BH77 Hydraulic Concerns

[NewOrangeMan]

I thank you all for your comments and here is an update both from the dealer and my investigation and solution.

The dealer was ignorant to the warning label and stated that they always put the 3rd function auxiliary valve in series after the BH. When questioned about the back pressure in the BH valve body and possible damage they did not think it would be an issue and don't recall seeing any issues for repair.

My research and your comments all point to the BH valve body not being designed for excessive back pressure on the seals. Also, another big item is performance, the tractor flow rate of 5 gpm is seriously restricted through the 3rd function hoses and valve. The BH is setup with 3/8" hard line and hoses for full flow through the valve body. with the 3rd function solenoid and 9 feet of 1/4" hose it was cut about in half while raising the pressure significantly.

Agreeing with what "TheoldHokie" said, I am planning to use the BH to dig stumps and rip bushes then use the grapple to clean up the mess. Since I can't run them both at once, I came up with the following solution.

My solution was to install a solenoid operated diverter valve in the line ahead of the BH to divert the fluid to the 3rd function when needed. I wired the solenoid into the same power switch that provides power to the control buttons for the 3rd function solenoid so when it is on the diverter valve is on. This way no pressure is supplied to the BH while using the grapple and the return lines are free flowing to the HST (tank). The best part is that all I have to do is turn on the power switch and it all happens smoothly without having to get off and move hoses.

I thank you all for your thoughts and insight, I wish there was a Kubota board to submit questions to for factory advise and insight to how these machines were designed and built. As a retired engineer I have already made several changes to suit my needs and requirements, such as this one and some help would be nice sometimes.

 

[DaveMueller]

If/when you remove the BH77, make sure to couple the inlet/outlet hoses on the tractor together.

 

[NewOrangeMan]

Yes, I agree I don't want to dead head the system.

 

[TheOldHokie]

I think you're right. If the 3PH is topped out and calling for more lift, this would create the back pressure on preceding valves. I think some tractors don't have feedback and the linkage on those that do have feedback can be maladjusted .

That would be a poor design. Most 3pts automagically shut down at max lift so as to not subject the pump to maximum pressure for extended periods of time. Even my archaic 9N without position control kicks out at max travel. Can it be miss-adjusted? Sure but that would be something to fix. I would worry far less about that than having the 3rd function or any other valve between the hoe and the 3pt. Every time they are activated the hoe immediately sees the pressure they are producing at the cylinders as tank backpressure.

As I said earlier - Kubota got his right by putting valves with HPCO on the newer hoes.

Dan

 

[TheOldHokie]

Yes, I agree I don't want to dead head the system.

All this chatter is wonderful but have you talked to the dealer about your concerns with the 3rd function they installed? They did it and they should be able to provide a reasonable explanation of why.

Dan

 

[Old_Paint]

I think you're right. If the 3PH is topped out and calling for more lift, this would create the back pressure on preceding valves. I think some tractors don't have feedback and the linkage on those that do have feedback can be maladjusted .

I guess I'm trying to figure out why this would happen. What happened to remove the feedback linkage to stop the 3PH? It's driven by the pitman arms on the lift. They should still be on, but the lift links and lift arms have to be removed to put the BH on.

I'm also trying to see someone using a grapple and a backhoe simultaneously. Not sure how that can be done if the outriggers are down and the FEL has the front lifted for digging. Installed at the same time, sure. Used at the same time, interesting. Backhoes pretty much insist that the tractor's weight is fully on the outriggers and FEL to stabilize the machine, or you'll drag it all over the place with the dipper. If you're pulling with the dipper, the grapple is pointed the wrong way to do any good. If you're pushing with the grapple, I'm hoping the BH is raised, centered, and PINNED in the transport position. If not, you're begging for disaster.

 

[TheOldHokie]

I guess I'm trying to figure out why this would happen. What happened to remove the feedback linkage to stop the 3PH? It's driven by the pitman arms on the lift. They should still be on, but the lift links and lift arms have to be removed to put the BH on.

