Air leaking from unloader valve when compresor pumping

Dear Mr. Cas, I have two Gentilin reciprocating piston air compressors C330/20 which are malfunctioning due to air leaking from unloader valves. Unloder valve is attached with pressure switch. During pumping air leaking and compressor running continually and trying to fill up the tanks until the cut out point (10bar) has reached. But it won't reached at cut out point because of air leaking, so it continually pumping and as the result air line and piston head are getting hot enough to burn if touched and that's why air supplying tube to the unloader valve is also ruptured. Please find the attached maintenance report for your information. Below is a link of compressor video which may also help you to figure out the problem. http://www.youtube.com/watch?feature=player_detailpage&v=tuQGGk_rTr0 Any help will be appreciated. Regards, Imran