Weird FEL behavior

[ovrszd]

Lets think about this. If there are no external leaks and the valve is not leaking, it is impossible for the cylinders to compress regardless of the condition of their seals. Where would the displaced fluid go?

 

[oldnslo]

Lets think about this. If there are no external leaks and the valve is not leaking, it is impossible for the cylinders to compress regardless of the condition of their seals. Where would the displaced fluid go?

You are correct that a cylinder will not retract with bad piston seals but on a loader a 1/4 inch of cylinder movement could be 6 inches of bucket movement. 1/4 inch of cylinder movement would just be the pressure equalizing in the cylinder

Like others I suspect lift cylinder leaking internally

 

[Threepoint]

Lets think about this. If there are no external leaks and the valve is not leaking, it is impossible for the cylinders to compress regardless of the condition of their seals. Where would the displaced fluid go?

I agree with Richard. For the cylinder rods to move further into the boom lift cylinders during compression they must displace an equivalent volume of oil. Assuming no leaks at the gland seals, fittings, hoses and valve, the oil has no place to go. So even if the piston seals are badly worn, or even missing altogether, the cylinders are locked and can't compress further.

The cylinders can extend in those conditions, but extension doesn't seem consistent with the FEL behavior 83Ttype describes. :scratchchin:

 

[Threepoint]

You are correct that a cylinder will not retract with bad piston seals but on a loader a 1/4 inch of cylinder movement could be 6 inches of bucket movement. 1/4 inch of cylinder movement would just be the pressure equalizing in the cylinder

Like others I suspect lift cylinder leaking internally

Interesting point about pressure equalization! But I'm not visualizing how that could account for even 1/4" of the rod entering the cylinder if the cylinder is completely full of oil. Now, if there's even a small amount of air in the cylinder, I could see it. But the air would have to have entered somehow, so that would mean an external leak. Perhaps, e.g., past the gland seals?

 

[Leejohn]

Look at the picture and you can see the load check valves. Some control valves have them on the bottom. Easy to check and fix, just make sure all pressure is off of system. Read how they work in that picture.

 

[ovrszd]

Leejohn, very good file. I saved that one. Makes sense even to a monkey like me!!

 

[83Ttype]

You are correct that a cylinder will not retract with bad piston seals but on a loader a 1/4 inch of cylinder movement could be 6 inches of bucket movement. 1/4 inch of cylinder movement would just be the pressure equalizing in the cylinder

Like others I suspect lift cylinder leaking internally

This makes the most sense to me. I couldn't mentally picture how it would be leaking, but still hold a load. The 1 good cylinder is doing all of the work (and holding) and the pressure bypasses in the bad cylinder and equalizes in both. I can at least kind of picture it now. There are no external leaks at all on the tractor, just FYI.

I did a quick test to see how long the loader holds up with no load on it. It drops 4 inches every 10 minutes, 2 ft per hour.

I'll pull one of the cylinders and do some testing. Rebuild kits are only about $50 / side so even just rebuilding both of them wouldn't cost a fortune.

What about disconnecting one of the cylinders at a time and capping the lines so the other cylinder does all the work. The "bad" cylinder should show the symptoms and the "good" one should be completely normal.

Thoughts?

 

[oldnslo]

Look at the picture and you can see the load check valves. Some control valves have them on the bottom. Easy to check and fix, just make sure all pressure is off of system. Read how they work in that picture.

Lee,
Valid concern when the spool is shifted but not valid when the spool is in the center or home position since the spool now blocks flow to load checks.

 

[oldnslo]

This makes the most sense to me. I couldn't mentally picture how it would be leaking, but still hold a load. The 1 good cylinder is doing all of the work (and holding) and the pressure bypasses in the bad cylinder and equalizes in both. I can at least kind of picture it now. There are no external leaks at all on the tractor, just FYI.

I did a quick test to see how long the loader holds up with no load on it. It drops 4 inches every 10 minutes, 2 ft per hour.

I'll pull one of the cylinders and do some testing. Rebuild kits are only about $50 / side so even just rebuilding both of them wouldn't cost a fortune.

What about disconnecting one of the cylinders at a time and capping the lines so the other cylinder does all the work. The "bad" cylinder should show the symptoms and the "good" one should be completely normal.

Thoughts?

since the cylinders are mechanically tied together you would have to either remove one of the clevis pins & cap the lines or figure out some way of catching the oil being expelled from the disconnected cylinder since you can not just plug those ports.

 

[ovrszd]

since the cylinders are mechanically tied together you would have to either remove one of the clevis pins & cap the lines or figure out some way of catching the oil being expelled from the disconnected cylinder since you can not just plug those ports.

The rate of drop he described cannot be pressure equalizing in the cylinders. The valve has to be leaking internally if there are no external leaks, which he said there are not.