Front loader and 3-point hitch slowly drop with or without the engine running

[TheOldHokie]

I'm going to have to bone up on "typical Kubota loader valve" ... I would have thought that the loader valve opens the loader cylinders directly to tank, not power beyond. I'm very interested in the hydraulics plumbing on my tractor, and it's on my to-do list to take another look at the diagrams in the WSM.

A typical valve does but that means all down stream functions are blocked when any spool is shifted.

Kubota is not typical and likes to use a series spool for the lift circuit and a regen spool for the bucket circuit. When the lift spool is shifted the pressure flow goes to one port on the lift cylinder and return flow goes to the power beyond port. That prevents loader lift from blocking down stream valves/cylinders but also puts the loader cylinder in series with the downstream cylinder. Thats what causes the problem where the loader freezes when the 3pt position control feedback system gets out of adjustment and the 3pt does not return to neutral at top of travel. The loader lift cylinder cant exhaust oil because the downstream 3pt cylinder is in series and is stalled.

The loader valve diagrams in the WSM show the flows very clearly.

Dan

 

[ejb11235]

A typical valve does but that means all down stream functions are blocked when any spool is shifted.

Kubota is not typical and likes to use a series spool for the lift circuit and a regen spool for the bucket circuit. When the lift spool is shifted the pressure flow goes to one port on the lift cylinder and return flow goes to the power beyond port. That prevents loader lift from blocking down stream valves/cylinders but also puts the loader cylinder in series with the downstream cylinder. Thats what causes the problem where the loader freezes when the 3pt position control feedback system gets out of adjustment and the 3pt does not return to neutral at top of travel. The loader lift cylinder cant exhaust oil because the downstream 3pt cylinder is in series and is stalled.

The loader valve diagrams in the WSM show the flows very clearly.

Dan

Fascinating! This info will be very helpful when I start looking at the WSM diagrams and hopefully minimize the amount of head-scratching. I learned about regen in the training videos but this will be the first time I've seen them in the wild.

 

[TheOldHokie]

Fascinating! This info will be very helpful when I start looking at the WSM diagrams and hopefully minimize the amount of head-scratching. I learned about regen in the training videos but this will be the first time I've seen them in the wild.

Regen can produce some really weird behaviors

Dan

 

[TheOldHokie]

Fascinating! This info will be very helpful when I start looking at the WSM diagrams and hopefully minimize the amount of head-scratching. I learned about regen in the training videos but this will be the first time I've seen them in the wild.

It is also fascinating to me but we are probably the exception to the rule. Most people really don't want to know the details. They just want to know how to fix something when it is broken.

Here are three diagrams from the LA525 loader WSM that illustrate typical Kubota loader valve operation. It is not the same as a typical off the shelf directional control valve. UP and DOWN are the same circuit just reversed. Bucket DUMP sometimes has a fourth position that is the same as ROLL-BACK. The basic ideas are simple but strange and non-intuitive things happen when the circuits get misconnected or down-stream devices miss-behave. That's when knowing the details of how things work pays dividends in diagnosis.

Its also worth noting that the bucket circuits block power beyond so downstream devices like a third function valve cannot operate at the same time as the bucket cylinders.

Dan

 

[ejb11235]

It is also fascinating to me but we are probably the exception to the rule. Most people really don't want to know the details. They just want to know how to fix something when it is broken.

Here are three diagrams from the LA525 loader WSM that illustrate typical Kubota loader valve operation. It is not the same as a typical off the shelf directional control valve. UP and DOWN are the same circuit just reversed. Bucket DUMP sometimes has a fourth position that is the same as ROLL-BACK. The basic ideas are simple but strange and non-intuitive things happen when the circuits get misconnected or down-stream devices miss-behave. That's when knowing the details of how things work pays dividends in diagnosis.

Its also worth noting that the bucket circuits block power beyond so downstream devices like a third function valve cannot operate at the same time as the bucket cylinders.

Dan

View attachment 82172

View attachment 82173
View attachment 82174

Dan -- it's going to take me a while to digest this. Do you know if Kubota uses the same or similar configuration on the BX23S?

 

[TheOldHokie]

Dan -- it's going to take me a while to digest this. Do you know if Kubota uses the same or similar configuration on the BX23S?

I don't know for sure but Kubota has used regen on most loader dump circuits for some time. They call it fast dump. The serial circuit on the lift was a surprise to me.

