Kubota Hydraulic Info and Q/A

[TheOldHokie]

Are there standard colors used for explanation of hydraulic diagrams for the purpose of instruction? For example, I might have chosen blue for the general, flowing circuit, perhaps green for the return tank, and maybe be saved red to illustrate working parts of the circuit when they’re activated.

Just curious and nothing more.

No. But red is usually indicative of elevated pressure and blue of low or no pressure. In my description I identified the two colors and circuits by name and made a point of stating both sections where at zero pressure. To date nobody has asjed anything about pressure .

Dan

 

[OntheRidge]

Thank you for this thread!

 

[Workerbee]

The mods really should pin this to the top

 

[Paul Allwood]

The PB (power beyond) port is used to supply high pressure oil to a down stream valve. Power beyond separates low pressure tank return oil from high pressure carry over oil. The mechanics of how that is done and why you want to do it is an advanced topic for later discussion. In general the PB port is just the continuation of the neutral circuit.

Dan

Why does high pressure oil go from the third function valve T port to the position control P port rather than from a PB port on the third function valve ? I don't understand why they are different.

 

[Old_Paint]

Why does high pressure oil go from the third function valve T port to the position control P port rather than from a PB port on the third function valve ? I don't understand why they are different.

That, I can answer because I am well versed in the annoyance with this particular valve .. The 3rd function valve in nearly all kits is a 4 port 3-position open center valve. There is no PB function in the valve. The ports are P,T,A, and B, When de-energized (or normal position) the P Port is directly connected (Open) to the T port to allow oil flow downstream. Activating the valve in either direction will connect the P (pressure) port to either the A or B port and the other will be connected to the T port to drain the opposite side of a cylinder circuit. A recent failure of the control switches on my 3rd function has renewed my interest in a real solution, because when the cylinders stroke fully, it’s the same thing as deadheading the pump output which results in extremely high temperatures in the hydraulic fluid in a very short time and a complete loss of other hydraulic functions. If you aren’t paying attention, you could have a catastrophic failure.

This is a discussion I started with the thread creator in another thread about 3rd function valves. OH is a smart dude, so pay attention.

Thanks OH for your volunteer service in this subject.

 

[TheOldHokie]

Why does high pressure oil go from the third function valve T port to the position control P port rather than from a PB port on the third function valve ? I don't understand why they are different.

Now we are getting the kind of QUESTION I was looking to stimulate. This is not goung to be a short respinse so please trg to read carefully and be patient.

The answer of why and how is more than a little complicated. But the important thing to understand is in both cases its still the same high pressure flow coming from the pump. but its managed differently.

When the loader valve is operated it shuts the NEUTRAL flow out PB off and directs it to the cylinder. The return oil from the cylinder is sent back out the tank port which is cinnectef to the TANK circuit and the fliw it goes STRAIGHT BACK TO THE SUMP.

The 3rd function valve shuts the NEUTRAl flow off and routes it to the cylinder just lIke the loader valve and the return oil is routed out the TANK port. But here the tank port is connected to the NEUTRAL circuit and the return flow is reintroduced imto the NEUTRAL circuit where it goes to the next valve. At first blush that seems like a good/better idea but there is a hydraulic fly in that ointment.

THE 3RD FUNCTION CYLINDER AND ITS LOAD IS NOW IN THE NEUTRAL CIRCUIT.

This is problematic for multiple reasons. For one, if a down stream valve is activated at the same time as the 3rd function valve the load on the 3rd function cylinder is going to reduce the amount of force the down stream cylinder can generate. Likewise the load on the down stream cylinder is being added to the 3rd function cylinder reducing the amount of force the 3rd function can produce.

In summary.

The loader valve blocks the NEUTRAL circuit and isolates the loader cylinders from any down stream loads

The third function valve does not block NEUTRAL but it puts the cylinders in the middle of the NEUTRAL circuit causing what can be troubling interactions.

I am going to stop there and let everyone mull on that. If you are a hydraulic novice this is probably confusing and hard to wrap your head around.

Paul, thanks for the simple unadorned question. It gets us to a fundamental concept and its exactlg how I was hoping to let reader questions guide the discussion. I am sure you have follow on questions so as soon as you think you have a solid understanding of this concept lets proceed with one of them.