I'm also trying to see someone using a grapple and a backhoe simultaneously. Not sure how that can be done if the outriggers are down and the FEL has the front lifted for digging. Installed at the same time, sure. Used at the same time, interesting. Backhoes pretty much insist that the tractor's weight is fully on the outriggers and FEL to stabilize the machine, or you'll drag it all over the place with the dipper. If you're pulling with the dipper, the grapple is pointed the wrong way to do any good. If you're pushing with the grapple, I'm hoping the BH is raised, centered, and PINNED in the transport position. If not, you're begging for disaster.

Your definition of "at the same time" is too narrow. For the purposes of this discussion if you have the backhoe connected on the back and the grapple on the front you are using the backhoe and grapplec "at the same time".

If the 3rd function valve is fed from the backhoe valve every time you close or open the grapple the backhoe valve is seeing the pressure in the grapple cylinders as back pressure on the outlet port. That can be as much as the relief pressure in the loader valve which is north of 2000 PSI.

The backhoe valve is designed for a maximum outlet pressure of 1/4 of that and when plumbed in that order you risk damage to the backhoe valve. The Kubota supplied warning sticker was provided for a reason. I would suggest heeding it. Apparently the dealer that did the install felt otherwise.

Dan

 

[Old_Paint]

Your definition of "at the same time" is too narrow. For the purposes of this discussion if you have the backhoe connected on the back and the grapple on the front you are using the backhoe and grapplec "at the same time".

If the 3rd function valve is fed from the backhoe valve every time you close or open the grapple the backhoe valve is seeing the pressure in the grapple cylinders as back pressure on the outlet port. That can be as much as the relief pressure in the loader valve which is north of 2000 PSI.

The backhoe valve is designed for a maximum outlet pressure of 1/4 of that and when plumbed in that order you risk damage to the backhoe valve. The Kubota supplied warning sticker was provided for a reason. I would suggest heeding it. Apparently the dealer that did the install felt otherwise.

Dan

Ok, maybe I'm getting a little closer to understanding what you're saying. Haven't seen or read the sticker, because I don't have the BH, despite my original intent when I bought my LX. I would ALWAYS heed the manufacturer's instructions for attachments because they're usually safety related and thinking about breaking a new and expensive tractor gives me hives.

I think I covered "on the tractor at the same time" versus simultaneous operation. There is a difference. I would think if I was worried that the order is wrong, and until it is corrected, I would probably bypass the hoe anytime I was using the FEL/Grapple. Looks pretty simple/quick to do, and seems the better alternative to having hydraulic fountains at the BH valve stand.

I guess my next question would be why a tractor dealer would possibly do the installation wrong, especially with manufacturer instructions. I can come up with exactly three reasons, both bad.

1. Ignorance
2. Apathy
3. Cutting cost corners (probably directly related to the first two reasons) with shorter hoses.

Don't get me wrong, I'm not arguing with you, just trying to educate myself about Kubota's designs and requirements without diagrams, as well as try to identify what is causing the restrictions and back-pressures that would make a difference in the order things are connected. Sometimes, I'm just nosey and want to understand someone's issue better so maybe I can avoid it. I.E., I'm enhancing what I already know SOME about. Not my first rodeo with hydraulics, but perhaps with Kubota hydraulics designs. I'm fully aware that I'm an electrical engineer, not a hydraulics engineer. But I figure I can understand it if someone's patient enough to teach me and make scribblies for me. This is another example of "If you want 5 ONLY ways to do something, just ask 5 engineers", which ALWAYS intrigues me. It lets me find out if others think like me, ergo, are they as crazy as me.

 

[TheOldHokie]

Ok, maybe I'm getting a little closer to understanding what you're saying. Haven't seen or read the sticker, because I don't have the BH, despite my original intent when I bought my LX. I would ALWAYS heed the manufacturer's instructions for attachments because they're usually safety related and thinking about breaking a new and expensive tractor gives me hives.

I think I covered "on the tractor at the same time" versus simultaneous operation. There is a difference. I would think if I was worried that the order is wrong, and until it is corrected, I would probably bypass the hoe anytime I was using the FEL/Grapple. Looks pretty simple/quick to do, and seems the better alternative to having hydraulic fountains at the BH valve stand.

