I have a 2000 Komatsu WB140. It works well...very strong. some hydraulic cylinders will need repacking and some hoses will need to be replaced but I consider this wear and tear for the machine. It has a 24" digging bucket. I can move rocks 4 - 6 times the volume of the bucket by carefully manipulating them. Not sure how heavy but probably at least a ton or two. I can pull tree stumps similar size or larger. Overall happy and impressed with the machine. I use it quite frequently. I want it to last and avoid expensive repairs. An area of special concern is the hydraulic pump. I want to avoid cavitation or other damage. The hydraulic system has various ports to hook test gauges into. I plan to buy test gauges and test various parameters according to the service manual specs. Something that I am questioning is if the machine is not working, sitting for a while it will sometimes make a knocking noise or pulsing noise maybe about several Hertz. Sounds like fluid knocking not anything hard hitting metal to metal or gravel in the pipes...so I don't think it sounds like cavitation. rather it sounds like a spring on a relief valve bouncing open and shut repeatedly. This seems to happen when sitting at mid RPM idle, less frequently at low RPM. It is not the engine...it is either the hydraulic system, the breaking system or the transmission. I believe it is the hydraulic system. Same sound happens if I actuate a cylinder abruptly or come to a fast stop with a cylinder. The system has various pressure relief, anti cavitation valves that are limited by springs... It seems to me what is probably happening is the system is producing too much pressure/flow and dumping it back into the return line. If I actuate a cylinder while the noise is happening it goes away as if the movement of the cylinder relieves the excess pressure. The pump is an axial (piston) hydraulic pump. The swash plate is supposed to adjust hydraulicly according to power demands. It should be producing minimum flow when not in use. This issue leads me to believe the swash plate is not adjusting properly or maybe the high engine rpm is overcoming the adjustment mechanism. a simple solution is to reduce the idle RPM with the control lever when not working. Is this intermittent noise a cause of concern? I am considering installing pressure gauges in the cab so I can see in real time what the hydraulic system is doing as I work. do some machines have this? Above all I want to make sure I am not getting cavitation and damaging the pump.
You may just be hearing the return flow from your oil cooler.
That's good to hear. Are they usually that noisy? I mean I can hear it 10, 20 feet away. Granted the engine on this machine is well muffled so you can hear a lot of stuff that would probably be drowned out on a louder machine.
Don't know if it is a closed loop system but if it is could be the pump stroking and destroking due to internal leakage
Any hydraulic pump I’ve worked on with swash plates constantly are making pressure adjustments as there has to be some type of flow somewhere or it would overheat. I think you are overthinking this and looking for issues that may not be there. Personally, I only hook gauges up if I feel there is a problem. I would feel confident if the hydraulics are strong and they don’t heat up, there is not a problem. Do an oil test before anything.
Good to hear. Yeah I am probably over thinking it. The hydraulic system runs real cool. The tank only gets luke warm after hours of hard digging work. Granted the outside temperatures where I am at are in the 30s or 40s now.
When you say warm, I have always been under the belief that hydraulic systems run better at a certain temperature like 185 to 215 degrees. Too cool hydraulic systems aren’t very efficient.
Cool is efficient, it's wasted power that makes heat. The only thing I'd look into is if there is a cooler bypass and if that is working. If there is no cooler bypass, or it's not thermostatic, then it's operating as designed, and the only thing you might do is put cardboard across most of the radiator in cold conditions to warm it up faster, then remove it. For the sound, I'd check the pump drive for any sloppiness, but otherwise sounds normal. Could always post a video, but there might not be anybody that's operated a Komi backhoe to compare it to.
I would assume most or all heat generated in hydraulic systems is from friction (primarily at the pump) and a small amount from friction and cavitation flowing through the system. If you consider turbulence as incipient cavitation every system is going to have a certain small amount at valves and the pump and other areas that inevitably disrupt laminar flow. So I would agree unless I am missing something cool and strong indicates efficient operation. Cool fluid is more viscous and harder for the pump to move but I seem to be able to counteract that with more engine power. In the summer I seem to be able to get equal performance with lower rpm but it is a minor difference. So I am not worried about it. Overall very impressed with the strength and power of the machine. I have yet to meet a rock it can't move one way or another and I am in glacial till in New England. A foot below the surface there are more boulders than dirt per volume.