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Thumb problems KX-71
- Thread starter Someotherguy
- Start date
willie59
Administrator
Someotherguy, the pics that you posted are what is called a "sectional valve assembly". It consists of an inlet section, feed from pump, and an outlet section, return to tank. In between are the various operation function sections, stacked together, boom, arm, bucket, etc. That "section", whatever function it is, that you noted as an "adjuster", that adjuster is actually a relief valve for that particular section. And the section that you noted as "thumb spool" section, it doesn't have relief valves, which puzzles me, just where are the relief valves for the aux circuit?
But that's a different issue, not to get side tracked on that. I would like to know where that hose that connects to the side of the manifold block on side of boom runs to myself.
But that's a different issue, not to get side tracked on that. I would like to know where that hose that connects to the side of the manifold block on side of boom runs to myself.
Someotherguy
Well-Known Member
From what the mechanic said to me, the relief valves would have been right there.
I have a PDF file that shows where the 3rd line goes. I can email it to you if you pm me your addy.
Thanks.
Jason
I have a PDF file that shows where the 3rd line goes. I can email it to you if you pm me your addy.
Thanks.
Jason
willie59
Administrator
Well, I'm only looking at pics, and not one to disagree with a Kubota mechanic who knows far more about that machine than I do, but I don't see any relief valves in that aux section. As for the email addy, I'll send it to you, but fixin to say "stick a fork in me, I'm done" here for the eve, likely be tomorrow evening before I get a look at it.
willie59
Administrator
Well, viewing parts pages, looks pretty clear, hose #010 is return to tank. It's the hose on you machine that connects to the side of the manifold block on the side of your boom, then connects to bulkhead fitting on RF panel on machine. From there, hose #070 connects to bulkhead fitting and goes back to that return manifold pipe shown on right side of pic (no part # shown). The purpose of this line is for when you use an attachment that uses single acting hyd circuit, like a breaker, plate compactor, etc. A thumb (double acting circuit) won't work properly with that hose connected.
Remove the hose, install proper hyd cap on fitting on manifold block on boom and on bulkhead fitting on machine panel. But before you remove fitting connection at bulkhead fitting, remove your filler cap on hyd tank and apply a little vacuum from a shop vac, otherwise you're going to dump some oil when you remove that connection to the bulkhead fitting. A good hyd hose supply shop should be able to provide you with the proper fitting caps required.
Remove the hose, install proper hyd cap on fitting on manifold block on boom and on bulkhead fitting on machine panel. But before you remove fitting connection at bulkhead fitting, remove your filler cap on hyd tank and apply a little vacuum from a shop vac, otherwise you're going to dump some oil when you remove that connection to the bulkhead fitting. A good hyd hose supply shop should be able to provide you with the proper fitting caps required.
Someotherguy
Well-Known Member
Thanks Willie.
Tonight I removed the side hose from the block and it gushed, even though I had it above the tank. This told me where it terminated.
I spoke to anothe mechanic this afternoon and he showed me a leaver for a valve (on a newer kx110). He told me that if it was open even slightly that the thumb would not return. Ive started looking for a hidden valve.
Now I have the service department all scratching their heads at how to go about NOT applying full pressure to the thumb.
I think you are dead on Willie. What do you think about adding a valve to the hose instead of removing and capping off?
Tonight I removed the side hose from the block and it gushed, even though I had it above the tank. This told me where it terminated.
I spoke to anothe mechanic this afternoon and he showed me a leaver for a valve (on a newer kx110). He told me that if it was open even slightly that the thumb would not return. Ive started looking for a hidden valve.
Now I have the service department all scratching their heads at how to go about NOT applying full pressure to the thumb.
I think you are dead on Willie. What do you think about adding a valve to the hose instead of removing and capping off?
willie59
Administrator
You can add a valve, no problems doing that, but it all you ever plan to do is use the thumb, I'd just remove the hose and cap the fittings. If the case ever came up, that you were going to fit a breaker or compactor, you could always put hose back on.
