I am having problems with a grasso RC311 compressor. I think the High pressure head should load as soon as there is oil pressure, with this compressor there is a long delay. I have fitted a pressure gauge to the line feeding the loading piston and get no pressure untill it loads then I get over 200 psi and every thing works ok. I have stripped and checked all the oil pump including the control pistons. There is oil pressure at start up imediately for the crank shaft (2.5 bar) so I can,t figure out why I can,t get pressure for the loading gear? Any body got any ideas?