Kubota Hydraulic Info and Q/A

[jjb01016]

Thanks for starting this thread! I'm at the level of learning the very basics here as well, so I'll make a post at that level which may be useful for others.

After reading through the first post here a couple of times, I found it REALLY useful to just pull out the WSM manual view of my loader hydraulic circuit, and then go out to my loader control valve on the tractor and compare the two. How can you troubleshoot your hydraulics if you don't even know where the components of the circuit are on your tractor, and how to identify them, right!?!? Fundamentals.

OK, so already between OldHokie's post and doing the above, I'm starting to get a better feel for how the system is laid out.

Here's the LA1154 loader hydraulic diagram from my M7060, which as expected looks a bit like OldHokie's post. You'll see the "P", "T", "PB", and also the feeds and returns to the boom and bucket cylinders marked A1/A2/B1/B2:




...And if I go out to my tractor's loader control valve, whatdya know! I find the same labels:



Hey! That was easy! Sometimes you just need a thread like this to start you down the path. Now I'm going to trace out the next path of my hydraulics to the 3pt hitch, 3rd function and remotes as well. I suggest that anyone reading this thread who is curious but hasn't just traced out the physical hydraulic circuit, go do so!

 

[Old_Paint]

Thanks for starting this thread! I'm at the level of learning the very basics here as well, so I'll make a post at that level which may be useful for others.

After reading through the first post here a couple of times, I found it REALLY useful to just pull out the WSM manual view of my loader hydraulic circuit, and then go out to my loader control valve on the tractor and compare the two. How can you troubleshoot your hydraulics if you don't even know where the components of the circuit are on your tractor, and how to identify them, right!?!? Fundamentals.

OK, so already between OldHokie's post and doing the above, I'm starting to get a better feel for how the system is laid out.

Here's the LA1154 loader hydraulic diagram from my M7060, which as expected looks a bit like OldHokie's post. You'll see the "P", "T", "PB", and also the feeds and returns to the boom and bucket cylinders marked A1/A2/B1/B2:

View attachment 176917 View attachment 176925


...And if I go out to my tractor's loader control valve, whatdya know! I find the same labels:
View attachment 176926
View attachment 176919 View attachment 176920 View attachment 176921

Hey! That was easy! Sometimes you just need a thread like this to start you down the path. Now I'm going to trace out the next path of my hydraulics to the 3pt hitch, 3rd function and remotes as well. I suggest that anyone reading this thread who is curious but hasn't just traced out the physical hydraulic circuit, go do so!

Thanks for the diagram.

 

[Old_Paint]

In the opening post you said that all the circuits are "basically at zero pressure" when the system is in "Neutral" state. What makes the pump suddenly decide to boost pressure/flow? I already know the answer to this from working around industrial pumps in the metals industries but figured someone else might want to know as well. This is your baby, though.

 

[Old_Paint]

When the loader valve is actuated, does it completely close off the PB, or does it only close it partially?

I ask this because I can open the grapple clamp, curl forward , and lower the boom simultaneously, or open, raise, and curl back, but only as long as nothing is at end of stroke. I've learned to do this when moving brush and a little bit of timing goes a long way to avoiding the jerking when the grapple cylinders stall. If the PB was completely shut off by the loader valve as you stated, I could not use the 3FV simultaneously.

 

[Old_Paint]

Is there secondary pressure relief in the loader valve that protects the structure of the loader boom from being overloaded to catastrophic failure?

 

[TheOldHokie]

Is there secondary pressure relief in the loader valve that protects the structure of the loader boom from being overloaded to catastrophic failure?

When the loader valve is actuated, does it completely close off the PB, or does it only close it partially?

I ask this because I can open the grapple clamp, curl forward , and lower the boom simultaneously, or open, raise, and curl back, but only as long as nothing is at end of stroke. I've learned to do this when moving brush and a little bit of timing goes a long way to avoiding the jerking when the grapple cylinders stall. If the PB was completely shut off by the loader valve as you stated, I could not use the 3FV simultaneously.

I was trying to avoid this discussion because Kubota loader valves are atypical. Looks like thats not going to be possible.

The generic answer is it depends on the valve. Some have less overlap on the glands than others. Some valves have metering grooves on the glands and others do not. But in general its best to consider it closed off.

Kubota valves actually have a serial boom spool and return oil is reintroduced into the neutral circuit just like the 3rd function valve. For boom operations "PB" is never shut off.

The bucket spool is fed by the serial neutral flow from the boom and that allows the bucket and boom to move in lockstep regardless of differences in loads. That makes synchronized operations very smooth but puts the boom and bucket cylinders in series which reduces the force available to each function. So much so that Kubota says you should not lift and curl at the same time. That slot is usually blank on the joystick position diagram. I say Phooey on that!!!

