BH77 Hydraulic Concerns

[NewOrangeMan]

Just got my LX2610HST back from the dealer where they installed the BH77 backhoe. I noticed the re-piped the 3rd function hydraulic hoses to be in series after the backhoe. I also noticed a new safety warning label saying not to install anything after the backhoe that could cause high back pressure on the Backhoe valves as seal damage could occur. My question is if the backhoe is not in use while let's say a grapple is used on the front, would the line pressure on the backside of the backhoe valves (return line out) damage them when they were not in use?

 

[TheOldHokie]

Just got my LX2610HST back from the dealer where they installed the BH77 backhoe. I noticed the re-piped the 3rd function hydraulic hoses to be in series after the backhoe. I also noticed a new safety warning label saying not to install anything after the backhoe that could cause high back pressure on the Backhoe valves as seal damage could occur. My question is if the backhoe is not in use while let's say a grapple is used on the front, would the line pressure on the backside of the backhoe valves (return line out) damage them when they were not in use?

First question: Is your backhoe hydraulic hookup a two or three hose connection? The parts manual shows it as two.

If the hookup is two hoses AND the 3rd function valve is installed after the backhoe valve the tank outlet on the backhoe valve will see the same pressure as the 3rd function cylinders. That could easily be 2000 PSI. I can't speak authoritatively to the potential for damage but that seems to violate the cautions on the warning label.

Dan

 

[NewOrangeMan]

That is my concern, the BH is a two hose hookup and the dealer plumbed the 3rd function valve in series on the return line from the BH. So if I have the grapple on the front and use it, I presume the full system pressure would be going through the BH valve assemble which I don't think would hurt it as long as it is not in use also, but I just don't know.

 

[Fedup]

I would agree with Dan. The way it's described, the valve stack would need to be configured for "power beyond" with a third line for sump return. Without that the low pressure passages in the valve stack (mainly the valve spool seals) would be subjected to whatever pressure builds in the functions downstream. Most valves are not built for that.

However if the third function valve is mounted ahead of the valve stack, it too must be capable of accepting pressure on its back side as well. If it's a solenoid valve, it probably will be.

 

[TheOldHokie]

That is my concern, the BH is a two hose hookup and the dealer plumbed the 3rd function valve in series on the return line from the BH. So if I have the grapple on the front and use it, I presume the full system pressure would be going through the BH valve assemble which I don't think would hurt it as long as it is not in use also, but I just don't know.

If I were you I would be asking this question of the dealer that installed the hoe. They put the warning label on so one would think they read it

I am in agreement with Fedup - spool stem seals are the primary concern but I have seen valves run that way with zero problems. I also don't think it matters if the BH valve is in use or not.

Of course those valves were not Kubota backhoe valves installed by the dealer and still under warranty......

Dan

 

[leveraddict]

Plain and simple I would ask the dealer.

 

[Jchonline]

You could ask them show you the configuration/setup documentation from Kubota (if one exists).

 

[kubotafreak]

I would suggest taking the backhoe out of circuit when using front 3rd function. You cant use both at the same time anyway. As there are so many configurations of 3rd functions out there, with some being appropriate, and others not. The only sure way is to remove the backhoe from the equation. The seals that will blow are the ones atop the BH valve body. The thin retaining plate will get forced up and the seal pushed out. Somewhat easy to remedy, but damage none the less. Some third function valves like others have said are self regulated(relief) and have tank return ports. Most do not and can cause pressure spikes in feed lines at shut off. You will know, because the backhoe will twitch every time the solenoid is actuated.

The third function should be ran first after the loader valve, on the PB circuit. The PB from the third function should feed the input of the backhoe. If not then your concerns are valid. It is ok for the three point to be fed off the backhoe (pb) return.

loader valve>third function>backhoe>threepoint

 

[Chanceywd]

Isn't the the 3 point hitch the last valve in the power beyond loop? Would lowering and raising this cause the same kind of problems with the backhoe valve if it were to be a problem when the backhoe is mounted. I thought the only difference between the FEL, 3rd function and the backhoe valves in the power beyond circuit was the FEL has a tank return. I must be missing something in it making a difference the order of the 3rd function or the backhoe based on the power beyond function as long as the flow direction is right.
Just when it thought I had a grasp of mine I am confused.