Dan

 

[TheOldHokie]

That, I can answer because I am well versed in the annoyance with this particular valve .. The 3rd function valve in nearly all kits is a 4 port 3-position open center valve. There is no PB function in the valve. The ports are P,T,A, and B, When de-energized (or normal position) the P Port is directly connected (Open) to the T port to allow oil flow downstream. Activating the valve in either direction will connect the P (pressure) port to either the A or B port and the other will be connected to the T port to drain the opposite side of a cylinder circuit. A recent failure of the control switches on my 3rd function has renewed my interest in a real solution, because when the cylinders stroke fully, it’s the same thing as deadheading the pump output which results in extremely high temperatures in the hydraulic fluid in a very short time and a complete loss of other hydraulic functions. If you aren’t paying attention, you could have a catastrophic failure.

This is a discussion I started with the thread creator in another thread about 3rd function valves. OH is a smart dude, so pay attention.

Thanks OH for your volunteer service in this subject.

Read my response to Paul. The deadheading you describe can and does occur in both scenarios. Your analysis is incorrect/incomplete and you need to think harder about what is causuling the deadheading. Its not power beyond versus tank. Feel free to ask a follow on question if you still dont understand why thats the case.

Dan

 

[Old_Paint]

Read my response to Paul. The deadheading you describe can and does occur in both scenarios. Your analysis is incorrect/incomplete and you need to think harder about what is causuling the deadheading. Its not power beyond versus tank. Feel free to ask a follow on question if you still dont understand why thats the case.

Dan

What happened with my 3rd function is the button to close the clamp failed energizing the valve. Once the cylinders were fully stroked, the neutral circuit was blocked because there was no downstream flow beyond the cylinders. Whether it’s a failed valve blocking the flow or the cylinders being fully stroked , the result is the same, blocked neutral flow, if there is no flow from the T port of the 3rd Function valve. Since the T port of the 3rd Function valve is the continuation of the Neutral circuit, the label of the T port is a misnomer because it really has no connection back to tank.

Not much rethinking needed on the symptoms. The neutral line was definitely dead heading and loading the engine with nothing but the Pressure Relief on the pump. It’s not a pretty sound. I think we’re saying the same thing, but using different words. The one thing I always noticed was the number of different things the same object can be called in hydraulic systems. What you call the Neutral circuit I learned as the Pressure circuit. From a hydraulics engineer.

 

[TheOldHokie]

What happened with my 3rd function is the button to close the clamp failed energizing the valve. Once the cylinders were fully stroked, the neutral circuit was blocked because there was no downstream flow beyond the cylinders. Whether it’s a failed valve blocking the flow or the cylinders, the result is the same, blocked neutral flow, if there is no flow from the T port.

Not much rethinking needed on the symptoms. The neutral line was definitely dead heading and loading the engine with nothing but the Pressure Relief on the pump. It’s not a pretty sound.

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

 

[TheOldHokie]

What happened with my 3rd function is the button to close the clamp failed energizing the valve. Once the cylinders were fully stroked, the neutral circuit was blocked because there was no downstream flow beyond the cylinders. Whether it’s a failed valve blocking the flow or the cylinders being fully stroked , the result is the same, blocked neutral flow, if there is no flow from the T port of the 3rd Function valve. Since the T port of the 3rd Function valve is the continuation of the Neutral circuit, the label of the T port is a misnomer because it really has no connection back to tank.

Not much rethinking needed on the symptoms. The neutral line was definitely dead heading and loading the engine with nothing but the Pressure Relief on the pump. It’s not a pretty sound. I think we’re saying the same thing, but using different words. The one thing I always noticed was the number of different things the same object can be called in hydraulic systems. What you call the Neutral circuit I learned as the Pressure circuit. From a hydraulics engineer.

I see you edited your original post so let me respond to the edits. I am doing it in a new post to keep the chronology clear.

Different names for the same thing is a part of the english language and can be a real obstacle to technical discussions. My intent in this discussion is to define clear naming conventions just as a technical writer would do in a formal publication. Thats my formal training and how I would like to roll in this informal discussion.

Forvopen center hydraulic systems the term neutral circuit is used to unambiguously identify the path taken by pumped oil when all valves in the serial " daisy chain" are in neutral. I made my preference for that terminology clear in the opening post and its one that is universally understood and used in the engineering community. Inherent in that term is the understanding that the neutral circuit is akways at ZERO pressure when the circuit is in the "standby " state. I have edited my introductory post to emphasizlse that.

