Normal Kubota Rear Float-Detent Valve Operation?

[BCrouse]

I have been having discussions with my dealer, and the dealer with Kubota about what constitutes "normal valve" operation with the Kubota float-detent valves. This is on a Kubota MX5200 with (3) rear remote valves. (1) Standard sping to center valve (2) float detent valves. The hydraulic toplink in the video is a generic 2.5x14 cylinder with a 1.5" rod. It has an operational max pressure of 3000psi and a column load of 14,700lbs. The tested bypass pressure on the rear remotes, the tractor by-pass, was 2500psi.



Video1 (Kubota Float Detent Valve Operation 1 - YouTube) is after setting the length of the toplink using the 澱ump method with the 3rd position float-detent valve and then driving to the lower pond area. A 2min drive. The toplink compressed ~1? It does not fully compress, but it does compress.



Video2 (Kubota Float Detent Valve Operation 2 - YouTube) is another 5mins after Video1. The toplink compresses about 2 now.


I did the same test with the standard valve. While it was not as drastic, it did move a little bit after the 2min then +5mins after than. I was pressed for time and did not get a chance to video it. 2mins it moved ~1/8 and then +5min it moved about ~1/4? This behavior is not something I noticed before, possibly because it is a lot less noticeable compared to the float-detent valves. It confuses me as I have never seen it move before.


The "bump method" mentioned above is how the dealer explained how to set the length of the toplink. Put the implement down, then with pressure on the implement, "bump" the hydraulic remote control to re-pressurize the valve and cylinder.


I still do not consider any of the above "normal" but that is what Kubota is saying is "normal". Can anyone else provide some input as to their experience with the operation of Kubota float-detent valves? Kubota also stated this is how ALL of their float detent valves will operate due to some bleed-by, pressure by-pass that was purposely engineered into the valve (?). It sounded more like lower tolerance allowing pressure to leak, than a truly engineered function but that was their answer.

 

[Leejohn]

You just have a little air in the system.

 

[KWentling]

You just have a little air in the system.

I agree. You need to fully stroke the cylinder each way and hold the lever a few seconds after the end of the stroke to push the air out. Do that a couple of times each way until the cylinder firms up.

 

[BCrouse]

Good thoughts. I thought it was air in it too because it behaves like that. Its been fully cycles numerous times and it still does it.

 

[MtnViewRanch]

Good thoughts. I thought it was air in it too because it behaves like that. Its been fully cycles numerous times and it still does it.

After looking at the videos, there is NO DOUBT in my mind that there is air in the system. A hydraulic cylinder full of fluid does not bounce back and forth as yours does in the videos.

When you say numerous times, how many times is that? Typically 5-10 complete cycles will eliminate most if not all of the air in the cylinder. But for whatever reason, there are times when it takes more than that, and again, full complete extend-retract cycles.

As far as checking your current top link, with an implement attached and on the ground, retract the top link all the way. Un plug the couplers, raise the 3pt hitch. See how far the unit extends on it's own in 15 minutes, then after 1 hour. I would bet that it is minimal (1/4" or less) at the most. If it is more, than good, the cylinder is at fault and is easily repaired. Although being new, I really doubt that the cylinder is at fault, but it can and has happened.

 

[s219]

Definitely air -- it's acting like a spring and hydraulic fluid is incapable of doing that.

 

[BCrouse]

After looking at the videos, there is NO DOUBT in my mind that there is air in the system. A hydraulic cylinder full of fluid does not bounce back and forth as yours does in the videos.

When you say numerous times, how many times is that? Typically 5-10 complete cycles will eliminate most if not all of the air in the cylinder. But for whatever reason, there are times when it takes more than that, and again, full complete extend-retract cycles.

As far as checking your current top link, with an implement attached and on the ground, retract the top link all the way. Un plug the couplers, raise the 3pt hitch. See how far the unit extends on it's own in 15 minutes, then after 1 hour. I would bet that it is minimal (1/4" or less) at the most. If it is more, than good, the cylinder is at fault and is easily repaired. Although being new, I really doubt that the cylinder is at fault, but it can and has happened.

Hi Brian,

Ive cycled it numerous times on numerous remotes. Id say over 100 times at this point. I realize that each time I disconnect and reconnect, it gets a little air in it and I cycle it a few times 3-4 when connecting to new remote.

Ill try the test with the cylinder.


If air is getting in, where would air get in but fluid not get out? I don't have any external leaks....

 

[BCrouse]

Well I did the cylinder test. When I had the cylinder fullly retracted, with the implement on the ground, shut the tractor off. I couldnt get the hydraulic lines to disconnect without cycling the remote handle to remove pressure. The cylinder extended out when I did this. Even with ~5-6 of the cylinder extended out, while in the air under tension unhooked from the remotes, it only extended another 1/8-1/4? I used a zip tie to mark the start. The amount of cylinder exposed on the other side of the ziptie is less than the width of the zip tie. I left it sit about 2.5hrs.

 

[MtnViewRanch]

Well I did the cylinder test. When I had the cylinder fullly retracted, with the implement on the ground, shut the tractor off. I couldnt get the hydraulic lines to disconnect without cycling the remote handle to remove pressure. The cylinder extended out when I did this. Even with ~5-6 of the cylinder extended out, while in the air under tension unhooked from the remotes, it only extended another 1/8-1/4? I used a zip tie to mark the start. The amount of cylinder exposed on the other side of the ziptie is less than the width of the zip tie. I left it sit about 2.5hrs.

Based on the amount of movement that you had, it IS NOT any of the cylinder seals.

 

[BCrouse]

Based on the amount of movement that you had, it IS NOT any of the cylinder seals.

So if there is air getting into the system, would it effect the rear remotes more than the other hydraulic functions? (3pt, loader lift, loader curl, 3rd function)

With the rear remote in neutral, Should I expect more and more air to get pushed into the cylinder and cause it to collapse more and more as time went on?



I'm still not sure how to check if the hydraulic fluid is getting foamy without a dipstick. The MX only has a sight glass. Should I be able to look down the fill hole in the back and see the fluid?