Conceptual Hydraulic Cylinder Question

JRaf · Jan 24, 2020

I still have some (mild) hydraulic problems on my L245DT. The 3pt hitch hydraulics are fussy. The control lever doesn’t return to the middle and if I shut the tractor off with my box scraper up, it immediately drops (slowly) to the ground. BUT if I lock the implement up by shutting down the drop speed knob, the implement will stay up (for days). Does that eliminate the piston/cylinder as the source of the problem? The piston isn’t leaking in the cylinder, right?
I’m thinking the problem lies elsewhere (probably in the Position Control Valve which I’ve rebuilt partially but not completely).

bernhardine · Jan 24, 2020

JRaf said:
.... Does that eliminate the piston/cylinder as the source of the problem?

Yesssss ....

GreensvilleJay · Jan 24, 2020

maybe....
need to know... is the cylinder a single acting or double acting ?
if single acting, then the cylinder is probably OK...but if the seal was partially bad, oil could go around/through it to the other side. The weight of the load wants to push the piston down, oil seeps past the seal
if double acting, again a bad seal would allow oil to go to the other side of the ram, down it comes....

odds however are the control valve itself has a bad oring, or 2.

If you clean/rebuild , replace ALL the orings ! Cut off the old ones to be sure you don't use an old one by mistake !!

Roadworthy · Jan 25, 2020

I may misunderstand what's going on, if so please forgive me. If the three point lift is the part in question it sounds like normal operation. My three point control has no center neutral position. There are simply varying amounts of up or down. It's a single acting hydraulic cylinder so down speed is controlled by gravity and the setting of the valve. My front loader has a center position on the control but I've not seen a three point control which did.

North Idaho Wolfman · Jan 25, 2020

JRaf said:
I still have some (mild) hydraulic problems on my L245DT. The 3pt hitch hydraulics are fussy. The control lever doesn’t return to the middle and if I shut the tractor off with my box scraper up, it immediately drops (slowly) to the ground. BUT if I lock the implement up by shutting down the drop speed knob, the implement will stay up (for days). Does that eliminate the piston/cylinder as the source of the problem? The piston isn’t leaking in the cylinder, right?
I’m thinking the problem lies elsewhere (probably in the Position Control Valve which I’ve rebuilt partially but not completely).

The position control valve on that model is proportional like Roadworthy said, so there is no center, the control lever is not supposed to return to neutral it's supposed to stop at where ever you stop at.

The only service you can do is a few O-rings in the control valve.
Sounds like you might have the feed back link set wrong.

JRaf · Jan 26, 2020

As Roadworthy said, it's the 3pt cylinder in the rockshaft housing and it's a one way system. The piston and cylinder lift and gravity does the rest.
And I agree, there's no detent, or "return to center" position on the 3pt lever. Mine seems to either want to go up or down, not find a spot where the implement just sits still (it used to work perfectly until I started to "repair" things). And as NIW suggests my problem with that might be in the feedback link.
But what I'm trying to do right now is isolate the problem. The question remains: if I lift an implement with the 3pt hitch and lock down the drop speed knob, and that implement doesn't drop down over an extended period, then the 3pt piston/cylinder system is holding pressure and working properly. Right?
I guess I'm trying to confirm that the drop speed control system works exclusively via pressure to the hydraulics, stopping or slowing flow rather than engaging some sort of friction or mechanical lock.
Sorry if I'm not clear.

bernhardine · Jan 26, 2020

JRaf said:
...
The question remains: if I lift an implement with the 3pt hitch and lock down the drop speed knob, and that implement doesn't drop down over an extended period, then the 3pt piston/cylinder system is holding pressure and working properly. Right?

YES

The drop speed control is a simple "Throttle check valve" . The check valve blocks the oil-flow in one line from the cylinder to the system and parallel to this the throttle part regulates that flow in the second line. (all in a tiny valve block).
So if you close that throttlevalve and the 3pt doesn't move down, the cylinder is ok.

North Idaho Wolfman · Jan 26, 2020

JRaf said:
As Roadworthy said, it's the 3pt cylinder in the rockshaft housing and it's a one way system. The piston and cylinder lift and gravity does the rest.
And I agree, there's no detent, or "return to center" position on the 3pt lever. Mine seems to either want to go up or down, not find a spot where the implement just sits still (it used to work perfectly until I started to "repair" things). And as NIW suggests my problem with that might be in the feedback link.
But what I'm trying to do right now is isolate the problem. The question remains: if I lift an implement with the 3pt hitch and lock down the drop speed knob, and that implement doesn't drop down over an extended period, then the 3pt piston/cylinder system is holding pressure and working properly. Right?
I guess I'm trying to confirm that the drop speed control system works exclusively via pressure to the hydraulics, stopping or slowing flow rather than engaging some sort of friction or mechanical lock.
Sorry if I'm not clear.

Yes it just stops the flow of hydraulic fluid from coming out of the cylinder when it's closed. So yes the piston seals are fine.

Go to kubotabooks.com download the WSM and adjust the feedback linkage per the WSM, it sounds like it's your whole problem.

JRaf · Jan 27, 2020

Thanks to all for the responses.

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Conceptual Hydraulic Cylinder Question

JRaf

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bernhardine

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GreensvilleJay

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Roadworthy

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North Idaho Wolfman

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JRaf

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bernhardine

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North Idaho Wolfman

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JRaf

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