Backhoe Thumb Hydraulic Options

[dfkrug]

I guess to "stow" the thumb the cylinders are left in parallel and spread until the thumb is in the stowed
position and then the switch is thrown into "curl only"?

Ya beat me to posting the link. You may have found the other discussions about this, too.

When in grapple mode (both cyls connected in parallel) and the dipper is extended out past
perpendicular, operating the bkt dump lever will pressurize both cyls, but only the thumb
will move cuz gravity works for it, and against the bkt. I turn the switch off as soon as the
thumb is 180-deg to the dipper, and there it stays.

I did numerous experiments, mockups, and calcs to come up with a design that works
very well for over 5y of moving hundreds of rocks and trees. WITHOUT using additional
work-port RVs. In that time, I have replaced one damaged hose, and added a few welds
to cracks in my 12" bkt. One day I might weld some hose protection to the dipper.

At the risk of repeating what I put in the above thread, part of making this work is
building a thumb that withstands the reaction forces of the bkt. Obviously the cyls
should be the same size, but I also used 4500psi wp hoses, and fabbed a welded cyl that
can take 3500psi. Oh, and 1" pins.

 

[dfkrug]

The solenoid valve used by the above person, is still not free from damage, because if he
removes the 12 v, the force is against the thumb and the solenoid valve, and if it does not have a relief, either the
cyl or the valve could be damaged.

Could be damaged? Sure, but only if not properly designed. I am not asking anyone to trust my
design, but it is hard to refute my experience using this design in the field without problems.

And, as pointed out above, the OEM hyd thumbs do not have any problems overpowering their
associated buckets. And, I will bet that they have not resorted to work-port RVs. Even if they
do, I have never seen nor heard of a factory thumb/bkt combo where one pushes the other back.

My first hyd thumb use was on a Takeuchi mini-X, and it sure did not.

 

[avc8130]

Could be damaged? Sure, but only if not properly designed. I am not asking anyone to trust my
design, but it is hard to refute my experience using this design in the field without problems.

And, as pointed out above, the OEM hyd thumbs do not have any problems overpowering their
associated buckets. And, I will bet that they have not resorted to work-port RVs. Even if they
do, I have never seen nor heard of a factory thumb/bkt combo where one pushes the other back.

My first hyd thumb use was on a Takeuchi mini-X, and it sure did not.

The more I think about it, wouldn't a design where one could push the other back be utterly useless? If the bucket could overcome the thumb before hydraulic relief cut off the flow to the curl cylinder, wouldn't every "pinch" wind up with a collapsed and useless thumb?

ac

 

[MtnViewRanch]

The more I think about it, wouldn't a design where one could push the other back be utterly useless? If the bucket could overcome the thumb before hydraulic relief cut off the flow to the curl cylinder, wouldn't every "pinch" wind up with a collapsed and useless thumb?

ac

You are assuming that the thumb just gives way to be useless. If it takes 6000 pounds of pressure to move it, you can hold pretty darn good with that much pressure before it moves.

 

[avc8130]

You are assuming that the thumb just gives way to be useless. If it takes 6000 pounds of pressure to move it, you can hold pretty darn good with that much pressure before it moves.

Yeah, I guess I am forgetting about the mechanical leverage.

I need to sit down and fully work through the thumb setup. I need to figure out exactly how I want to do it.

Is it possible to just add a valve to the factory backhoe control stack like Kubota does, or is Kubota's valve proprietary?

ac

 

[J_J]

Just go to Kubota dealer and get a spool stack of your choice, or find out the manufacturer of your valve and add to it.

 

[avc8130]

Just go to Kubota dealer and get a spool stack of your choice, or find out the manufacturer of your valve and add to it.

I checked the Kubota part number...the valve ALONE is $560 through them.

How can I ID who makes the valves for Kubota?

ac

 

[J_J]

Do you need the complete valve, or a couple of spools to add to the current valve?

 

[Arc weld]

If you make a make your own thumb, use a higher quality cylinder than the ones at the farm store. When using the thumb, you don't keep pushing the lever trying to get more force. The worst that should happen is the other cylinder retracts a bit. You could possible blow cylinder seals with a lower end cylinder that just uses O-rings for seals. If a hose blows it's not because one is pushing against the other and causing more pressure. Hoses sometimes just blow. There's thousands of thumbs out out there without any problems. With a good valve and some experience you can feel how hard the cylinder is pushing the same way you can tell how hard the bucket is digging.

 

[Coyote machine]

Coyote machine,

What happened to you is what I was trying to say.

I would think a relief valve on the base end of the cyl and running the relief port to tank would prevent the excess pressure.

Just set it to a lower pressure than the BH valve or the tractor valve.

With no relief on the cyl, anything pushing on the thumb cyl will probably generate enough pressure to damage the cyl or hoses.

If you do the math, you can come close to figuring out the correct size cyl to use to oppose the curl cyl setup.

The solenoid valve used by the above person, is still not free from damage, because if he removes the 12 v, the force is against the thumb and the solenoid valve, and if it does not have a relief, either the cyl or the valve could be damaged.