Bill

 

[TheOldHokie]

Isn't the the 3 point hitch the last valve in the power beyond loop? Would lowering and raising this cause the same kind of problems with the backhoe valve if it were to be a problem when the backhoe is mounted. I thought the only difference between the FEL, 3rd function and the backhoe valves in the power beyond circuit was the FEL has a tank return. I must be missing something in it making a difference the order of the 3rd function or the backhoe based on the power beyond function as long as the flow direction is right.
Just when it thought I had a grasp of mine I am confused.

Bill

Yes and yes.

The typical 3rd function valve is a solenoid operated valve designed to handle well in excess of 2000 PSI on the outlet port. The backhoe valve is a vanilla open center design and outlet pressure on it is typically limited to less than 500 PSI.

The purpose of a power beyond (high pressure carry over) port in a directional control valve is to separate the tank return function from the down stream pressure function. All return oil from the work circuits (cylinders/motors) goes to the tank port and only pump pressure goes to the power beyond port. A proper design would use a backhoe valve with a PB/HPCO circuit not a vanilla open center where tank is being used to power a downstream device (e.g. 3pt). In practice this is not an issue with sub-frame mounted hoes like the BH77 because the 3pt is not functional when the hoe is mounted. But the 3rd function is so it should be installed ahead of the backhoe. Kubota has corrected this potential for problems on the newer model hoes. They have a valve with HPCO and 3 lines connected to the tractor - pressure in from the tractor, HPCO back to the tractor, and a direct tank return.

Dan

 

[TheOldHokie]

I would suggest taking the backhoe out of circuit when using front 3rd function. You cant use both at the same time anyway.

If I am clearing brush and stumps with a grapple on the loader and the backhoe on the back I am using them both at the same time. This would be a pretty common type of usage and certainly one that the machine should accommodate.

Dan

 

[PoTreeBoy]

Isn't the the 3 point hitch the last valve in the power beyond loop? Would lowering and raising this cause the same kind of problems with the backhoe valve if it were to be a problem when the backhoe is mounted. I thought the only difference between the FEL, 3rd function and the backhoe valves in the power beyond circuit was the FEL has a tank return. I must be missing something in it making a difference the order of the 3rd function or the backhoe based on the power beyond function as long as the flow direction is right.
Just when it thought I had a grasp of mine I am confused.

Bill

Yep and yep. The L35 has a valve to bypass the 3PH to tank when the backhoe is installed, rendering the 3PH inop. The owner's manual carries a warning to switch the valve to prevent damage to the valve. (BT900 backhoe doesn't have power beyond).

 

[Chanceywd]

Yes and yes.

The typical 3rd function valve is a solenoid operated valve designed to handle well in excess of 2000 PSI on the outlet port. The backhoe valve is a vanilla open center design and outlet pressure on it is typically limited to less than 500 PSI.

The purpose of a power beyond (high pressure carry over) port in a directional control valve is to separate the tank return function from the down stream pressure function. All return oil from the work circuits (cylinders/motors) goes to the tank port and only pump pressure goes to the power beyond port. A proper design would use a backhoe valve with a PB/HPCO circuit not a vanilla open center where tank is being used to power a downstream device (e.g. 3pt). In practice this is not an issue with sub-frame mounted hoes like the BH77 because the 3pt is not functional when the hoe is mounted. But the 3rd function is so it should be installed ahead of the backhoe. Kubota has corrected this potential for problems on the newer model hoes. They have a valve with HPCO and 3 lines connected to the tractor - pressure in from the tractor, HPCO back to the tractor, and a direct tank return.

