2350 loader creeps down

Yellott Canby · Jul 23, 2009

Hello,
I have a 2350 loader on a 1466. The loader creeps down, particularly with a heavy load in it. It is the loader itself that creeps and not the bucket tilt, and it is getting worse Is this the seals in the cylinder on the loader or the valve on the tractor? Thought I might see if the loader creeps down with the hydraulic lines off. Thought that might be a good test.
Thanks, YC

Bob · Jul 23, 2009

Yes, if you have "quick connects" and can disconnect the loader cylinder hoses from the valve (with the loader up) and it STILL leaks down, you have confirmed at least one of the piston seals has failed.

John G. Hasler · Jul 23, 2009

A cylinder under compression cannot leak down unless oil leaves the cylinder.

Bob · Jul 23, 2009

"A cylinder under compression cannot leak down unless oil leaves the cylinder. "

Whatever you say, John.

I can't begin to tell you how many instances I've seen when the piston seal fails on a double-acting cylinder and it creeps down as the oil moves past the piston.

Randy in NE · Jul 23, 2009

The oil can leak from one side of the cylinder to the other side if the seal is bad, regarless if the hose is connected to the tractor or not.

John G. Hasler · Jul 23, 2009

But when it gets to the other side it has nowhere to go but out. As the piston slides into the cylinder the shaft follows it. Thus there is less room for oil when the cylinder is retracted than when it is extended. Therefor, oil being incompressible, the cylinder cannot retract unless some oil leaves it (ever run across the instruction "Check level with all cylinders extended"?)

What does happen is that as oil leaks past the seal the pressure in the two chambers of the cylinder equalizes. The load is then being effectively supported by the cross-sectional area of the shaft rather than that of the piston. As a result the pressure goes way up, forcing oil past the check valve (which is probably as old and weak as the cylinder seal).

charles todd · Jul 23, 2009

I am an Industraial Multi-Craft Manintenance Technician. If you believe a sealed system cannot leak down, I'll sell you a bridge across to the ocean front property in Arizona.

--True, oil cannot leave the closed circuit (unless there is an external leak)
--False, a sealed cylinder, full of oil cannot leak... It will leak past the piston seals and displace its self.

CT

John G. Hasler · Jul 23, 2009

Yes, try disconnecting the hoses immediately after raising a load. If the piston seals are good the cylinder won"t move at all. If they are bad it will come down a little bit as the pressure equalizes (and therefor rises), compressing the bit of gas that is always present and stretching the hoses a bit. It can"t come down all the way without leaking a volume of oil equal to the volume of the shaft, since the shaft ends up inside the cylinder which, when the cylinder was extended, was completely full of oil.

By the way, have fun reconnecting those hoses.

Anonymous-0 · Jul 23, 2009

John Hasler is absolutely correct. Oil has to have some place to go and when rod is going into cyl, where can it go except out. If you are supporting a load with a cyl that extends , not contracts, then you have a different situation as rod is coming out of cyl so space is added to other side for oil to go.

mattofvinings · Jul 23, 2009

Just keep in mind that an extended hyd cylinder with plugged ports/hoses and a load on the rod is at static equilibrium...but the fluid pressures are not in equilibrium!

The mechanical force/load on the extended rod is creating a pressure differential across the piston seal. Higher pressure on the bottom of the piston and lower pressure on the rod side of the piston. It is an easy thing to visualize with pressure gages.

If the piston seal cannot maintain the pressure differential (IOW leakage) then the pressures will slowly equalize by virtue of the rod being forced completely into the cylinder and the piston resting on the bottom of the tube (or at any other mechanical travel limiter).

IMHO what you have described is an excellent test to isolate the spool from the piston seal.

Yellott Canby · Jul 24, 2009

Hello, Thank you all for all the advice. I figured that if one of the piston seals has failed it will leak down with the hoses off. I would rather have it be that than the tractor valve.
I figure to pick it back up with a forklift to reattach the hoses.
Thanks,
YC

2350 loader creeps down

Yellott Canby

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Bob

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John G. Hasler

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Bob

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Randy in NE

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John G. Hasler

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charles todd

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John G. Hasler

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Anonymous-0

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mattofvinings

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Yellott Canby

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