You and your hydraulic engineer friend are certainly free to use whatever terms you like in casual conversation but in this discussion please try to be more precise so as to not confuse the other participants. I certainly dont want this discussion to dissolve into debates over semantucs.

Dan

 

[Old_Paint]

Okay, I think I spotted my disconnect.

You’re speaking of the system in ‘NORMAL’ status. In which case I completely agree that the 3FV doesn’t block the neutral flow, because the P and T ports are connected. HOWEVER, if the 3FV is actuated, the neutral flow is certainly interrupted and the 3RD function cylinders will stop all flow through the T port when they fully stroke (assuming they’re not bypassing). The same would be true except sooner with no cylinders connected to the 3FV.


I jumped ahead just a bit because the normal’ status isn’t what gives me headaches. Getting on the same page ain’t easy sometimes.


So for the sake of format:

If the loader valve (when activated) blocks downstream flow in the neutral line, how am I able to simultaneously close the grapple and lower the loader boom (until the grapple cylinders stroke)? I understand why the 3FV stops the loader, but why doesn’t the loader valve stop the 3FV until it stalls? You probably already know what the next question is.

 

[Old_Paint]

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

We’re saying the same thing again.

It wasn’t a short circuit, but a failed micro switch that energized the solenoid, and I’m pretty sure that I said that it deadheaded when the cylinder stroked. The switch is now replaced and the 3FV is working just like it’s designed.

But let’s move along.

Can you post a diagram of the Loader valve?



The design and porting of the FEL valve will allow simultaneous movement of the boom and curl. It is also a proportional valve that allows flow control to control the speed of either function. It includes a float function for the boom and a quick dump for the curl, both of which basically connect the cylinders straight to the tank return line. While in float, the curl function still works. It’s an amazing little valve.

 

[TheOldHokie]

We’re saying the same thing again.

It wasn’t a short circuit, but a failed micro switch that energized the solenoid, and I’m pretty sure that I said that it deadheaded when the cylinder stroked. The switch is now replaced and the 3FV is working just like it’s designed.

But let’s move along.

Can you post a diagram of the Loader valve?



The design and porting of the FEL valve will allow simultaneous movement of the boom and curl. It is also a proportional valve that allows flow control to control the speed of either function. It includes a float function for the boom and a quick dump for the curl, both of which basically connect the cylinders straight to the tank return line. While in float, the curl function still works. It’s an amazing little valve.

I told you - I am not goung to debate semantics.

Once agsin you have made some erroneous conclusions. The Kubota loader valve does not operate as you think it does. Thats all I am going to say here about that valve.

The Kubota loader valve is a complex and specialized design and bears no resemblance to a commodity loader valve which is the starting point I have chosen for this introduction to tractor hydraulics thread.

All the information you are asking for is clearly descrivex complete with detailed svhematics andv color pucyures in the Kubota loader workshop manuals. That discussion is to complex for the "novice" audience here.

If you want to pursue that topic download a loader manual and study it. If you have questions about that content start a thread and ask there. If I see the thread and have an answer i will post it there.

At some point this "novice" thread will come to an end - probably with a discussion of rear remotes and backhoe added to the initial configuration. At that point if there is interest I would consider starting a new thread dedicated to just the Kubota loader valve, its oddities, and the funky problems that arise from them.

Dan

 

[imarobot]

I’m hoping this thread can stay as a hydraulic system operation description and not a specific problem solving discussion.
I’m probably the dumb one in the class but could you please define the parts of a hydraulic system and their function – open center, position control valve, the P PB & T connections, etc. I would like to see block diagrams of the flow of a system performing its function. For example, lowering or raising the FEL loader and curling the bucket kind of thing. Or why does using PB prevent the 3 point hitch from working?
Also in your diagram where is the tank?
Sorry if I am starting at too low on the knowledge scale for your intension of this thread. If so carry on with your intended direction.
Thank you for taking the time to create this thread.

