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