Dan

 

[ejb11235]

I don't know for sure but Kubota has used regen on most loader dump circuits for some time. They call it fast dump. The serial circuit on the lift was a surprise to me.

Dan

I'll check out the BX23S hydraulics when I get a chance. I've been spending way too much time on hydraulics for the last few weeks and have been neglecting my work. The fast dump is pretty clever. I haven't noticed an issue when backblading force so I guess they got it right.

 

[ejb11235]

I don't know for sure but Kubota has used regen on most loader dump circuits for some time. They call it fast dump. The serial circuit on the lift was a surprise to me.

Dan

I took a quick look at the WSM (my diagrams are not as clean as yours...do you have a way to get clean BX hydraulic diagrams? if so what's your secret sauce? I've seen discussions about quality of schematics in the PDFs).

It does not appear that the BX23S, (and I presume all the BXs), use a "fast dump" regen. It just dumps to tank.

--eric

 

[TheOldHokie]

I took a quick look at the WSM (my diagrams are not as clean as yours...do you have a way to get clean BX hydraulic diagrams? if so what's your secret sauce? I've seen discussions about quality of schematics in the PDFs).

It does not appear that the BX23S, (and I presume all the BXs), use a "fast dump" regen. It just dumps to tank.

--eric

View attachment 82182

Yep - vanilla circuit.

Dan

 

[mans]

I have a B7200 with B1630 loader and have the same problems. These machines are getting old and worn.

Engine running or not does not matter. The valves still have to seal to hold pressure in the cylinders. The pump does nothing in that regard.

In the case of the loader the control valve is probably shot. Good news is its inexpensive and easy to replace. I'd suggest you make it the number one priority.

Three point is more difficult. That could be either the cylinder leaking or the control valve. The cylinder is easy to service - valve is not. Does the 3pt position control lever stay where its set or does it drop down along with the lift?

Dan

Thanks for the insight on the loader control valve. I have never taken notice of where the 3-point handle is. You have my curiosity going. I will check tomorrow.

 

[TheOldHokie]

Yep - vanilla circuit.

Dan

The pictures I posted are Windows screen shots of the LA525 WSM pdf. I zoom to the largest that will fit on the monitor, hit print screen button, then paste and crop the image using Paint. The BX23 WSM I downloaded from Kubotabooks was a bit fuzzy when I tried that.

Dan

 

[torch]

I'm going to have to bone up on "typical Kubota loader valve" ... I would have thought that the loader valve opens the loader cylinders directly to tank, not power beyond. I'm very interested in the hydraulics plumbing on my tractor, and it's on my to-do list to take another look at the diagrams in the WSM.

I think he's talking about when the spool valve is just shifted partially. Yes, when it is fully open the return flow should be to the tank; when fully closed flow through the spool is from pump to PB, but there may be a bit of overlap as the valve is moved.

 

[TheOldHokie]

I think he's talking about when the spool valve is just shifted partially. Yes, when it is fully open the return flow should be to the tank; when fully closed flow through the spool is from pump to PB, but there may be a bit of overlap as the valve is moved.

In a typical parallel circuit valve with power beyond the spools do not overlap between pump in and power beyond. When the spool is shifted power beyond (CENTER CORE) first closes and flow is shifted to a closed center parallel core that feeds the work ports and load checks. Metering is performed by overlap between that parallel core and the work ports. The spools are stacked in parallel and receiving the same inlet oil flow and pressure via the closed center parallel core.

In the case of the lift spool on the LA525 loader valve the exhaust oil from the cylinders is routed back to the power beyond core rather than tank to power a down stream valve or to tank if the down stream spools are all in neutral.

Dan

 

[mans]

Thanks for the insight on the loader control valve. I have never taken notice of where the 3-point handle is. You have my curiosity going. I will check tomorrow.

Thanks for the insight on the loader control valve. I have never taken notice of where the 3-point handle is. You have my curiosity going. I will check tomorrow.

Thanks to everyone who has contributed to this thread.

A little history on this tractor. It is a working tractor for a nonprofit volunteer-run organization. We have a small orange grove that we use for educational field trips for school kids seeing about 5000 kids a year. I am a volunteer and trying to get the tractor fully up and running. I just completed a cylinder head replacement and now have moved into the hydraulics.

Regarding hydraulics, I have never really done much work with them. I understand the basics and your responses have helped significantly. From the comments, it appears that I should start with the loader control valve.