I guess my next question would be why a tractor dealer would possibly do the installation wrong, especially with manufacturer instructions. I can come up with exactly three reasons, both bad.

1. Ignorance
2. Apathy
3. Cutting cost corners (probably directly related to the first two reasons) with shorter hoses.

Don't get me wrong, I'm not arguing with you, just trying to educate myself about Kubota's designs and requirements without diagrams, as well as try to identify what is causing the restrictions and back-pressures that would make a difference in the order things are connected. Sometimes, I'm just nosey and want to understand someone's issue better so maybe I can avoid it. I.E., I'm enhancing what I already know SOME about. Not my first rodeo with hydraulics, but perhaps with Kubota hydraulics designs. I'm fully aware that I'm an electrical engineer, not a hydraulics engineer. But I figure I can understand it if someone's patient enough to teach me and make scribblies for me. This is another example of "If you want 5 ONLY ways to do something, just ask 5 engineers", which ALWAYS intrigues me. It lets me find out if others think like me, ergo, are they as crazy as me.

This is pretty basic. Open center valves are typically limited in the amount of pressure allowed on the tank port. The number will vary from manufacturer to manufacturer but the neighborhood is 300-500 PSI. The catalog descriptions will give you the number. So the warning sticker on the backhoe makes perfect sense. The installation performed by the dealer who affixed that sticker does not.

The solenoid valves used for 3rd function are an exception. They can handle 2000-3000 PSI on the tank port which is why they are being used like this.

If it were me I would:

1. Immediately contact the dealer and ask for an explanation.
2. If the dealer could not offer an acceptable explanation and refuses to change the order I would do it myself.

Operating the grapple with the 3rd function on the downstream side of the backhoe is a crap shoot. If you take care not to deadhead the cylinders your odds of having a problem are pretty slim. If you forget and run the pressure up it might fail the first time it happens. A lot depends on the design of the backhoe valve. Lots of people with minimal understanding of hydraulics unwittingly install valves like this when adding remotes to tractors and run them for years with zero problems.

But if it does fail the dealer is going to be the one on the hook for the failure and the owner is going to be without a machine until it gets repaired.

Dan

 

[Sammy3700]

Thanks to all you’ll!! Everyone just saved me problems in the future I was in the process of plumbing in a 3rd function on one of my L3800hst tractors which is setup with a bh77. I have it first out of the loader power beyond and then routed to the back hoe so the Back hoe dumps in the factory return port.

 

[Old_Paint]

This is pretty basic. Open center valves are typically limited in the amount of pressure allowed on the tank port. The number will vary from manufacturer to manufacturer but the neighborhood is 300-500 PSI. The catalog descriptions will give you the number. So the warning sticker on the backhoe makes perfect sense. The installation performed by the dealer who affixed that sticker does not.

The solenoid valves used for 3rd function are an exception. They can handle 2000-3000 PSI on the tank port which is why they are being used like this.

If it were me I would:

1. Immediately contact the dealer and ask for an explanation.
2. If the dealer could not offer an acceptable explanation and refuses to change the order I would do it myself.

Operating the grapple with the 3rd function on the downstream side of the backhoe is a crap shoot. If you take care not to deadhead the cylinders your odds of having a problem are pretty slim. If you forget and run the pressure up it might fail the first time it happens. A lot depends on the design of the backhoe valve. Lots of people with minimal understanding of hydraulics unwittingly install valves like this when adding remotes to tractors and run them for years with zero problems.

But if it does fail the dealer is going to be the one on the hook for the failure and the owner is going to be without a machine until it gets repaired.

Dan

So, what we're saying, then, is that the grapple does not have a pass-through port, only a tank port, which is what is feeding the backhoe. Yeah, I can see where that would cause much problems. In my preference, any valve/valve body should have a tank port and a pass-through port (or power beyond, whatever you want to call it.)

