Here is the situation. I work at a rental yard, and we have a PC-09 nicknamed "Tiny". It has bent 3 cylinders in as many months, some of the bent cylinders can be attributed to idiots using chains wrapped around the cylinder to lift things, or people hitting the bottom of the porch with the boom. But the last guy who rented it was just digging, not abusing the machine. We keep having the cylinder rebuilt and repaired, and it keeps bending. This last time it bent like a coat hanger. I suspect that way back when someone might have replaced the cylinder with a non OEM one. I can't really see anything wrong with the machine. My question is what are the possible causes of this cylinder constantly bending? Could it be some sort of problem with the hydraulic pressure to the cylinder, the cylinder is too big, too small, too long, too short? I am fairly new to troubleshooting hydraulics, but I am getting a crash course this last month with wheel motors and pumps, and "Tiny's" constant bending of cylinders. Just looking for any input anyone might have, or past experiences with micro sized excavators. My person opinion is to unload the PC-09 and buy something else because Tiny seems to be the worst possible piece of rental equipment ever.
If you've been having the same cylinder straightened repeatedly, it could be that all the bending has compromised it's yield strength. That'd explain how it could bend under normal digger conditions. Could be the relief is set to high also.
The ram was replaced not straightened to the best of my knowledge. Maybe we should have the Komatsu dealer check the relief pressure? Any chance you know where / how to adjust the relief pressure on this machine?
We have several going around and not one issue other than normal operator abuse, a few rentals and a few customer owned. Id be starting to wonder if someone has bent boom or stick. Any paint flaking?
I inspected the boom pretty closely, but I am going to check it again today for any signs of bending. Perhaps you could give me your email address and we could talk directly. I was thinking last night maybe its because the cylinder is non OEM and its too long or short, or just not the right for the application. It would be nice to have someone handy to email with a good working machine to compare things too.
This was on a small skid loader and doesn't seem likely but I'll mention it. One of the dump cylinder rods was bent or bowed about an inch. The operator stopped but I can see it turning into a pretzel if he kept going. At the bucket end of the rod, the pin and bushing in the rod and the bushing on one side of the bucket mounting were good. On the other side the bushing was mostly gone. When pressure was applied it would twist and apply a bending force to the rod. This was told me by the hydraulic repair tech. I didn't quite believe it would bend the rod like that but it's been okay ever since everything was fixed (years).
Interesting. We had someone come from the dealership and test the relief pressure, it was only 200 PSI over normal, so we ruled that out. I guess that leaves the cylinder itself, or the pins like you said. I will keep the thread updated, as we figure it out. Thanks for all your advice.
200 psi over is alot of force, if you have a 3" bore, your adding an additional 1400 lbs of load to the cylinder. Formula is area = pie x radius squared, then multiply that by 200 and that equals the force differences. The poor little machine is rated to lift 500 lbs... Another way, if its a 1" cylinder bore, and a 200psi difference, thats 629 pounds of force difference. Order a completely new cylinder from komatsu, new pins and bushings, and properly adjust relief pressure.
I agree stump, if it were a PC750, I wouldn't think much of 200 psi over spec, but on a PC-09, that's a lot. If I were constantly bending the same cylinder rod, I'd put the pressure at spec, maybe even a tad under and see where that takes me.
Sounds like good advice. Thanks for the information. 650+ pounds does seem like a lot on a 1 inch ram. The hardest part will be getting my boss to pay for the OEM cylinder because I am sure it costs a ton. A tad under spec sounds like a great plan.
When I get time to adjust pressure and replace the cylinder we will see if it bends again. We have so much to do because every machine was under water last year. We had major flooding in the area and a lot of our equipment was under water and the problems are just starting to surface. We had two wheel motors, a pump go bad last week. Anyone have any sound advice on caring for machines that were swimming in 8 feet of water for two days? lol
Ritchie Brothers
Just wanted to update the thread on our "fix". According to the Komatsu techs, these small machines do not have a relief valve on ISO side of the control selector. So when the machine is set to ISO controls instead of backhoe, there is no relief pressure. We switched the hoses around to backhoe style controls and it seems to be working properly. No way to know for sure until we let a few amateur customers rent it and try to bend the cylinder. We have our fingers crossed though. I am skeptical of the fix, but one or two of our less knowledgeable mechanics actually arrived at this conclusion so at least it's not on my resume. Seems weird that they would put the no relief pressure setup on the ISO style controls instead of the backhoe style controls that nobody likes anyway. Go figure.