Thanks, JJ. You are the hydraulics MAN!:thumbsup:
Spoke to my original thumb dealer and we're working on a different cylinder/thumb setup where a bigger cylinder can balance out against the bucket- I owe it all to this thread- thanks to the OP too, hope you get/make what you need

CM out

 

[avc8130]

Do you need the complete valve, or a couple of spools to add to the current valve?

I'm not sure on the terminology. Kubot uses a stack of valves to control the backhoe. For the factory thumb option, they add a valve to the stack. This "addition" is $560 without the hoses, fittings, foot control, etc.



That last piece in the stack before the end cap is the thumb "valve".

ac

 

[J_J]

You should be able to get replacement spools for that stacked valve.

You may not be able to add to the stack assembly and make it fit in the allowed space.

You can add a 3rd function valve to move the thumb, or if the BH valve has PB, just add another foot control valve.


This is some data from a thumb manufacturer.

CautionCautioCautionn

HYDRAULIC PRESSURE ON THUMB CYLINDER SHOULD NOT
EXCEED 2000 PSI. IT IS ESSENTIAL TO PERFORM TESTS TO
ENSURE THAT THE BUCKET AND ATTACHMENTS ALWAYS
OVERPOWER THE THUMB. FAILURE TO DO SO WILL CAUSE
DAMAGE TO THUMB, PINS, CYLINDERS, BRACKETS AND STICK.
Valve

 

[avc8130]

You should be able to get replacement spools for that stacked valve.

You may not be able to add to the stack assembly and make it fit in the allowed space.

You can add a 3rd function valve to move the thumb, or if the BH valve has PB, just add another foot control valve.


This is some data from a thumb manufacturer.

CautionCautioCautionn

HYDRAULIC PRESSURE ON THUMB CYLINDER SHOULD NOT
EXCEED 2000 PSI. IT IS ESSENTIAL TO PERFORM TESTS TO
ENSURE THAT THE BUCKET AND ATTACHMENTS ALWAYS
OVERPOWER THE THUMB. FAILURE TO DO SO WILL CAUSE
DAMAGE TO THUMB, PINS, CYLINDERS, BRACKETS AND STICK.
Valve

There is plenty of space for the thumb addition on the stack. Kubota designs it perfectly, even including the extra threaded mount bosses and everything. That last valve that you can see in the picture that is operated by the foot pedal is NOT currently installed on my machine. That is what I would need to add.

We really need a FAQ in the hydraulic section, at least to establish what all of these terms mean so we can talk with the same vocabulary.

ac

 

[J_J]

Someone has done some of the abbreviations explanations but not all in one spot.

Just what something means.

Sometimes it is just easier to use short titles.

 

[avc8130]

Someone has done some of the abbreviations explanations but not all in one spot.

Just what something means.

Sometimes it is just easier to use short titles.

Right, so if I wanted to add the factory style setup...what do I need?

Here is the parts diagram from Kubota. You can see how they just add a valve/spool (what is the proper term?) to the stack (proper term?).



How can I figure out if there is a commercial way to get that component without paying Kubota's $560?

ac

 

[J_J]

Is there a name or number on the valve anywhere?

Have you checked what one spool would cost, and the longer bolts required?

Did you compare the stacks to Prince or any other manufacturer?

What is included in the $560 price?

You might visit the hyd shop in the dealership and inquire about a used stack.

Sometimes the guys in the back will help more than the service manager.

 

[avc8130]

Is there a name or number on the vale anywhere?

Have you checked what one spool would cost, and the longer bolts required?

Did you compare the stacks to Prince or any other manufacturer?

What is included in the $560 price?

You might visit the hyd shop in the dealership and inquire about a used stack.

Sometimes the guys in the back will help more than the service manager.

I'll have to take a really close look at the stack when I get home.

$564 buys "010" from that picture.

ac

 

[J_J]

That price is tota BS.

Here is a stack valve from this vender and each stack is aobut $80

Sectional Control Valves

Here is the stack prices from Surplus for their stacked valve.

Spring center with port relief is only $128.

Surplus Center - 7 SPOOL SV VALVE OPEN CENTER W/POWER BEYOND

If you have to stick with your valve, then I would go 3rd function or diverter valve.

You could even install a log slitter valve on the thumb and have it retract to rest automatically using detent.

There are many ways to do this.

Some people want to play with the thumb, and others just want to place/set the thumb using a cyl and leave it stationary for the duration of the work.

 

[J_J]

This BH valve with 6 spools cost about $480, and you can add another $80 valve using the PB port.

Directional Control Valves 22 Series | Type 4-way 3 pos. tandem center 6 SPL W/2JOYSTICKS 220-951

 

[avc8130]

That price is tota BS.

If you have to stick with your valve, then I would go 3rd function or diverter valve.

You could even install a log slitter valve on the thumb and have it retract to rest automatically using detent.

There are many ways to do this.

Some people want to play with the thumb, and others just want to place/set the thumb using a cyl and leave it stationary for the duration of the work.

Exactly my point. Kubota's price is insane. That is why I was hoping to find a valve that would be compatible with the stack to add.

I guess it is unknown who makes the valves for Kubota?

As you know, I started this post thinking about a diverter. We have gone in so many circles I'm dizzy now. LOL

ac