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