Thumb Mini Excavator thumb

[tractorcrazy]

I'm going to add a thumb to my mini Excavator I'm going to make it out of steel I have laying around. My question is while using it I assume you keep it up out if the way when not in use. What would happen if it was in the middle of its stroke and I curl the bucket into it by accident would it bend the cylinder. Thanks Rick

 

[BertZegers]

You rely on the relief valve to protect the cylinder. The same as when you curl the bucket to break loose a tree stump or something.

 

[tractorcrazy]

Thanks bert I wasn't sure how that worked

 

[ovrszd]

Someone correct me if I'm wrong but I believe a factory thumb system has a bypass built into the thumb hydraulics to protect the cylinder? Bucket would simply push it out of the way?

Read an extensive discussion about this here on TBN but I can't find it now. Hopefully someone with personal knowledge will chime in.

 

[4570Man]

Someone correct me if I'm wrong but I believe a factory thumb system has a bypass built into the thumb hydraulics to protect the cylinder? Bucket would simply push it out of the way?

Read an extensive discussion about this here on TBN but I can't find it now. Hopefully someone with personal knowledge will chime in.

That’s how there’re supposed to work. Unlike regular valves the thumb is relived all the time and the bucket can push it backwards.

 

[ovrszd]

That’s how there’re supposed to work. Unlike regular valves the thumb is relived all the time and the bucket can push it backwards.

I think something like this would be required in the case of a home built thumb. Otherwise you would risk destroying the thumb cylinder.

 

[ptsg]

Does the excavator already have the lines for the thumb? I would check on the valve block, if it's equipped with relief valves on the work ports of the valve. Most excavators do but it's still something to check out.

On my homemade backhoe, I simply added a relief valve on the extend side of the cylinder to prevent issues. Actually, first test I did with the thumb, didn't have the relief valve installed yet and the thing the blew the piston seals.

 

[ovrszd]

On my homemade backhoe, I simply added a relief valve on the extend side of the cylinder to prevent issues. Actually, first test I did with the thumb, didn't have the relief valve installed yet and the thing the blew the piston seals.

Yeah, I think that's similar to what he'll need.

Can't just depend on the excavator's relief valves.

This stress would be similar to back dragging with your FEL bucket curled forward. Common to see threads on here about bent curl cylinders. The force on the bucket is greater than the strength of the cylinder rod.

 

[downsizingnow48]

The valve I used to make my hyd thumb has reliefs on both work ports. Need both for when the thumb is pushing or being pushed.

 

[ovrszd]

The valve I used to make my hyd thumb has reliefs on both work ports. Need both for when the thumb is pushing or being pushed.

There ya go. Good stuff Pat!!!