Looking for an OEM direct replacement for the loader control valve. They seem scarce and very expensive. If I can't find one, will a generic loader valve like this work? Are the hose fittings for the ports SAE or Metric?

Monoblock Hydraulic Directional Control Valve, 2 Spool w/ Single Float Detent, 11 GPM

This Monoblock Hydraulic Directional Control Valve uses 1 Float & 1 "A" Spool. It has a capacity of 11 GPM. Free Shipping

summit-hydraulics.com

 

[TheOldHokie]

Thanks to everyone who has contributed to this thread.

A little history on this tractor. It is a working tractor for a nonprofit volunteer-run organization. We have a small orange grove that we use for educational field trips for school kids seeing about 5000 kids a year. I am a volunteer and trying to get the tractor fully up and running. I just completed a cylinder head replacement and now have moved into the hydraulics.

Regarding hydraulics, I have never really done much work with them. I understand the basics and your responses have helped significantly. From the comments, it appears that I should start with the loader control valve.

Looking for an OEM direct replacement for the loader control valve. They seem scarce and very expensive. If I can't find one, will a generic loader valve like this work? Are the hose fittings for the ports SAE or Metric?

Monoblock Hydraulic Directional Control Valve, 2 Spool w/ Single Float Detent, 11 GPM

This Monoblock Hydraulic Directional Control Valve uses 1 Float & 1 "A" Spool. It has a capacity of 11 GPM. Free Shipping

summit-hydraulics.com

It will work fine but you also need to get the optional power beyond sleeve. The B1630 loader on my B7200 came with a joystick valve so you might want to consider the joystick version of the Summit valve.

Hydraulic Directional Control Valve for Tractor Loader w/ Joystick, 2 Spool (Single Float Spool Optional), 11 GPM

FREE SHIPPING This Monoblock Hydraulic Directional Control Valve uses a Joystick, 2 Spools and has a capacity of 11 GPM. These valves are used to start and stop fluid flow into hydraulic cylinders or hydraulic motors.

summit-hydraulics.com

The ports on my B1630 loader valve are SAE-06 but you may have a different loader and or valve. Its really not an issue since you will need port adapters for the new valve. Just get SAE-08 port adapters to match the new ports to the old cylinder hoses which on mine were male NPT. Same for yhe inley. outlet, and power beyond ports on the Summit valve which are SAE-10. When I replaced the hoses I switched to female JIC swivels which simplify connecting the hoses to the valve and steel lines.

Dan

 

[ejb11235]

The pictures I posted are Windows screen shots of the LA525 WSM pdf. I zoom to the largest that will fit on the monitor, hit print screen button, then paste and crop the image using Paint. The BX23 WSM I downloaded from Kubotabooks was a bit fuzzy when I tried that.

Dan

Thanks. Unfortunately, my WSM, which I think I downloaded from Kubota books, exhibits visual artifacts on the electrical schematics and hydraulic diagrams that's typical of JPG compression on bit-mapped images. BTW, you can use "Snip & Sketch" built into Windows 10 for taking your screenshots and avoid having to crop as a separate step. It also has some annotating tools, such as a highlighters and pens. It might speed up your workflow a little.

 

[ejb11235]

I think he's talking about when the spool valve is just shifted partially. Yes, when it is fully open the return flow should be to the tank; when fully closed flow through the spool is from pump to PB, but there may be a bit of overlap as the valve is moved.

Torch--

To expand on what @TheOldHokie said: "In the case of the lift spool on the LA525 loader valve the exhaust oil from the cylinders is routed back to the power beyond core rather than tank to power a down stream valve or to tank if the down stream spools are all in neutral."

Below are close-ups of the hydraulic diagrams he posted.

• In "UP", the exhausted rod-end fluid is routed to power-beyond.
• In "ROLLBACK" the exhausted cap-end fluid is routed to tank
• In "DUMP", the exhausted rod-end fluid is routed back to the cap-end. While this significantly reduces the force, the extension speed is higher because the cap-end volume is being filled not only by the pump but the fluid getting pushed out of the rod-end.
  • For more info on regenerative extension, check out Jim Pytel's video: Regenerative Extension on YouTube

--eric

---------------------------------------------------------------------------------------------------
UP -- fluid exhausted out of the rod-end is routed to power beyond

---------------------------------------------------------------------------------------------------
ROLLBACK -- fluid exhausted out of the cap-end is routed to tank

---------------------------------------------------------------------------------------------------
DUMP -- regenerative extension