Air in the Loader Hydraulics: Kubota Review  -- Kubota Tractors Discussion Forum and Review Air in the Loader Hydraulics: Kubota Review -- Kubota Tractors Discussion Forum

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 12-05-1999, 00:00 Post: 10652
Bruce L



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 Air in the Loader Hydraulics

I am having trouble with air in the hydraulics on my loader bucket. Sometimes when I dump the bucket, I want to spread out what I just dumped. So I leave the bucket rolled forward, lower it down, and drag it across the load that was just dumped. At that point the bucket will roll back as much as 45 degrees because of air in the system. I have tried cycling the cylinders through their full range. I have also tried bleeding the air out of the bucket cylinders by cracking the hose fittings open when the cylinder has flopped back (air compressed). I did get it to spit out some air when I did that but It didn't change things much. Any thoughts on this would be appreciated. I have a triple valve on the back and so far only one set of ports has been used. I am wondering if air in those lines could affect the loader? I don't think so but I am going to try an bleed those too. BL






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 12-05-1999, 00:00 Post: 10656
Roger L.



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 Air in the Loader Hydraulics

Bruce, I'd bet there is nothing wrong with your loader. What you are experiencing will often happen with small loaders when you have a heavy load in the bucket. This is just an educated guess, but what I think is happening is that when a heavy bucket load is dumped or lowered too quickly the fluid in the cylinder will cavitate because the load is rotating the bucket and forcing the oil out of the pressurized side of the cylinder faster than the pump can refill the intake side. When this happens, out-gassing from the fluid will fill the cavitation pocket with air that is normally entrained in the fluid as microscopic bubbles. The effect is similar to an air leak in the line.
You can avoid this problem by moving the bucket slowly and/or simultaneously revving the engine to max. Sometimes inexpensive and/or worn loader spool valves won't allow you to slowly ease a heavily laden bucket down - making the whole problem worse.
Another way to solve the problem if you do have these less-than-best spool valves is to place "restrictor orfices" in the line which reduce the fluid flow and help prevent cavitation by slowing the flow of fluid to and from the cylinders. Your dealer will know about these, but of course they slow down the loader when it is unloaded as well. The higher-dollar solution is to buy a top quality commercial loader dual-spool valve with float. They are very sensitive and accurate at partial openings. Nice and controllable. But they are at least double the price of the common spool valves.
Or you can do nothing. That works. The cavitation doesn't seem to hurt anything, and raising the empty bucket and running through the cycle a few times at full revs will put the bubble back into solution. Roger L.






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 12-05-1999, 00:00 Post: 10658
Don in OR



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 Air in the Loader Hydraulics

Bruce, Roger hit it right on the head. Try increasing engine R.P.M. first, A little more throttle may be enough to make your hyd. pump keep up. J.D struggled with this problem and has recently added a regenerative circuit on the SCV's on certain models. To get rig of air once you've got it, cycle the cylinders like you said, but hold pressure at end of stroke for five seconds, both directions. This is called "phasing" the cylinders and should force air and gasses out.Good luck.






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 12-05-1999, 00:00 Post: 10663
Rob



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 Air in the Loader Hydraulics

I have a JD4600 and have never experienced this problem.






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 12-05-1999, 00:00 Post: 10665
Bill



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 Air in the Loader Hydraulics

I have noticed the same problem on my 7300. I also noticed that it would happen when I brought something up (like the york rake) on the 3ph and then would forget and not put the hitch control lever back into neutral. When I would remember to do that, the loader held firm. FWIW. Bill






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 12-05-1999, 00:00 Post: 10674
Bruce L.



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 Air in the Loader Hydraulics

I used to have a John Deere 420 (garden tractor) and the number 44 loader. It behaved exactly the same way. I just put up with it and never really tried for a solution. I expected the new Kubota would work better. I have an old 742 Bobcat that will handle about the same amount of load as the Kubota and it certainly does not behave this way. What is a regenerative circuit? I think I remember about a regenerative circuit being used for hydraulic self leveling.
BL






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 12-06-1999, 00:00 Post: 10685
markchalkley



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 Air in the Loader Hydraulics

A regenerative circuit is one where the fluid coming out of the rod end of the cylinder is "re-generated" by being fed back into the blind end. In effect, it's pressurizing both ends of the cylinder, but because the rod end generates less force (because the rod itself takes up piston surface area), the cylinder still extends. This has the effect of increasing the flow and, therefore, the cylinder motion speed, by approximately the ratio of the rod area to the cylinder area. It has the negative effect of reducing the power available by the same percentage as the flow increase, but this is not usually a problem when used with bucket dump applications. A "regenerative" circuit would obviously be a very big mistake on the roll-back side. Note, too, that regenerative circuits only work in one direction, i.e. when the cylinder is being extended. If you tried to use it the other way around, the cylinder motion would still be to extend the cylinder. The only uses of regenerative circuits, as far as I know, is to speed up cylinder motion, and to make life difficult for us hydraulics hobbyists (as in the case of when you're trying to use an electrically actuated valve to allow the roll-back & dump circuit to also control a 4-in-1 bucket)...






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 12-07-1999, 00:00 Post: 10706
tom



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 Air in the Loader Hydraulics

There was a discussion about bleeding hydrolic lines this summer (maybe on this board). The person with the problem responded to a suggestion by saying that
he couldn't bleed the hydrolic lines because he didn't have an air compressor.

I'm curious if the comment makes sense, or in what way an air compressor can be
used to bleed hydrolic lines.

Thanks for any information.






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 12-07-1999, 00:00 Post: 10716
Roger L.



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 Air in the Loader Hydraulics

Because the tractor hydraulics are a full flow type of system as opposed to a more static system like hydraulic brakes, bleeding them is not necessary. The flow will sweep out most air, and any air problem is more likely to be from air entrained into the fluid by the thrashing of the pump, cavitation, and return splash. Not much you can do about that. Cycling the loader when the oil is hot is the best way that I know of. I'd be interested in hearing if anyone has found a reason to bleed the tractor hydraulics. I can't see any reason that an air compressor would be necessary, but there are always new tricks to learn.






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Discussion Boards > Active Subjects > Messages as Posted > Kubota Review Forum

Thread 10652 Filter by Poster:
Bill 1 | Bruce L 1 | Bruce L. 1 | Don in OR 1 | markchalkley 1 | Rob 1 | Roger L. 2 | tom 1 |

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