Curl returns to tank and there is no return on the fast dump.

Putting all that together makes it very difficult to judge gland overlaps. PB flow and the ability to operate the 3rd function simultaneously depends greatly on the combined states of the two spools. If you had a manual spool on the 3rd functjon I think you would find its not nearly as easy to meter as it appears with the super fast all or none electric valve. I will also add its not just end of stroke that causes problems. With the serial boom spool anything that stalls the boom creates a deadhead state and stalls the entire hydraulic system front to back. Full dump or roll has the same effect on everything diwn stream of the loader.

The loader valve has an inlet pressure relief but if its set lower than the system relief it reduces pressure to the entire hydraulic system. E.g loader, 3pt, aux vakves remotes, and backhoe I dont know what Kubota says but my advice ls it should be set higher than the tractor which means its never going to activate.

All of this is covered in great detail in the loader WSM. Thats what you should be reading.

Now back to basics.

Dan

 

[rfcomm2k]

To the admins - if this is out of line or inappropriate please delete it.

I am starting this thread to give folks a chance to learn the basics of Kubota tractor hydraulics. Its the number one topic here and multiple people have asked for something of this sort. Its an open discussion. Feel free to ask questions and provide answers. If you are providing answers make sure you are speaking fact not fiction. Public flogging of purveyors of missinformation is encouraged and that includes me!!

Please keep questions and answers short​

I am going to start things off with something simple. Here is a diagram of an open center circuit similar to the loader and third function on a Kubota tractor. Its the source of much confusion. Ask a question and I or someone ekse will try to answer it. One question at a time and keep the question short and specific.

View attachment 176908

I will start the discussion with a few fundamental concepts. The pump produces a constant flow of oil which must always have a way to circulate. If it does not the pump is deadheaded, pressure spikes way above the limits if the components and catastrophic damage is immediate.

Because deadheading means instant death my diagram has a pressure relief valve right at the pump outlet. This valve acts as an over pressure safety device. It is normally closed but in the event something in the circuit deadheads the pump the relief opens at a predetermined max safe pressure setting and oil is diverted to the tsnk circuit and from there back to sump to prevent pressure from going any higher. The relief remains open until the deadhead condition is removed and pressure drops. At that point the relief returns to the closed state.

Keeping all that in mind, with ALL valves in neutral ALL oil flows continuously around the outer circle. Red is called the neutral circuit and blue is called the tank circuit. Please be precise when using those terms.

In this state pressure in both the neutral and tank circuits is "zero". This state is often called "standby" and the only work the pump is doing is circulating free oil and pressure in the neutral circuit is essentially zero. Now two very important concepts.

PRESSURE IN THE NEUTRAL CIRCUIT ONLY GOES HIGH WHEN A VALVE IS SHIFTED AND THE PUMP IS USED TO DO WORK

Similarly

PRESSURE IN THE TANK CIRCUIT IS ALWAYS ZERO.

Burn those two very important concepts into your brain and let the discussion begin!!

Dan

I have a Kubota K008 mini excavator. It does not travel more than a foot per minute forward or back. I had an issue with the suction filter in the hydraulic tank (it disintegrated into pieces) so I drained the hydraulic system as much as I could and replaced both filters and put in NEW fluid. Everything still functions well except travel (no change). Took the two hoses off one travel motor, capped off hose from bottom of motor and aimed other into a bucket. Good flow happening, but it is flowing constantly, not just when I push the lever. When I push lever I get good flow with more pressure, and lever in other direction results in less flow, but not significantly less. Swapped hoses and got very little flow pushing lever in one direction and NO flow in other direction. Same test on other motor same results.
Is it normal for a travel motor to have fluid flowing thru it constantly?
I expected no flow unless lever is moved, then one hose should flow very well and other be a return. When lever is pushed in other direction the hoses should change functions.
As I was letting hose pump into a bucket during this test I found bits of the old suction filter plastic/paper element in bottom of bucket.
So does anyone here have an idea for me?

 

[TheOldHokie]

I have a Kubota K008 mini excavator. It does not travel more than a foot per minute forward or back. I had an issue with the suction filter in the hydraulic tank (it disintegrated into pieces) so I drained the hydraulic system as much as I could and replaced both filters and put in NEW fluid. Everything still functions well except travel (no change). Took the two hoses off one travel motor, capped off hose from bottom of motor and aimed other into a bucket. Good flow happening, but it is flowing constantly, not just when I push the lever. When I push lever I get good flow with more pressure, and lever in other direction results in less flow, but not significantly less. Swapped hoses and got very little flow pushing lever in one direction and NO flow in other direction. Same test on other motor same results.
Is it normal for a travel motor to have fluid flowing thru it constantly?
I expected no flow unless lever is moved, then one hose should flow very well and other be a return. When lever is pushed in other direction the hoses should change functions.
As I was letting hose pump into a bucket during this test I found bits of the old suction filter plastic/paper element in bottom of bucket.
So does anyone here have an idea for me.

