Hi, fairly new to hydraulic systems, been having some issues with a recently purchased 330 with about 10,000 hours. primary issue at the moment is the boom up control having very little modulation. all other controls are working good. If the excavator chassis is being lifted off the ground by the boom and the boom is raised to lower the excavator it is very smooth and controllable. If the boom is raised empty or with a load it is nearly impossible to raise it slowly, a couple millimeters of deflection on the joystick are the difference between stopped and full speed boom up. I have somewhat working around this by trying to always combine other movements along with boom up to steal some of the hydraulic flow. turning "boom priority mode" off does maybe help a little bit but doesn't solve the problem My plan is to test the pilot circuit pressure for boom up and see if that is where the problem lies, what other things should I be potentially looking at for this sort of issue? other adjustments or tests?
In case anyone finds this thread in the future, after studying the service manual for days I determined that it was most likely the negative flow control orifice in the valve body. Its part of a cap on the lower back portion of the valve body accessible from the bottom, there is one on the right and left end of the valve body (upper /lower pump). mine had pieces of plastic perfectly fused in to each of the holes. Create the symptoms of the valve opening but no pump pressure until near full deflection on the lever. If anyone knows where the plastic that looks like this comes from that would be good to know also!
Do you have any better photos of those pieces of plastic, maybe from after you had removed them.? They're awfully hard to identify down that dark hole.
the pieces were very small, hard to get a good photo of with the cell phone, yelow/transparent. non flexible but not super hard plastic, appear to have melted in to the holes, each piece had to be pushed back with a pick, they were not loose in there.
Kind of remind me of some of the cylinder packing or back up rings I've run across in the past. Do you have any drifting cylinders?
The thumb will drift a small amount, will come down a couple inches over the course of a half hour of digging. otherwise nothing that has been noticeable. The pump was rebuilt (engine side bearing spun in the casing causing a leak on engine side seal) about 10 hours before I bought it. The other negative flow control orifice had one peice of the plastic in it but 5/6 holes were clear. Going to pull the orifice for the straight travel soo and check that soon. Stick steals from the boom real bad even in fine control modes. going to check the solenoids for that system and then the straight travel system to see if it is causing the pumps to be always shared between stick and boom.