Dan

I guess what I am trying to understand is when my BH77 is on the 3pt is all the way up. If the adjustment of that limit on the back left is off by a few threads doesn't this pressurize the whole power beyond circuit and find relief with the FEL valve? I thought I had seen similar problems here, Maybe I didn't understand them right where if the 3pt is out of adjustment loader didn't have any power. Or is it a separate relief at the 3pt. I still wonder if there is times the 3pt could affect the power beyond circuit even with the BH77 on.

Thank you for your patience if don't quite grasp this right.
Bill

 

[TheOldHokie]

I guess what I am trying to understand is when my BH77 is on the 3pt is all the way up. If the adjustment of that limit on the back left is off by a few threads doesn't this pressurize the whole power beyond circuit and find relief with the FEL valve? I thought I had seen similar problems here, Maybe I didn't understand them right where if the 3pt is out of adjustment loader didn't have any power. Or is it a separate relief at the 3pt. I still wonder if there is times the 3pt could affect the power beyond circuit even with the BH77 on.

Thank you for your patience if don't quite grasp this right.
Bill

I dont know the specifics of the 3pt on your tractor but in general the only time there is pressure on the inlet to the 3pt valve is when you are lifting or lowering a load. When the spool is in neutral the inlet is connected to tank just like any other valve.

Dan

 

[kubotafreak]

Isn't the the 3 point hitch the last valve in the power beyond loop? Would lowering and raising this cause the same kind of problems with the backhoe valve if it were to be a problem when the backhoe is mounted. I thought the only difference between the FEL, 3rd function and the backhoe valves in the power beyond circuit was the FEL has a tank return. I must be missing something in it making a difference the order of the 3rd function or the backhoe based on the power beyond function as long as the flow direction is right.
Just when it thought I had a grasp of mine I am confused.

Bill

It does, but with the backhoe in place, there is little resistance on the three point lift cylinder. So little pressure to affect the backhoe valve body. I have moved the three point lever with the BH mounted and there has been no ill effects. If you were able to mount a 1400lb brush hog with the backhoe connected it would be a different story.

 

[kubotafreak]

If I am clearing brush and stumps with a grapple on the loader and the backhoe on the back I am using them both at the same time. This would be a pretty common type of usage and certainly one that the machine should accommodate.

Dan

You must be more nimble than me. On my rig it is enough of a battle to re-seat to drive the tractor forward to move when digging.(cab)

 

[Chanceywd]

I dont know the specifics of the 3pt on your tractor but in general the only time there is pressure on the inlet to the 3pt valve is when you are lifting or lowering a load. When the spool is in neutral the inlet is connected to tank just like any other valve.

Dan

That is where I guess my confusion was in the 3 pt, if there is anyway, if even by accident if the control lever was raised would that not put back pressure on the bh77 valve and cause damage such as was describe in the OP questions? I realize it wouldn't be loaded heavily.

Bill

 

[TheOldHokie]

That is where I guess my confusion was in the 3 pt, if there is anyway, if even by accident if the control lever was raised would that not put back pressure on the bh77 valve and cause damage such as was describe in the OP questions? I realize it wouldn't be loaded heavily.

Bill

No. The pressure needed to raise or lower an unloaded 3pt is well under the max allowed on the hoes outlet port. You are looking at just acfew hundred pounds of back pressure. Like I said earlier most valves are rated for something around 500 PSI max back pressure.

Dan

 

[Chanceywd]

No. The pressure needed to raise or lower an unloaded 3pt is well under the max allowed on the hoes outlet port. You are looking at just acfew hundred pounds of back pressure. Like I said earlier most valves are rated for something around 500 PSI max back pressure.

Dan

Thanks, Dan

 

[PoTreeBoy]

That is where I guess my confusion was in the 3 pt, if there is anyway, if even by accident if the control lever was raised would that not put back pressure on the bh77 valve and cause damage such as was describe in the OP questions? I realize it wouldn't be loaded heavily.

Bill

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 .