Hello, We have discovered an air system on our Hitachi Ex-400 and we are not sure why it is there. We began to notice hissing after we had the bucket cylinder removed, repaired, and replaced. We originally thought that it was just an air release valve releasing the air in the replaced cylinder but it seems quite substantial. Any suggestions would be great. Thanks.
Could it be the hydraulic tank with pressure bleeding off?
Some of the Japanese excavators used air in the hydraulic tank to "supercharge" the main pump inlets, keep them from cavitating. Usually there's a small air compressor on the engine with a pressure control and then a regulator to feed the tank. You should have a gauge on the panel with a green area showing 1 Kgm/3 or something like that? There's also a relief valve on the hydraulic tank to take care of overpressure. First thing to check, hydraulic tank cap is on, with the rubber gasket. Second thing to check, is relief valve blowing air? These are usually easy to spot and usually have a pull ring so you can bleed off pressure before removing the cap. Or did the Hitachis use a cap that looks like a radiator cap? I seem to remember that now. (I'm going from memories that are about thirty years old.) One thing that I always suspect when this kind of problem shows up after a repair is that the tank is over full with hydraulic oil. If there isn't enough air space above the oil, when you operate it in such a way that all the oil goes to tank, for example arm extended, bucket curled out, boom down, you get maximum oil back to tank and the air cushion isn't big enough to accommodate the change without blowing air out the relief. I won't swear to it but I think the manual says to check the oil level with the bucket curled in, arm all the way in, boom down so the bucket rests on the ground. Oil level cold mid way between the marks. Somebody feel free to correct me if that's not right. I did have a Mitsubishi 280 that the compressor governor failed on and it would blow air constantly, I think it either was a common bendix type or we replaced it with one. Cheers.
Thanks for the information. I will walk down and get a better look at it today.
The EX400-1 did come with a compressor but nothing was connected to it. The hydraulic tank is not pressurized with air.
Huh? Really? Are you saying they built the machine with a compressor that has no intended function?