Bucket Drop

[repete]

Would require the failure of two seals ... one for each side of the loader.

I thought they were tied together hydraulically after the valve, one line out of the valve and then a tee to each cylinder. I did not realize there were independent valve outputs.

 

[KennyV]

I thought they were tied together hydraulically after the valve, one line out of the valve and then a tee to each cylinder. I did not realize there were independent valve outputs.

If one side was leaking internally it would go down SLOW as the fluid volume from Both cylinders would have to go through the one leak. KennyV

 

[repete]

If one side was leaking internally it would go down SLOW as the fluid volume from Both cylinders would have to go through the one leak. KennyV

My thought as well. It could be the cause but there is no way it would recover and function normally from that type of catastrophic cylinder failure which caused an immediate drop.

 

[Henro]

What's the chances that a cylinder seal failed and then fixed itself? I suppose that is possible...

But, I am not sure a cylinder seal failure would cause the bucket to fall anyway. The cylinder has two volumes, the piston side is larger than the rod side

If the control valve seals off each side of the cylinders, in order for the cylinder to move in the direction of the bucket falling, the excess fluid in the loader cylinders and hoses must go somewhere. and there is no where for it to go, if the control valve seals off the lines properly.

The piston side of the cylinder is on the bottom, and when the loader goes down the amount of fluid that exits from the piston side of the cylinder is greater than the amount of fluid that enters the rod side. In normal operation the difference is sent back to the hydraulic tank.

So if one cylinder failed, and became essentially the equivalent of a hose, there still would be no place for the excess fluid to go from the good cylinder, because when the rod tried to move into the good cylinder, the fluid expelled from the piston end of that good cylinder would be more than could go into the rod end, and the cylinder would lock...

My take on it anyway...

Bill

 

[Henro]

Second thought:

Even if both cylinders failed, and leaked internally, the loader would still probably not fall freely, as when the cylinder rods tried to go into the cylinders, there would be excess fluid volume generated that would have to go somewhere in order to make space for the cylinder rods.

In my mind the rapid drop must lead back to the control valve as being the cause. Either because it failed and fixed itself, or because something caught on the control lever and moved it into the lower or float position, for the time it took the bucket to drop...Lower position being more likely, as float has an indent that holds the lever in that position...

Bill

 

[Henro]

Just went out to do something with my tractor and looked at the loader lift cylinders. WHOOPS! I should never trust my memory! The rod side is on the bottom!

Everything I stated with respect to volume of fluid is correct, but we need to consider whether the reversed position of the cylinders voids the conclusion...

OK, I think the net result is the same. When the cylinder retracts, more fluid goes out one end than goes in the other. So the net affect is the same...if the fluid has no where to go, the cylinder will lock...

What do you guys think? Hydraulics is just a hobby at this end...but I am pretty sure I have a fair to good grasp of the principles...

Bill

 

[JWR]

I've got to quit walking under my loader.

You and me both !! I can think of SO MANY times I thought about the risk and went under that bucket for whatever thing of the moment. That is plain scary !

 

[JWR]

I'm going to expose my ignorance by asking a couple of questions on this one: All predicated on "Maybe the low fluid was the culprit after all..." 1) Will the hydraulic pump move air ? If YES then maybe the pump sucked some oil and then some air from the sump because the level was low. Then the cylinder fed by air and oil would go ahead and lift the bucket (being under very light load) and at that point have some oil and some compressed air in the cylinder. That leads to question 2) Is there reason why hydraulic cylinder seals might refuse fluid bypass and yet allow air to leak by ? I'm guessing YES when fluid pressure gets on the order of a few thousand psi and you never see air pressure that high and if you did it would be super hot. You can see where I'm headed ... maybe it took a little while (facilitated by very little/no load in the bucket) for a compressed air bubble highly compressed and very hot to make a path thru the oil to the seals and then "Puffffft !" ??? If it did the hot air breach of the seal would probably open a path, if only temporary, for fluid to go past the seal as well. Just a thought.

 

[JWR]

I thought they were tied together hydraulically after the valve, one line out of the valve and then a tee to each cylinder. I did not realize there were independent valve outputs.

You are correct, it is a tee after the control valve to both cylinders. There are not separate valve outlets for each cylinder.

 

[Gem99ultra]

Interesting evaluations by the above knowledgeable members... and I certainly appreciate that.

The loss of hydraulic fluid I surmised was due to a long term leak at the rear remote control valve. Nothing big and ongoing. At this point, I'm just guessing that the joystick must not have been solidly in the neutral position.

Any other thoughts are certainly welcome. But "Lesson Learned" here is that I will not under any circumstances allow myself or anyone else, under a raised bucket. What was simply a head-shaker could have easily been a fatal accident.