I can't see the 3PH causing any problems if it is appropriately adjusted. There's a procedure for it, use it. I'm sure more than one person has had overheating of the oil, backhoe or not, because of a misadjusted 3PH lift motion. Going down, it's merely vent to tank, so no problemo. Right now, because I moved the lift links to the closest holes (because of my oversize tires), anything below 4 is useless on my 3PH lever gauge. What I would probably do if I had the BH77 is run the 3PH all the way down and leave it there. Besides that, IIRC, the lift is pretty low pressure too, and not likely to exceed the ratings of the BH valves.

I'd still be very wary of valves on a 2000-3000 PSI system that were rated for 500 PSI. I simply cannot fathom every component not being rated for the max pressure. Gonna have to keep that in mind from now on when I look at accessories and how to power them. Definitely considering some remotes for future projects/tools. If, however, the BH77 is equipped with a pressure relief on a valve manifold with a pass-through port and separate return to tank line, ok, I can buy into the lower pressure valves. Some of the valve rating is going to be a function of flow. Higher flow (less restriction) typically means lower pressure rating because the pressure drop is mitigated.

Thanks for the education, Dan. Looks like the BH77 is a completely different application of hydraulics than I am used to seeing, where EVERYTHING operates at 3000-4000 PSI on a common pressure header, but has a separate RTT port versus pass-through for downstream connections. If I get a BH77 for my SU at this point, it'll be me installing it, so this is good info. It would still be pretty nice to see a complete hydraulic schematic with everything on it, including remotes and 3F valves. That might make me just a little bit more un-stoopid.

 

[TheOldHokie]

So, what we're saying, then, is that the grapple does not have a pass-through port, only a tank port, which is what is feeding the backhoe. Yeah, I can see where that would cause much problems. In my preference, any valve/valve body should have a tank port and a pass-through port (or power beyond, whatever you want to call it.)

I can't see the 3PH causing any problems if it is appropriately adjusted. There's a procedure for it, use it. I'm sure more than one person has had overheating of the oil, backhoe or not, because of a misadjusted 3PH lift motion. Going down, it's merely vent to tank, so no problemo. Right now, because I moved the lift links to the closest holes (because of my oversize tires), anything below 4 is useless on my 3PH lever gauge. What I would probably do if I had the BH77 is run the 3PH all the way down and leave it there. Besides that, IIRC, the lift is pretty low pressure too, and not likely to exceed the ratings of the BH valves.

I'd still be very wary of valves on a 2000-3000 PSI system that were rated for 500 PSI. I simply cannot fathom every component not being rated for the max pressure. Gonna have to keep that in mind from now on when I look at accessories and how to power them. Definitely considering some remotes for future projects/tools. If, however, the BH77 is equipped with a pressure relief on a valve manifold with a pass-through port and separate return to tank line, ok, I can buy into the lower pressure valves. Some of the valve rating is going to be a function of flow. Higher flow (less restriction) typically means lower pressure rating because the pressure drop is mitigated.

Thanks for the education, Dan. Looks like the BH77 is a completely different application of hydraulics than I am used to seeing, where EVERYTHING operates at 3000-4000 PSI on a common pressure header, but has a separate RTT port versus pass-through for downstream connections. If I get a BH77 for my SU at this point, it'll be me installing it, so this is good info. It would still be pretty nice to see a complete hydraulic schematic with everything on it, including remotes and 3F valves. That might make me just a little bit more un-stoopid.

The grapple is not feeding the backhoe. That is the problem.

There is no need for a tank port to be rated at full system pressure.

I will draw you a schematic. High pressure in red, low pressure in blue. Both the backhoe and grapple are using the tank port for high pressure carryover. The grapple valve is rated for that - the backhoe valve is not. Move the grapple ahead of the backhoe and everything is OK because when the backhoe is mounted the 3pt is disabled.

Dan

 

[Henro]

The grapple is not feeding the backhoe. That is the problem.

There is no need for a tank port to be rated at full system pressure.

I will draw you a schematic. High pressure in red, low pressure in blue. Both the backhoe and grapple are using the tank port for high pressure carryover. The grapple valve is rated for that - the backhoe valve is not. Move the grapple ahead of the backhoe and everything is OK because when the backhoe is mounted the 3pt is disabled.