 

[TheOldHokie]

I’m hoping this thread can stay as a hydraulic system operation description and not a specific problem solving discussion.
I’m probably the dumb one in the class but could you please define the parts of a hydraulic system and their function – open center, position control valve, the P PB & T connections, etc. I would like to see block diagrams of the flow of a system performing its function. For example, lowering or raising the FEL loader and curling the bucket kind of thing. Or why does using PB prevent the 3 point hitch from working?
Also in your diagram where is the tank?
Sorry if I am starting at too low on the knowledge scale for your intension of this thread. If so carry on with your intended direction.
Thank you for taking the time to create this thread.

You are exactly my target audience and I am doing my best to keep it instructional.

You have a pretty big laundry list and my intent is to do all of that but in itty-bitty baby steps so as to not overwhelm the slower members of "the class". Just based on your laundry list I dont think you are in that group.

Let me first address the really simple items on your list and then you can decide where you would like the discussion to go from there.

1. In my drawing the tank is at the pump inlet. I will update that drawing to make that explicit
2. Open center is is a term used to describe a hydraulic system that uses a fixed displacement pump that produces a constant flow of oil. When the flow is not being used to do work the system is in "standby" mode. In standby mode thd pumped oil is constantly circulating in a circular loop that goes through the center of all the control valves. The valves are connected in a serial daisy chain of inlets and outlets. That flow path is called the "neutral" circuit because all the vakves are in the centered (neutral) position. In standby mode the pump and neutral circuit are essentially at zero pressure. I have updated my intrkductory post to try and make it clearer. Please reread it.

Nowbif you have wrapped your head around those basics pick something on your laundry list to cover next. Try to make it something you think is basic rather than complicated.

Dan

 

[imarobot]

Thank you Dan!
My next baby step would be defining what the items I listed above are and how they work. An understanding of what they are will help me better understand and and lead to more questions

 

[TheOldHokie]

Thank you Dan!
My next baby step would be defining what the items I listed above are and how they work. An understanding of what they are will help me better understand and and lead to more questions

I thought I had already defined those terms implicity if not explicitly but I will revist it.

Dan

 

[TheOldHokie]

Thank you Dan!
My next baby step would be defining what the items I listed above are and how they work. An understanding of what they are will help me better understand and and lead to more questions

Let me hit P, T and PB, These are port labels found on control valves

P - identifies the inlet port on the valve

PB - identifies an outlet port that iz used supplies pressurized oil to down stream valves. It is synonymous with N

T - identifies an outlet port that receives oil returned from cylinders and motors. On a valve that does not have a PB or N port the T port also receives pressurized oil from the P port. The T port is typically connected directly to the hydraulic reservoir but in some cases it can be used like a PB port.

Chew on that - I suspect you will want additional clarification

Dan

 

[Russell King]

I will try to ask a few related questions about the Power Beyond sleeve or port that may help with understanding its functionality. But some statements first

Some valves require a PB sleeve, some valves require an internal plug to be installed. That is dictated by the valve manufacturer. It is best to buy the PB sleeve or plug when you buy the valve (If you need it).

Not all valves require a PB sleeve or plug to be installed.

What function does a PB sleeve do?

Does the PB sleeve separate flow or separate pressure?

How does the PB sleeve protect the valve (it is installed in) from damage?

What could be damaged inside the valve if no PB sleeve is installed?

Why does a back hoe valve not require a PB sleeve?

 

[TheOldHokie]

I will try to ask a few related questions about the Power Beyond sleeve or port that may help with understanding its functionality. But some statements first

Some valves require a PB sleeve, some valves require an internal plug to be installed. That is dictated by the valve manufacturer. It is best to buy the PB sleeve or plug when you buy the valve (If you need it).

Not all valves require a PB sleeve or plug to be installed.

What function does a PB sleeve do?

Does the PB sleeve separate flow or separate pressure?

How does the PB sleeve protect the valve (it is installed in) from damage?

What could be damaged inside the valve if no PB sleeve is installed?

Why does a back hoe valve not require a PB sleeve?

This is an introduction for beginners. At this point I think its sufficient to just explain the difference in flow paths through a valve with a power beyond circuit and one without.

I have already jumped ahead and touched on the main think thing happens when you use the T port on a non-power beyond valve for high pressure carry over. So far we have focused on the neutral and tank circuits. I expect to present a more detailed look at those flow paths as part of a general explanation of directional control valved snd their work circuits

Dan