenor valve which tells the compressor when to stop building the air up and when to begin building the air again these valves are prone to failure when the get clogged with soot from the air system
hope this helps

daffy4, July 2010