Dan

View attachment 71685

Dan,

I would’ve expected that the backhoe would have a power beyond outlet port that went to whatever was down stream, and a return to tank port. Your drawing surprises me, but I have no knowledge of the backhoe control valve in question.

let’s say the grapple was not on your drawing and the backhoe fed the three-point directly. Wouldn’t the situation at the backhoe T port be the same, if the three-point hitch was run up to the end of the stroke and held there dead headed?

 

[Henro]

Second Question, how is the 3PH disabled when the backhoe is mounted?

I clearly see what you are saying if the grapple valve is moved ahead of the backhoe control valve assembly, and the 3PH is eliminated from the circuit, so that the backhoe T port goes into the return to tank line.

3rd question, if the the 3PH is out of the picture when the backhoe is on, why do you show it in the drawing? Just trying to be sure I am not missing something.

Edit: Now I will go back and read the thread again. I was having difficulty following what was being discussed, kept thinking how a drawing would help…(Did go back. Discussion makes sense to me now…)

 

[Chanceywd]

Dan,

I would’ve expected that the backhoe would have a power beyond outlet port that went to whatever was down stream, and a return to tank port. Your drawing surprises me, but I have no knowledge of the backhoe control valve in question.

let’s say the grapple was not on your drawing and the backhoe fed the three-point directly. Wouldn’t the situation at the backhoe T port be the same, if the three-point hitch was run up to the end of the stroke and held there dead headed?

I think you are asking what I asked. While the explanations here make sense I still have don't quite get the 500 or so max number at the 3pt holding it and hitting end of stroke. Maybe it is internal design of the 3pt valve I am not aware of. I am OK with not getting it but glad to have read this discussion too.

Bill

 

[Old_Paint]

The grapple is not feeding the backhoe. That is the problem.

There is no need for a tank port to be rated at full system pressure.

I will draw you a schematic. High pressure in red, low pressure in blue. Both the backhoe and grapple are using the tank port for high pressure carryover. The grapple valve is rated for that - the backhoe valve is not. Move the grapple ahead of the backhoe and everything is OK because when the backhoe is mounted the 3pt is disabled.

Dan

View attachment 71685

Now I see what you're talking about, and it was EXACTLY the problem I was envisioning from the descriptions. Without some kind of pressure reducer, the only way to protect the BH is to make sure it's the last thing next to the 3PH. I'm still a little put out that 500 PSI valves are used on something that has a 2500 PSI supply. It ain't like they didn't know, nor is it really designed to fit any other brand of tractor that might not have that much pressure. Makes no sense at all, really. Why not size the hydraulics for the max system pressure?

 

[TheOldHokie]

I think you are asking what I asked. While the explanations here make sense I still have don't quite get the 500 or so max number at the 3pt holding it and hitting end of stroke. Maybe it is internal design of the 3pt valve I am not aware of. I am OK with not getting it but glad to have read this discussion too.

Bill

This is really not all that complicated. Please don't be offended by the emphasis but its crucial to understanding how the 3pt on a tractor with open center hydraulics works:

A properly designed and adjusted open center 3pt lift unloads the pump at end of stroke and does not continue to call for lift.

This is fundamentally important. It does that to avoid damaging the pump and other components by subjecting them to high pressure for extended periods of time.

So you ask - "How does it do that? ".

The 3pt control lever is not directly coupled to the spool in the valve. The spool is typically shifted by a piloted hydraulic shuttle that moves in response to changes in the lever AND lift arm position. This is called position control - you set the lever to the height you want the lift positioned and the feedback linkages call for lift only until the the arms reach that setting. If the cylinder leaks off a bit and the height drops the the feedback loop automatically calls for lift to restore the position. No operator action is required and the lever does not move - but the spool inside the valve does. If you move the lever lower or higher the feedback loop sees that change in lever position and the shuttle shifts the spool in or out as needed to adjust the position of the lift accordingly. Draft control and closed center systems are a different animal so we will leave that for another day. Most of these CUTS are simple open center systems with position control.

