adding a thumb to Kubota KX-018

love2havefun · May 4, 2020

I recently purchased the above machine with 105 hours on it, nice machine!
I want to install a hydraulic thumb, the thumb manufacturer (AMI) recommends that the auxiliary hydraulic pressure to be set to 1800 PSI , it is currently at 3100 PSI.
I am unable to find out any information on how to adjust the pressure down on Kubota's auxillary circuit, hoping you can help here. Can you please advise or point me in a direction, the dealer I contacted did not know how to do this and recommended I leave at 3100 but I am concerned because the thumb pressure is to be lower so that when curling the bucket it will overcome the thumb pressure which isn稚 going to happen at 3100. I have looked at pressure regulators but not sure if I can get a return line back to hydraulic tank and if there is anywhere to tie it in? Also if there is a regulator what is happening to the pressure in the cylinder when the bucket tries to curl it back and there is no place for fluid to go?
I look forward to hearing back

oldnslo · May 5, 2020

The auxiliary valve might have work port reliefs built into it. If not then you would have to install some form of external pressure control. This could possibly be added close to the valve which would make the tank line easier to access.

love2havefun · May 5, 2020

Hi Oldnslo
Thanks for your comments, appreciated. I think I have two issues:
- first is reducing auxiliary line from 3100 to 1800 psi, a regulator will do that provided I install return line connected to tank, you agree?
- dumping pressure from thumb cylinder created when bucket curls up back to tank tied into above, you agree here as well?
I'm not sure what will do this?

oldnslo · May 5, 2020

Love2,
There are a couple of different options for limiting clamping force - pressure on the thumb.

1) Simple relief valve installed on the cap end of the cylinder connected directly to the tank line. This would limit pressure in that line to whatever you set the relief valve to but would also dump pressure whenever this valve is actuated. This also allows the thumb cylinder to retract when you curl the bucket. Down side is that it draws a vacuum in the rod end of the thumb cylinder. Probably not a major problem but will cause the thumb to be spongy. Again your auxiliary valve might have anti-cavitation check valves to prevent this from happening.

2) Pressure reducing / reliving valve installed in the cap end of the thumb cylinder and tank line connected directly to tank. Reduces pressure to the thumb but does not dump excess flow to tank causing complete system pressure to fall. Relief function would allow cylinder to retract same as relief valve above.

Post more questions if you have them.

love2havefun · May 6, 2020

Hi and thanks for your comments. I was thinking of doing #2 and adding check valve so that when bucket is curling up the fluid in thumb cylinder can exit to tank return line. Sun Hydraulics has manifold, cartridge (PPDBLWN) and check valve. Now I need to see if I can install a return line to tank. Never done one, not sure if you have? Anything I need to look for ( hopefully an open, spare port?)

oldnslo · May 6, 2020

For tank connection you can just tee into the existing tank line of your valve stacks.

Looks like a Sun E2? would have the cavity for the reducing and check valve that allows free flow around the reducing valve so that you can open the thumb. The relief port of the reducing would connect to tank and this is what would allow the thumb to move when external load is applied from curling the bucket.

Seven Gables · May 6, 2020

Before you go through too much extra work, I would make sure you don't have work port reliefs like was mentioned. I don't know about your kubota but a lot of machines have them built in to both sides of the auxiliary control valve , makes it very easy to adjust pressure relief setting on that circuit. Find that auxiliary thumb valve and look for a Allen head bolt with a jamb nut. The important thing is to set this thumb relief pressure to less than the thumb cylinder is rated for. Hard to believe your kubota dealer doesn't know? If it has this port relief it will save you a lot of frogging around. Do you have access to hyd pressure test gauge?

love2havefun · May 6, 2020

Hi
Thanks for your email
Yes I have hydraulic pressure gauge. I looked as best as I could where valves are, took a cap off one, couldn't find anything to adjust

, it's nice an easy area to find things but will be checking again tomorrow. I also have to find tank return line to see if I can tie into it.

The Sun Hydraulics pilot operated pressure reducing / relieving valve is a PPDBCWN.
I was really surprised that the dealer wasn't aware, they just said they have installed a lot of these thumbs and leave hydraulics at factory which isn't making sense to me but I have a LOT to learn in that dept.

love2havefun · May 6, 2020

As an FYI the thumb manufacturer states that thumb pressure should be at 1800 psi, the Kubota auxiliary circuit is delivering 3100psi. The way I understand it is that if the thumb isn't less that the bucket it wont move up as bucket curls.
Comments are welcome