Hello. I have a client's excavator for repair, it is 2005 Hitachi Ex225. It had a problem that appeared and diappeared, loud banging noise in hydraulic sistem under pressure and when it happened boom and arm started to shake violent, when under load. Other functions worked properly. I could not catch this problem because sometimes it happened once a weak and sometimes once a day. Then failed boom cilinder and some metal shawings got into the system and both boom spools got stuck in the control valve. With a 50/50 chance got them out, had to file edges on spools so they would move properly (i know it's a bush fix but it is what it is). So the problem now is that the banging is constant now, it starts around 300 bar pressure when boom or arm is operated, bucket, swing and trawel works properly. When it happens pressure in P2 line drops to 0 bar as I expected, and jumps back up to 340 bar in P1 pressure is pulled down to 270 bar and jumps back to 340 bar. Boom and arm don't fall when left standing in air. Instaled throttle on both pumps, pressurized up to 360 bar pump works properly (did not increase flow when presurizing). Control valve has been changed when the owner bought the excavator used. Maybe someone has some ideas or the only option is changing control valve?
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