With or without position/draft control, when properly designed and adjusted the 3pt system should always automatically return the spool to neutral at top of lift. This is necessary to avoid dead heading the pump against the relief valve (full system pressure) for extended periods of time. That would drastically shorten system life.

The details vary by make or model but every tractor I have ever owned or operated operates on those general principles. I just happened to have the lever guide plate on my new L3901 off yesterday and I did some experimenting. Here is how it behaves:

1. With the plate off I can move the lever to a full up position where the pump is deadheaded against one of the pressure relief valves in the system. I don't have to hold it there - it will stay on its own. I can tell that the pump is deadheaded because if the loader is raised it will not lower. The path to tank for that spool is through the power beyond port on the loader valve and it is sitting at full system pressure. The bucket spool works fine because it employs a regen circuit and does not need a path to tank. If I move the 3pt lever just a tiny bit lower the pump is unloaded and the loader will operate correctly.
2. With the lever guide plate installed there is a non-adjustable stop at the top of the position control lever slot that limits the travel of the lever. That stop makes it impossible for me to raise the lever to the point the pump is deadheaded. This is by design!!! It prevents a numb-nutz operator like me from damaging the pump or other system component.

Go play with your tractor and see how it behaves. If you can deadhead the pump with the 3pt lever something strange is going on.

Dan

 

[TheOldHokie]

I'm still a little put out that 500 PSI valves are used on something that has a 2500 PSI supply. It ain't like they didn't know, nor is it really designed to fit any other brand of tractor that might not have that much pressure. Makes no sense at all, really. Why not size the hydraulics for the max system pressure?

It makes perfect sense and its an industry standard design. These valves are not designed for high pressure carry over use. They are for use in a system where they are the last or only valve in the circuit. If you use one of these types of valves to supply pressure to a down stream device you the end user are screwing up. You could make a case that Kubota has a history of doing just that with their back hoes.

If you are going to feed a down stream device you need to use a valve with high pressure carry over. Many of these commodity open center valves are convertible. They have two "tank" ports. To convert them to high pressure carry over you install a sleeve in one of those tank ports. That connects that port to the center core for carrying high pressures and isolates it from the low pressure tank core. There are a lot of other issues associated with high pressure carry over - tank back pressure is just one and probably the least concerning. The use of these open center solenoid valves for third function is another questionable design.

Dan

 

[Chanceywd]

It makes perfect sense and its an industry standard design. These valves are not designed for high pressure carry over use. They are for use in a system where they are the last or only valve in the circuit. If you use one of these types of valves to supply pressure to a down stream device you the end user are screwing up. You could make a case that Kubota has a history of doing just that with their back hoes.

If you are going to feed a down stream device you need to use a valve with high pressure carry over. Many of these commodity open center valves are convertible. They have two "tank" ports. To convert them to high pressure carry over you install a sleeve in one of those tank ports. That connects that port to the center core for carrying high pressures and isolates it from the low pressure tank core. There are a lot of other issues associated with high pressure carry over - tank back pressure is just one and probably the least concerning. The use of these open center solenoid valves for third function is another questionable design.

Dan

Hey Dan, the light bulb in my head just lit up with these last explanations. I remember years ago rebuilding the pump in my 8N and adjusting that with it's linkage. Then when I added my own front pump and loader valve to use with my plow I dealt with the that valve and the sleeve issue.
So thank you for taking the time and sharing. I will look at the kubota a little closer.

Bill

 

[TheOldHokie]

Hey Dan, the light bulb in my head just lit up with these last explanations. I remember years ago rebuilding the pump in my 8N and adjusting that with it's linkage. Then when I added my own front pump and loader valve to use with my plow I dealt with the that valve and the sleeve issue.
So thank you for taking the time and sharing. I will look at the kubota a little closer.

Bill

Glad the light os on.

The grand daddy of them all 9N lift and pump is a crazy design but even it shuts off at end of stroke assuming the Rube Goldberg inkage is working. You may have run across people talking about problems with the "unloader" valve on the NAA. That's the shuttle I am talking about. Another iffy Ford design and chronic complaint.

Dan