Hello guys, I have a question regarding a 980H. The operator claimed that while using 980H, the bucket which was loaded with dirt and elevated about 10ft off the ground, suddenly fell and slammed into the ground. He reported that the hydraulic hose had ruptured. He also stated that the back wheels of the 980H lifted off the ground when the bucket hit the ground. An engineer did an assessment and stated that the reason why the bucket fell after the hydraulic hose ruptured, was that the hydraulic circuit for the lift cylinder does not have limiting return valve on the cylinder or hose. The engineer stated that this equipment was designed like this. Is there any merit to what the engineer is saying.
He must be talking about a hold valve (several names for this). I haven't seen any wheeled or track loaders with hold valves on the cylinders. Most applications in lifting equipment (cranes, manlifts, some forklifts etc.....) will have them, especially if the machine is designed to carry personnel. Now Pettibone uses hold valves on their Carylift series but those machines are classified as material handlers.
I would be interested in knowing the serial number of this machine and the part number of the hose that failed. That being said I agree I have never seen a wheel loader that had any obvious in the system to control the downward motion of the arms or bucket. This is one of the reasons I cringe when I see a machine parked with boom/bucket in the air and even worse when someone walks under them! Now on a somewhat similar point I have seen restricting orifices in hoist cylinder lines on some haul trucks and seems some have valves in the lines that allow full flow in the raise direction but then act to restrict the oil flow in the lower direction.
As above. The machine Serial Number gets you a Hydraulic Schematic that your tame engineer can play with to his heart’s content.
Thanks for the replies.. The S/N is JMS03106.
Wheel loaders are not classified as lifting devices so a load lock is not required in that application. The odd thing for a wheel loader would be an IT machine that is used as a lifting device. Quick attach crane booms, forks and other items might have a requirement for them but I don't recall ever seeing them installed. I suppose the same could be said about telehandlers and skid steers.
Well attached is the hyd. schematic for the engineer to have fun with:
I agree with what John C said. A front-end loader is not classed as a lifting device therefore there will be no requirement for load check valves on any of the bucket lift/tilt circuits.
I would be interested to see the failed hose. To put the bucket down with a bang it must have pretty much parted in two. Rarely have I seen seen a catastrophically failed hose without there being some underlying cause, for example incorrect installation, wrong components, incorrect hose assembly etc.
I also seriously doubt that the bucket hitting the ground could have lifted the rear wheels off the deck, but that’s assuming the operator’s version of what happened is true. In fact he may have simply thought that the rear wheels had lifted.
Hose probably sat there and leaked for awhile before it let go
Either way it must have been a major hose burst to dump the oil from both lift cylinders and drop a fully loaded bucket from 10ft high down to the deck in the blink of an eye. Like KSH I'd like to know the Part Number of the hose that failed (if it's original it will have an aluminium tag on one end with the Part #) because I'm just curious to know what I/D it is. Knowing the I/D I could pretty well calculate how fast a full bucket would come down from 10ft to the ground based on the volume of oil that would be in the lift cylinders.
If you put the bucket in float, which is essentially the same, it will come down pretty bloody fast. When you're calibrating the bucket positioner and RTD you have to float the bucket from height and it's scary the first couple of times you do it. And that's with the bucket empty.
Some loaders with buckets fully curled don’t or just touch the ground ,especially with quick disconnect.
If you did hit float with a loaded bucket and it headed for the basement and you freaked and snapped it back into hold would the shock load blow the hose? Then release the boom to the ground and if the level ride was on would the accumultor have enough beans to bounce the rearend off the deck?
I could see this as a possible scenario! Especially if hose was borderline bad. I know once or twice over the years I screwed up and hit the hoist control a little too far with loaded bucket and then caught it before hitting the ground and it will raise back end up a bit! Even if bucket only dropped a couple inches before stopping it will give you whiplash!
Maybe the hose blew while lifting and in a panic the operator went to lower the boom down but accidently put it in float. I had an old skid steer that went into float a little too easily. Accidently put it float with a full bucket a couple feet off the ground. Got a small cut in my forehead from banging into the top the door opening.
The issue is that the engineer stated there should have been load locks on the wheel loader. That should be a statement on the qualifications of the engineer. The location of the accident was the Caribbean. The should be a clue as to the operational knowledge of the company using the wheel loader.
I'm thinking someone is looking to find someone with deep pockets to make a quick buck.