Hydraulic Rupture #2

txdon · Mar 12, 2005

Well, I finally figured out what I did wrong to caused my steel hydraulic line to rupture, and darn, If I didn't do it again. This first picture is the way NOT to push against an unmovable object. It will put tremendous pressure on the bottom of the tilt cylinder. If you do not have the joystick moved to the left or right (tilting the bucket) which allows the pressure relief valve to operate......

txdon · Mar 12, 2005

......this might happen. The rupture occurred right near the other repaired rupture. Kubota had sent me a replacement line last month. I replaced it and was back clearing brush in an hour. I was very conscious about the relief valve operation and was constantly tilting the bucket. Four hard hours later all is well.

DUMBDOG · Mar 12, 2005

The good news is that you had not put the spare line on yet.

Have we learned out lesson yet, or just until the next time?

bugstruck · Mar 12, 2005

You're going to have to write the manual on how to find the weak spots in our hydraulic lines. I am suprised that a hose hasn't cut loose first. Is it typical for a steel line to break and a hose not to? Pic 1 shows exactly how to tax the lines, that's for sure. I guess we'll all have to start a fund to get you some remote relief valves for downstream of that joystick. Just install them uncircuited and you'll know real fast when your past the limits. /forums/images/graemlins/shocked.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif Interesting how that pressure finds the absolute weak point and exploits it with such clarity.

Junkman · Mar 12, 2005

Send this one back to them and get another free replacement.... it seems to be a safety defect that deserves a recall..... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

txdon · Mar 12, 2005

"Send this one back to them and get another free replacement" 

I can't, I feel like this was my fault.

The first time caught me off guard and I had a hard time remembering exactly what I was doing when it blew. As soon as it happened this time I noticed how hard I was pushing and what position the joy stick was in it. As I was driving back to the barn with a limp bucket I was sure hopping I blew the same line with that new spare line in the barn.
I guess next time I rupture it, I will be able to determine if it was a defective line or if repeating the same maneuver will blow any line. I will let that $30 test happen accidentally. /forums/images/graemlins/smile.gif

Scrounger · Mar 13, 2005

So what exactly happens when the line ruptures? Do you get a huge spray of fluid?

_RaT_ · Mar 13, 2005

Don, one of the first times I was using a tractor much the way you describe a fellow told me you never do that. He mentioned you will rupture a line or break something. I have a gauge on my loader that shows the pressure on my dump cylinder circuit. If I back drag, it shows very clearly that the pressures go up very fast. I can very quickly peg it at over 5000 PSI in the blink of an eye. If I were to do the opposite and go forward as you did with the momentum and/or power of the tractors drive with the bucket tilted as your first picture shows and hit either a tough object or an immovable object, I am sure I would pop my gauge and could easily see 6000, 7000, 8000 or more PSI. At some point, somethings going to give. It's better to be a hydraulic line then anything else. You are correct, it is your fault, it's learning it the hard way but your experience should help others avoid it. Is anyone listening? /forums/images/graemlins/grin.gif

Egon · Mar 13, 2005

I'm assuming it was the repaired line that failed again. The new failure looks like the repair changed the strength of the line and is a different type failure than the first. Think if that piece of line had an x-ray you'd find porosity and undercut.

Hydraulic system should be designed for any pressure the unit may be subjected to.

Egon

txdon · Mar 13, 2005

"So what exactly happens when the line ruptures?" -Scrounger


Scrounger, the line you see ruptured has a metal cover on it which is "U" shaped toward the loader. There is a muffled pop and then it looks like a garden hose of fluid being sprayed on the back of the bucket and immediately the bucket tilt goes completely limp, the bucket faces completely down and curse words fill the air, don't know where those come from. /forums/images/graemlins/grin.gif

txdon · Mar 13, 2005

Egon, That was the line that was repaired before. There could have been a negative effect from the heat of the first repair since it was so close.

 "Hydraulic system should be designed for any pressure the unit may be subjected to." 

I agree with you (that's why I conversed with Kubota on the first rupture) the hydraulic system should be designed to handle this with some relief valve in the system.

Does anyone know if it is feasible to install an in-line relief valve or warning signal - or would this cause some negative FEL operations/conditions. Of course I will check with Kubota also, if TBN can not find fault with it.

