Backhoe Thumb Hydraulic Options

[avc8130]

I'm looking at my L45 and I would really "like" a thumb. Of course the Kubota kit is $1k+ for the valve part and $1500+ for the actual thumb. I want to focus on the valve side for now as I am pretty sure I can get the thumb side covered with some steel and a plasma cutter.

Kubota adds to the backhoe spool stack and uses a foot pedal to operate the additional valve. That seems "cool", but I would have to fabricate the whole pedal and linkage assembly.

I've been thinking about using a diverter valve. I could tap into one of the other functions on the hoe to control the thumb while still using my hands on the controls.

Anyone done this? Any fatal flaw to my idea?

ac

 

[J_J]

No, just get this valve and use one of the outrigger circuits . Add a switch and make the grapple the default mode.

Surplus Center - 12 VDC 13.2 GPM SAE 8 DOUBLE SELECTOR VALVE

http://www.ebay.com/itm/18-HEAVY-DU...avy_Equipment_Attachments&hash=item20d6ce1740

 

[avc8130]

No, just get this valve and use one of the outrigger circuits . Add a switch and make the grapple the default mode.

Surplus Center - 12 VDC 13.2 GPM SAE 8 DOUBLE SELECTOR VALVE

18" Heavy Duty Thumb for Backhoe Mini Excavator | eBay

Do you think the outrigger is the "right" place to borrow the function from? I was thinking one of the functions on the actual control sticks so I wouldn't have to move my hands. Just hold a button on the stick.

I'm not scared of the thumb portion. My hoe already has the cylinder mount on the arm and I will figure out the rest.

ac

 

[J_J]

You can put the selector on any spool in the valve. I just selected a lever that was not used that much.

If you did a 3rd function on the thumb, you could put the switch on any lever, and put a toggle fwitch for grapple extend or retract..

 

[avc8130]

You can put the selector on any spool in the valve. I just selected a lever that was not used that much.

If you did a 3rd function on the thumb, you could put the switch on any lever, and put a toggle fwitch for grapple extend or retract..

You've sold me on the ability to "feather" things now so I think I will do a diverter and think long and hard about which function to piggy back off of.

ac

 

[J_J]

You might keep this in mind about the cyl size.

Depending on the cyl size and mechanical advantage, one of the two cyl, the one on the bucket or the grapple cyl, will have more power than the other and cause the other cyl to compress and cause some damage.

An example might be a 10 ton cyl pushing against an 5 ton cyl, the 5 ton cyl will give on any pressure that will develop power above 5 ton. You might consider a relief valve across the cyl or maybe your BH has work port reliefs which would be a good thing. .

 

[avc8130]

You might keep this in mind about the cyl size.

Depending on the cyl size and mechanical advantage, one of the two cyl, the one on the bucket or the grapple cyl, will have more power than the other and cause the other cyl to compress and cause some damage.

An example might be a 10 ton cyl pushing against an 5 ton cyl, the 5 ton cyl will give on any pressure that will develop power above 5 ton. You might consider a relief valve across the cyl or maybe your BH has work port reliefs which would be a good thing. .

Yes, I definitely need to look into that. The thumb definitely needs to stop when it pushes against the curl and the fold back when the curl pushes against it.

ac

 

[MtnViewRanch]

Yes, I definitely need to look into that. The thumb definitely needs to stop when it pushes against the curl and the fold back when the curl pushes against it.

ac

The simple way to deal with this is to just get a smaller diameter cylinder for the thumb. Then it will never over power the curl cylinder.

 

[J_J]

That will not help as the larger cyl will usually develop more pressure than a smaller cyl. In order to be even close to equal, the cyl should be the same size.

Someone would have to work out the geometry to make them equal, so the next option is to put a relief valve across the thumb cyl, so it will relieve if the curl cyl over rides the thumb cyl.

In some cases, a locked down cyl would be better so the bucket could push against a solid bar.

There was one poster awhile back that said he could see the thumb cyl being compressed by the bucket, and it finally blew a hose.

If the BH has work port reliefs, the spool using the thumb should be adjusted to relieve before the curl cyl does.

 

[MtnViewRanch]

Why does it have to be equal? If the weak unit puts 6000lbs of pressure (which is plenty) against the curl cylinder that has 14000 lbs, unless the grapple cylinder has a huge leverage advantage what difference would it make? I will agree that the best situation seems like the grapple would have it's own relief.