Thumb hydraulics

[Justin Payne]

Sorry for maybe bothering people with yet another thumb hydraulics post. But yes, I have read most of the other posts about the topic, but I still am a bit confused, especially when trying to investigate and understand how my own machine (Kubota U50-3@ year: 2006) is set up..

Here is a picture of my valve block. The AUX spool is the top spool, (just the smaller “outlet block” on top of that again). It looks as though that my AUX spool does not have relief valves on either side (as e.g. the bucket, stick and blade).

Q1: Are such relief valves “active” when the not using this specific spool? (I don`t see any other of the lines/ circuits have any other extra “in-line” relief arrangement.. If I for example are not using the stick, and start accidentally pushing or pulling really hard on something by other means, (e.g. running the tracks) will one of the “Stick relief valves” open? If not I am wondering what will open to protect the stick in such a situation? I suppose that if I am forcefully compressing the stick cylinder it will not help either (because of the volume differences in the cylinder) But I don`t see any “in-line relief arrangement with dedicated line to the tank” for any of the circuits (aux, swing, bucket, boom, stick etc..)

 

[Justin Payne]

What I really hope to hear is that these type of relief valves are always "active" and that they dump the excess oil to their "twin line" (in the same spool) + internal valve block return line.. Then all I need to do for a thumb install is install two such relief valves and adjust them so that the bucket overpowers the thumb and that they are well below the thumb cylinder max pressure

 

[007]

Hi Justin,
I will try to help but if i get something wrong im shore someone will tell us.
What makes you say the bucket stick and blade have dual relief?
they are not shown in picture or are they under side of spool?
I would have said apart from the main oil relief valve you only had one shown being blade down, stick in and bucket curl in.
I believe the line relief valves in your picture would be active even if spool not in use and the relieved oil would return to tank through the middle of the spool.
I would hope you are not doing this intentionally but if load came on your stick because of operating tracks the relief shown should open going backwoods and i am not shore you would be protected going the other way.
Interesting question maybe someone might enlighten us.
So my question to you is if the manufacturer only fitted additional relief valves on the circuits being stopped all the time by digging or lifting the machine up why would you worry about dual relief on your thumb?
As long as you make shore the one you have on aux spool is piped to the crush stroke why worry about retract.
Naturally your thumb cylinder would have to be like the kubota cylinders and be rated for main system pressure.
Cheers

 

[Justin Payne]

Thank you 007
All of the spools that show a relief valve in the picture (bucket, stick and blade) had two relief valves. There was one on each side of these spools. (opposite sides). It is difficult to take a picture of the other side since the wall of the cabin is very close by. So for some reason Kubota mean that both sides of these circuits need protection. I can certainly see situations where one can accidentally overload both sides of these circuits. I suppose, also the thumb; If the thumb is extended quite a bit and one pushes it down on the ground with full force?

 

[007]

Yeah no problems, the reason i said that because a couple of us here were looking at a bobcat hydraulic schematic a few days ago and it only had single relief on those circuits.
I should have not been lazy and gone out and looked at mine.
I have the U25-3 and they do not have the 1/2 way valve like yours.
All you get is Aux spool with two reliefs.
Are you thinking of fitting a thumb on yours?

 

[Justin Payne]

Yes, I am about to order a pin on thumb from Showtime Fabrication.. I I suppose, one or to relief valves from somewhere..

 

[007]

Not shore if you have picked up on quiet a few people on this forum with thumbs which won't hold the pressure and let the object you are holding go.
I have that problem with mine also and mine is in a hydraulic shop now getting an extra valve fitted to keep the relief valves from leaking the pressure away.
will know if it is fixed in a few days hopefully.
Cheers

 

[lantraxco]

Coming in late, yes all port reliefs are always active to open the work port to the tank return, they also incorporate a check valve to provide makeup oil to the opposite work port. You can't dump oil from one side of a cylinder to the other, going one way you starve for oil and pull dirt in with air around the rod, the other way you have too much oil and something explodes, thus the port reliefs dump to the tank return galley.

 

[Iron@Dirt]

you will need cylinder max pressure from builder and adjust to recomendation.