If we trust the parts manual that you sent me, you're machine doesn't have a valve, hidden or otherwise, that hose goes directly to the return manifold.
If we trust the parts manual that you sent me, you're machine doesn't have a valve, hidden or otherwise, that hose goes directly to the return manifold.
Someotherguy
Well-Known Member
Willie. What would you recommend for limiting the thumbs pressure?
Jason
Jason
willie59
Administrator
Well that's the thing, I have gone through the parts manual, although not with a fine toothed comb, but I have yet to find the relief valves for the aux circuit. I'm still baffled by that.
Someotherguy
Well-Known Member
Lol.
So are the guys at the Kubota dealer. :tong:beatsme
One mechanic was (thinking out loud) about the possibility that the "main" (cant remember his exact words) relief valve being used in loo of the aux having its own.
I was wondering, if there is some kind of relief valve/limiter that I could install at the aux circuit??
willie59
Administrator
The main relief valves would be in play for aux circuit when circuit is in operation, moving spool to operate thumb. But once you take foot off pedal and center aux valve, main relief valves have no role in pressure on aux pipes. That's where you typically find port reliefs on a valve section, I don't see port reliefs. Without them, you could apply excessive force to thumb cylinder and bend thumb cylinder.
There is one possibility, I can't say this for certain though, that spacer section next to aux section, not the section on the outside, the section inboard on aux section, that spacer section has two plugs in it, it's possible those ports are for fitting port reliefs for the aux section by adding proper relief valves in those ports. I don't see this info mentioned in the parts book, and it's just a wild guess on my part, but it's a possibility.
There is one possibility, I can't say this for certain though, that spacer section next to aux section, not the section on the outside, the section inboard on aux section, that spacer section has two plugs in it, it's possible those ports are for fitting port reliefs for the aux section by adding proper relief valves in those ports. I don't see this info mentioned in the parts book, and it's just a wild guess on my part, but it's a possibility.
mitch504
Senior Member
I'll bet you a nickel that's what that block is, a relief valve for the thumb. That would explain it having a return line on it.
Someotherguy
Well-Known Member
Willie, thank you for all your help.
I really appreciate all the replys I have gotten here. Ive learned more in 4 days than I could have ever learned just by studying my shop manual.
Jason
I really appreciate all the replys I have gotten here. Ive learned more in 4 days than I could have ever learned just by studying my shop manual.
Jason
willie59
Administrator
Send me your nickel then mitch, there's no components in that block on side of boom, it's simply a manifold block. Sorry.
Glad to help, even if I'm just winging it.
Someotherguy
Well-Known Member
Ok. Willie is five cents richer.
I took the hose off and put a plug in it. Rooted around in that block and found nothing in the way of springs balls and the like.
I then put a plug in the block and the thumb works like it should, albeit with to much pressure. I guess I'll have to treat it
like a manual thumb and bring the bucket to it.
As soon as I figure out how to install the relief valves I'll post that.
Thanks for all the input guys, and Willie gets the gold star!
Jason
I took the hose off and put a plug in it. Rooted around in that block and found nothing in the way of springs balls and the like.
I then put a plug in the block and the thumb works like it should, albeit with to much pressure. I guess I'll have to treat it
like a manual thumb and bring the bucket to it.
As soon as I figure out how to install the relief valves I'll post that.
Thanks for all the input guys, and Willie gets the gold star!
Jason
willie59
Administrator
Good news indeed Someotherguy. Now where's my nickel mitch?
I would first inquire with Kubota about relief valves for the aux circuit, what's available and where they're located. Will probably be a little expensive, but so will fitting something aftermarket.