My immediate thought is you need to determine what sort of hydraulic system you have.

Your excavator may well have some sort of closed center system which is an entirely different animal than the open center system we are discussing here.

Dan

 

[rfcomm2k]

My immediate thought is you need to determine what sort of hydraulic system you have.

Your excavator may well have some sort of closed center system which is an entirely different animal than the open center system we are discussing here.

Dan

How can I determine what type of system I have?

 

[TheOldHokie]

How can I determine what type of system I have?

Work Shop Manual

 

[scotty73]

To the admins - if this is out of line or inappropriate please delete it.

I am starting this thread to give folks a chance to learn the basics of Kubota tractor hydraulics. Its the number one topic here and multiple people have asked for something of this sort. Its an open discussion. Feel free to ask questions and provide answers. If you are providing answers make sure you are speaking fact not fiction. Public flogging of purveyors of missinformation is encouraged and that includes me!!

Please keep questions and answers short​

I am going to start things off with something simple. Here is a diagram of an open center circuit similar to the loader and third function on a Kubota tractor. Its the source of much confusion. Ask a question and I or someone ekse will try to answer it. One question at a time and keep the question short and specific.

View attachment 176908

I will start the discussion with a few fundamental concepts. The pump produces a constant flow of oil which must always have a way to circulate. If it does not the pump is deadheaded, pressure spikes way above the limits if the components and catastrophic damage is immediate.

Because deadheading means instant death my diagram has a pressure relief valve right at the pump outlet. This valve acts as an over pressure safety device. It is normally closed but in the event something in the circuit deadheads the pump the relief opens at a predetermined max safe pressure setting and oil is diverted to the tsnk circuit and from there back to sump to prevent pressure from going any higher. The relief remains open until the deadhead condition is removed and pressure drops. At that point the relief returns to the closed state.

Keeping all that in mind, with ALL valves in neutral ALL oil flows continuously around the outer circle. Red is called the neutral circuit and blue is called the tank circuit. Please be precise when using those terms.

In this state pressure in both the neutral and tank circuits is "zero". This state is often called "standby" and the only work the pump is doing is circulating free oil and pressure in the neutral circuit is essentially zero. Now two very important concepts.

PRESSURE IN THE NEUTRAL CIRCUIT ONLY GOES HIGH WHEN A VALVE IS SHIFTED AND THE PUMP IS USED TO DO WORK

Similarly

PRESSURE IN THE TANK CIRCUIT IS ALWAYS ZERO.

Burn those two very important concepts into your brain and let the discussion begin!!

Dan

I have ABX2350 and it keeps blowing the hydraulic filter seal. I have cleaned the charge relief valve. The screen and double check to make sure that there was only one oil seal on the filter.\n And it keeps doing it I use Kubota filter, komoda oil and it keeps doing it.What am I missing

 

[TheOldHokie]

I have ABX2350 and it keeps blowing the hydraulic filter seal. I have cleaned the charge relief valve. The screen and double check to make sure that there was only one oil seal on the filter.\n And it keeps doing it I use Kubota filter, komoda oil and it keeps doing it.What am I missing

This "sticky thread" is intended for discussion of general hydraulic theory and operation not trouble shooting individual problems. Please start a new thread in the Normal Threads portion of this forum.

Dan

 

[GeoHorn]

You got the deadheading analysis part right. But you stopped there and somehow jumped to the erroneous conclusion that a valve with power beyond circuitry would somehow avoid the problem. Lets revist that

The deadheading occurrs in the cylinder.

The piston is at end of stroke and unable to move and make room for more oil. There is no path for the incoming oil to get past the piston and on to the T port so pressure on the pump side of the piston increases to the cracking pressure of the safety device which saves the day. The same is true of a valve with a power beyond and tank port. As long as the valve is held open the pump is being deadheaded by the stalled cylinder.

The 3rd function valve experienced an electrical short circuit that caused the electrical actuator on the spool to hold the valve open. Failure of the electrical controls is the culprit, not the internal hydraulic circuitry of the valve.

Dan

I am pleased to see this thread. I also am perplexed how to address my difficulty with it. i don’t want to come-across as being critical of persons…. I only want to create an easier path toward understanding the subject.

