Hydraulic Rupture #2

[hiprollc]

Hydraulic hoses should fail before the metal hydraulic lines. If the metal one failed, it was either defective, or the wrong line.

Not to hijack this thread, but it could be an inferior design. My Kubota L3700SU with only 130 hours on the clock blew a steel line last week. Thinking I had overstressed the line by backdragging and hitting a buried rock, I ordered a replacement line without asking if others had experienced similar failures and without discussing with my dealer. However, after the replacement line failed after only a few hours, I believe the lines are not up to solid hydraulic design specs. The failed line is the #4 tube, top of the four under the FEL cross brace cover. Upon closer examination and measuring, this 14 mm od tube wall thickness is only 1 mm (0.040 or forty thousandths of an inch). If you look that line size up in any hydraulic engineering data table, it is only rated at 2200 psi or so (with 4 to 1 safety ratio compared to the recommended 6 to 1). I carried the line to a local hydraulic specialist and he recommended this line/tube should only be used at less than 1500 psi. I have spoken with Kubota but they aren't too concerned and have not offered a reason for the failure or a replacement tube. The good news is that I can have this line custom made locally for under a hundred bucks with twice the pressure rating, so that's what I'll do. Probably will be my last orange tractor because of this cheap design. Makes me wonder what other short cuts and design defects are going to appear once I get a few more hours on it.

 

[hiprollc]

Forgot to upload an image of the tube failure, so here it is. The second tube failure was almost identical, just a few inches to the right.

 

[Tx Jim]

Have you checked hyd relief valve pressure setting?

 

[hiprollc]

Talked to the factory service rep and he said no adjustments for this design. I even asked about a proportioning valve between controllers - that is, I have a BH77 backhoe as well as the LA463 FEL. The backhoe is really underpowered, in my opinion, and I thought there might be a way to proportion flow and pressure between front and back. Again, factory rep says there are no adjustments.

 

[Gem99ultra]

That's a scary sight...the metal line rupturing! I'd have never guessed that could happen. I'd sure be getting the line pressure checked. I bought a simple pressure gage with a quick connect to check mine - it's set at 2300#. I read about some members bumping the pressure on theirs up, but mine's fine as it is.
Bottom line though is that "something" is definitely wrong and really needs to be uncovered before someone gets hurt.

 

[hiprollc]

Not just once, but twice on the same line (second image below)!! With no pressure settings available to change (according to the factory rep), my only option is to replace the line with one with a higher pressure rating that should handle this easily obtained pressure. Why would any manufacturer include a 2200 psi (at best) rated tube/line on a system that can routinely exceed 3,000 psi and, as some members have stated, probably close to 5,000 psi when you account for tractor work increasing the pressure above the hydraulic effort? If this was an automobile brake line, a safety recall would probably be issued by the NTSB... shouldn't there be a "National Tractor Safety Board" to protect all of us from inferior designs? Again, I have uploaded a new image below to show the second rupture.

 

[hiprollc]

As an update, I replaced the original factory line with a custom built, locally sourced hydraulic line, with all new fittings and a pressure gauge. My pressure gauge was a 0 to 5000 psi, liquid filled style, with a Maximum Pressure Indicator. On the first day of use with the new gauge, I wanted to determine how high the hydraulic pressure could be expected to rise under, what I consider, reasonable duty. While back dragging, with the bottom front lip of the bucket down and slowly pulling backwards, but not in a float mode as I was actually trying to cut into the dirt, I pegged the gauge. That means that the line in question exceeded 5,000 psi very easily. The good news is that the new line held up fine. The bad news is that I will not be back dragging like this again, although it is something that I have done with other FEL's through the years with no issues. Guess it is time to ditch the Kubota for something designed to do that kind of work.