If you want add aftermarket valves, you don't wan't to use crossover relief because of the difference in displacement on the two sides of the hyd cylinder. What you need to use is two direct acting relief valves, one for each of the two aux lines, with reverse free flow check. That junction manifold on the side of the boom would make a handy connection point to rig up these valve and the hose you now have disconnected will provide the needed connection to tank for the relief valves. The valves are adjustable, and the reverse free flow will provide anti-cavitation when you pop open the opposite relief valve and make the cylinder move.
http://www.hydraforce.com/Pressure/Pre-html/6-022-1_RVCV56-20/6-022-1_RVCV56-20.htm
I would first inquire with Kubota about relief valves for the aux circuit, what's available and where they're located. Will probably be a little expensive, but so will fitting something aftermarket.
If you want add aftermarket valves, you don't wan't to use crossover relief because of the difference in displacement on the two sides of the hyd cylinder. What you need to use is two direct acting relief valves, one for each of the two aux lines, with reverse free flow check. That junction manifold on the side of the boom would make a handy connection point to rig up these valve and the hose you now have disconnected will provide the needed connection to tank for the relief valves. The valves are adjustable, and the reverse free flow will provide anti-cavitation when you pop open the opposite relief valve and make the cylinder move.
http://www.hydraforce.com/Pressure/Pre-html/6-022-1_RVCV56-20/6-022-1_RVCV56-20.htm
Someotherguy
Well-Known Member
Thanks Willie!
TCM
Well-Known Member
I have a KX 121-2 and I can confirm there is no factory relief valve or option for one in the valve block. I too will have to go with an external valve and it will be aftermarket. Kubota dealer told me they sell an after thought valve for three times the price as you can find it on the street. I will be mounting it in the same location as you someotherguy. All you have to do is connect a single relief at that location and you already have the return line to the tank. I believe you will only have relief protection in the one direction. Willie, I just purchased a cross over relief for this purpose because I have no extra return line to the tank. I'm haven't connected it yet and why do you think it will not work even if the valve can accommodate the GPM?
willie59
Administrator
A crossover relief won't work properly on a hydraulic cylinder circuit, it will only suit half of your needs. There a basically two needs for a relief valve on both lines of the thumb cylinder.
1) when you are operating the pedal to move thumb cylinder, say you're extending the cylinder until it reaches the end of cylinder stroke, cylinder bottoms out, but you continue holding pedal down. This will pop open the relief from line A (pressure line) and divert it to line B (return to tank through control valve). In this situation, it will work properly.
2) the situation where it won't work properly is you have the thumb cylinder extended, then roll the bucket into the thumb to grab something, but unintentionally roll bucket too hard into thumb, too much pressure for thumb cylinder to withstand. Relief pops open, main control valve ports are closed (you're not using the pedal), sends oil from piston side of cylinder to rod side of cylinder, but in this circumstance the cylinder can not retract because of difference in displacement between piston side and rod side of cylinder. In this case, there is a chance you could bend your thumb cylinder rod.
The only way you can properly protect a cylinder with an "in-line" relief arrangement is to provide a dedicated line to tank to dump oil.
1) when you are operating the pedal to move thumb cylinder, say you're extending the cylinder until it reaches the end of cylinder stroke, cylinder bottoms out, but you continue holding pedal down. This will pop open the relief from line A (pressure line) and divert it to line B (return to tank through control valve). In this situation, it will work properly.
2) the situation where it won't work properly is you have the thumb cylinder extended, then roll the bucket into the thumb to grab something, but unintentionally roll bucket too hard into thumb, too much pressure for thumb cylinder to withstand. Relief pops open, main control valve ports are closed (you're not using the pedal), sends oil from piston side of cylinder to rod side of cylinder, but in this circumstance the cylinder can not retract because of difference in displacement between piston side and rod side of cylinder. In this case, there is a chance you could bend your thumb cylinder rod.
The only way you can properly protect a cylinder with an "in-line" relief arrangement is to provide a dedicated line to tank to dump oil.
TCM
Well-Known Member
Great explanation, thanks!