Scrounger · Mar 13, 2005

Rat could you mount a guard like that on the smaller sub-cuts like the BX? I think it would be a nice add-on for anyone who uses the bucket alot.

tractorman · Mar 13, 2005

Kubota has had a problem with weak hydraulic tubing. We have replaced half a dozen or so on late model front end loaders. Newer, heavier lines are available at your local dealer.

_RaT_ · Mar 13, 2005

"Hydraulic system should be designed for any pressure the unit may be subjected to."

You could, but you would have hoses rated at over 10,000 PSI, cylinders and their seals the same. Taking a bucket so that when the front lip hits a immovable object and is angled such that the full mass of the tractor amplifies the pressure of the fluid against the piston along with the leverage of the four bar linkage, pressures will escalate beyond what many things can handle, even industrials. The best way is simply not to be putting the loader into that configuration.

txdon · Mar 13, 2005

"The best way is simply not to be putting the loader into that configuration." - RaT 

You are right. NO Bulldozing. In fact the owners manual says:
"Do not use the bucket in the dumped position for bulldozing . As shown above this method will impose severe shock loads on the dump-linkage, the bucket cylinders, and the tractor."

I found the above quote in the area that discuss Backfilling but I proved it also is incorrect to use it tilted to push brush.

I also found on page 2, #38 "Never lift or pull any load from any point of the loader with a chain, rope, or cable. Doing so could cause a roll over or serious damage to the loader"

Does this include things we attach to our non-factory added hooks on our loaders?

Egon · Mar 13, 2005

Seems I've seen many operators on large industrial machines use the bucket like a bulldozer. This is exspecially true when cleaning parking lots with the front wheels off the ground.

My little B7100 spends much of it's time in the bulldozer mode with the front wheels off the ground.

A good design also incorporates internal PSV'S.

Egon

_RaT_ · Mar 13, 2005

I always use the bulldozer method, I just don't have it where if I catch something on the front lip like a buried boulder or stump it will leverage the bucket and create the shock load. The way you avoid it is to make sure your not in a dump configuration. To do so is asking trouble. This applies to all tractors with loaders.

WhiteRock · Mar 13, 2005

Are you thinking about putting a relief valve on for both directions of the cylinder?

Where would the PRV dump to?

What pressure would you choose?

I am not convinced this is a good idea.

_RaT_ · Mar 14, 2005

"What pressure would you choose?"

That indeed is the question. I suppose that the duration is also a consideration. After all, a 100 watt light bulb draws many thousands of amps while the filament heats up thus increasing resistance. It all takes but a fraction of a second. How much can a hydraulic line take for 1/100,000, 1/1000, or 1/10th of a second?

I don't believe it as much of an issue as one might think, but indeed, bursting a hydraulic line does happen from this very scenario. Common sense would tell me that it would be the dump circuit that would take the brunt punishment of such loader use.

PS, I see my gauge quickly peg at 5000 PSI from back dragging where no immoveable object is easily encountered resulting in the entire tractors inertia and mass forcing a hydraulic cylinder into this sceanario. I have had a few occasions where I have done what TxDon has done and felt the resulting "spring" from the pressure build up. It makes me think what the pressures could be if my gauge quickly pegs at 5000 PSI from light weight back dragging. My guess is many thousands of PSI, well in excess of 5000 PSI.

Dr_Zinj · Nov 14, 2013

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

I bulldoze and back drag with my loader.

Backdragging is usually done with the loader in float mode, so unless you have the bucket tilted down more than 45 degrees, you should just bump over any obstructions going backwards.

I use the loader in float mode when bulldozing snow. Just have to make sure the bucket is level, and I remember where all the rocks sticking up in the dirt drive are; that's not a problem as I put markers for them in before the frost.

I also bulldoze soil with the loader. The key is to go slow, plane off just an inch or so per pass, and never pop the front wheels off the ground more than a couple of inches if you hit one of those pesky boulders we grow in New Hampshire. I've been disassembling a rock "wall" the builders shoved off the side of the drive and mixed a bunch of soil with. Since it's set up over the past decade, I'll move up to the end of it and use the bucket tilt in both directions to loosen up the rocks and dirt, and then backdrag the loose stuff a bit before scooping it up. If I'm grading, then I use the backblade for the the angle and tilt to move the fill properly.