(I have a general understanding of mechanics and hydraulics, but from different applications. The problem I am experiencing is due to what I think is a failure to adequately define terms.
The assignation of “P” and “T” can only be assumed to be “pressure” and “tank”.
(but illustrative of the problem: Those terms were not previously defined.… instead we were given “nuetral” and “tank circuit”.
Subsequently, (as in this quoted post) additional terms are introduced which were never defined. (“electrical short circuit” is not explained. Is that an actual electrical current issue? in a liquid hydraulic system? OR…is that a comparative example…. as if hydraulic-oil-flow occurs similarly to electron flows along a conductor? OR…is that an actual electrical short in a physical switch that some tractor implements have?)
I know what a “sump” is…but that term was also not defined… likely because it was assumed EVERYone knew what it means.… But I’m pointing that out because a similar “assumption” is made when the term “power beyond” was never defined either, yet might be ”assumed” it means the same thing to every reader.
Lest anyone think I’m being “silly” or “argumentive”…. Let me point out that tractor hydraulics apparently has a “thing” called a “third function”. To the uninitiated, …WHAT is THAT? It was never defined. Is that part of the loader control/joystick? …or is that some accessory added onto some accessory?

And, I don’t mean to be a “deadhead” …but since we were given permission in Post #1 to flog the teacher: MISINFORMATION has only ONE “S”.

(This post probably is seen as being unnecessarily “picky” …. perhaps even seen as “silly”. But I’m not merely trying to interrupt the learning process…. I’m actually wanting to understand the logic and technicality of tractor hydraulics… and the assumption by the leader and other more-conversant participants leaves me confused when terms are used that were never defined or explained.
if the “third function” applies to a “grapple”…. I don’t own a grapple and have never used one…. but I am interested in how they work and would benefit from such a discussion…. IF the TERMS were defined or explained instead of simply being tosed-out-there.)

Thx.

Carry on.

 

[TheOldHokie]

I am pleased to see this thread. I also am perplexed how to address my difficulty with it. i don’t want to come-across as being critical of persons…. I only want to create an easier path toward understanding the subject.

(I have a general understanding of mechanics and hydraulics, but from different applications. The problem I am experiencing is due to what I think is a failure to adequately define terms.
The assignation of “P” and “T” can only be assumed to be “pressure” and “tank”.
(but illustrative of the problem: Those terms were not previously defined.… instead we were given “nuetral” and “tank circuit”.
Subsequently, (as in this quoted post) additional terms are introduced which were never defined. (“electrical shor circuit” is not explained. Is that an actual electrical current issue? in a liquid hydraulic system? OR…is that a comparative example…. as if hydraulic-oil-flow occurs similarly to electron flows along a conductor?)
I know what a “sump” is…but that term was also not defined… likely because it was assumed EVERYone knew what it means.… But I’m pointing that out because a similar “assumption” is made when the term “power beyond” was never defined either, yet might be ”assumed” it means the same thing to every reader.
Lest anyone think I’m being “silly” or “argumentive”…. Let me point out that tractor hydraulics apparently has a “thing” called a “third function”. To the uninitiated, …WHAT is THAT? It was never defined. Is that part of the loader control/joystick? …or is that some accessory added onto some accessory?

And, since we were given permission in Post #1 to flog the teacher: MISINFORMATION has only ONE “S”.

P and T are labels on ports. What they mean and how they operate is ambiguous.

There are multiple circuits in an open center hydraulic system that operate at elevated pressure. Neutral identifies the route oil takes when ALL actuators are in the neutral (unshifted) position. It is an unambiguous and standard hydrauluc term. used in schematics and technical documents. Thats why neutral not pressure was given as a basic circuit difinition.

Tank was defined as a low (zero) pressure return path to the oil reservoir (aka sump) - also standard nomenclature in hydraulic documentation. Tank is not always synonymous with the T label on a valve port. A perfect example of that is the T port of the 3rd function valve in the basic circuit diageam O posted. It is being used to supply down stream pressure to the three point valve and is in fact a continuation of the neutral circuut.

That diagram and the terms I defined were carefully chosen to illustrate those functional differences. Understsnding those differences is essential to any discussion of the operation of a three port power beyond valve which is a total mystery to most tractor owners.

Its unfortunate but the english language is imprecise and often abused by casual use. Starting with clear well defined terms is the way you cut diwn on the confusion.

Now let me address your confusion over the term "third function" It is a common term for an additional (third) valve used in conjunction with a two function loader valve. What it controls is not nearly as important as understandung its interaction with the neutral and tank circuits.

Dan