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!!!

 

[BertZegers]

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.

I think you need only one. Click on the picture to enlarge.


The parts added for the thumb are shown in the red circle. In the third circuit are the Quick Connects for the log splitter.

If the pressure comes from the pump (pushing), then there is the main and/or bucket relief valve plus the thumb relief valve. If the pressure comes from the bucket pushing the thumb ( being pushed), the thumb relief valve will act. The thumb relief valve is adjusted to a lower pressure than the main relief valve, but high enough to hold the load.

Without the added relief valve you rely on the main and/or bucket relief valve only.

Here is how I have the relief valve plumbed in.

 

[ptsg]

I think you need only one. Click on the picture to enlarge.

View attachment 637949
The parts added for the thumb are shown in the red circle. In the third circuit are the Quick Connects for the log splitter.

If the pressure comes from the pump (pushing), then there is the main relief valve plus the thumb relief valve. If the pressure comes from the bucket pushing the thumb ( being pushed), the thumb relief valve will act. The thumb relief valve is adjusted to a lower pressure than the main relief valve, but high enough to hold the load.

Here is how I have the relief valve plumbed in.
View attachment 637950

Doesn't your KX41 have Work port relief valves on the thumb circuit already?

 

[BertZegers]

Doesn't your KX41 have Work port relief valves on the thumb circuit already?

Good question! I have never checked. The other reason for me to put this adjustable relief valve in is that I want the pressure on the bushings to be as low as possible. Bushings are very expensive!

I have used the "hammer port" for the thumb. The "hammer port" is also usable for a thumb by taking out the return hose and put a plug in. I basically put the thumb relief valve in the plug hole and used the return hose on the pressure relief valve. ( As the picture in my previous reply shows )

 

[tractorcrazy]

Yes it is already plumbed I just have to connect cylinder hose up to the existing quick coupler on the boom

 

[mike48130]

What model mini do you have? I just looked at my Bobcat 322 service manual and they have the port relief valves listed for the boom, bucket and arm cylinders, but not for the aux ports.

I've been looking at the weld on ones out there, and not sure if I want to build or make. But I think you need something on the cylinder to protect it.

 

[BertZegers]

Doesn't your KX41 have Work port relief valves on the thumb circuit already?

I looked, and all circuits have dedicated relief valves, except the "hammer/auxiliary" port, that is now used for the thumb.

 

[ptsg]

I looked, and all circuits have dedicated relief valves, except the "hammer/auxiliary" port, that is now used for the thumb.

Interesting. Thanks for check that and posting here.

Good thing you installed one anyway. :thumbsup:

 

[nyone]

I built my own thumb for my mini. I used the same rod diameter for my thumb as the rest of the machine. My thumb will uncurl my bucket. I haven't bent or broke anything yet. I think I habe 300hrs on this setup and cleared a lot of brush and stumps with it.