Kubota Hydraulic Info and Q/A

[TheOldHokie]

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.


I will start by telling you that the pump produces a constant flow of oil which must always have a way to circulate. If it does not the pump is deadheaded and catastrophic damage is immediate.

Keeping 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"

Now let the discussion begin!!

Dan

 

[Grandad4]

Great idea! Keep going, please.

 

[xrocketengineer]

Fantastic! I am assuming that the 3rd Function valve in the diagram is not a "bypass valve" and the Position Valve Control refers to the three point hitch control. Is that right?

 

[Joisey]

Fantastic idea. If one is unfamiliar with hydraulics or has limited knowledge, an illustration can make a world of difference. Even for those that are familiar with hydraulics, the diagram will make a good way to double check how things work.

 

[TheOldHokie]

Fantastic! I am assuming that the 3rd Function valve in the diagram is not a "bypass valve" and the Position Valve Control refers to the three point hitch control. Is that right?

Good kickoff question

Lets assume the 3rd function valve is a 4 way solenoid operated directional control valve with tandem center spool. That is what Kubota and third party suppliers use in their kits.

The loader valve is Kubota OEM with all the factory's "special features".

The position control valve is synonymous with 3pt control valve.

Dan

 

[Russell King]

Please explain what T port does on the loader (FEL) valve.

 

[Russell King]

Please explain what the PB (power beyond) port does and why it is (usually) installed in a T (Tank Return) port.

 

[Russell King]

Please provide a description of the valve port names and any additional names (ie HPCO v PB).

You may want to expand the loader valve diagram to show the flow through the valve when passive and when diverting to a cylinder?

 

[TheOldHokie]

Please explain what T port does on the loader (FEL) valve.

Nice softball and I am not going get sucked into the full complicated answer. We will save that for graduate classes

When the spool in the loader valve is shifted:

1. The neutral circuit is blocked at PB,
2. The oil coming in on the neutral circuit is rerouted to the loader cylinder(s).
3. Oil coming back from the cylinder(s) is sent out the tank port and goes directly back to the sump.

TEASER: that is "standard" behavior but on current generation Kubota valves that is only true for the bucket roll back function

 

[TheOldHokie]

Please provide a description of the valve port names and any additional names (ie HPCO v PB).

You may want to expand the loader valve diagram to show the flow through the valve when passive and when diverting to a cylinder?

Thats exactly what I am attempting to avoid. My intent here is to focus on one specific thing at a time. Hopefully that will develop logically.

Broad complicated questions and answers overwhelm and confuse people. Lets stick to softballs and no curves like you tossed on that first one That question and answer covered a basic behavior in simple terms that anyone should be able to understand. Lets try to keep it that way.

Dan