Hello. Im having problems with my thumb. It has good clamping pressure and speed, but the return is week to non existant. I swaped the hoses and the problem followed, as in the clamping pressure was nil and the return was fast. Way to fast. In the pics you can see the block that the hoses attach to. The larger pipe feeds the bottom of the cylinder. The thumb will creep down after I shut off the machine. Any ideas guys? Jason
Does that have the electronic thumb control on the right joystick? If that switch on the joystick gets too dirty it won't make a good connection to open the hydraulic valve.
The machine is a 1994 so no joystick, just leavers. The thumb control is a foot pedal on the floor. Jason
Hmm. I dunno what it would be then. Maybe a bent and crimped pipe? Have you watched the valve to make sure that it moves fully in both directions when moving the foot pedal?
The pipes seem fine. I dont see any valve moving. When you say valve moving, are you referring to the orange block where the pipes come into? Jason
No, the valve that controls the thumb should be in front of the oil tank under the cover to the right when you're sitting in the seat. If you open the engine cover and then the side cover, you should be able to watch which valve moves when you move the foot pedal. There is a cable that goes from the pedal to the valve. Same as for the blade and boom swing. I just had another thought. Is that orange box on the dipper a manual valve or something in case you don't have the attachment on? I'm not real familiar with how aux hydraulics work.
I will look at that valve tomorrow. Thank you. I'm not exactly sure what the orange box does, I think it might have something to do with using a hammer. Looks like there might be some kind of return line on it. Jason
The valve seems to be ok. Doenst seem to be anything wrong with it.
Is there a valve to switch from 2 way function to breaker function? That might explain the high speed one sided symptoms you're having/
might well be under the floor plate
So the valve moves fully in both directions? I've had a small stone or something similar get stuck under the pedal that keeps it from opening all the way... Other than that I'm out of ideas
I dont know how the breaker function would work. (which way to push the peddel etc). Ive been going through a service manual but havent seen anything so far. Ill check tomorrow for a valve. Thanks for the help guys!
I have to admit I know nothing about the Kubota system, but was curious and did a little search. Is that a KX71, or a series machine like KX71-3? If it's a straight KX71, as Mater pointed out, it has a foot pedal that operates a control cable connected to valve spool, I'd look real close if that control cable is moving valve spool fully. Not sure what the manifold block on side of boom is, and parts pages weren't much help, simply called it a "block", well...duhh. :Banghead Could you get some more pics at different views of that "block", I'd wager it switches aux circuit from single acting to double acting, but can't say for certain.
Thank you willie. Ill get more pics on tomorrow, and take a good look at the underside of the foot pedal. Its just a KX-71. I couldnt find anything in my shop manual that helped me, but then again im not a mechanic.
No worries Someotherguy. I did find Kubota parts pages online, it shows the KX71 is a cable operated control valve, I'd look real good to see that the cable is moving control valve spool fully.
in your first picture , that could be the vale to make the circuit double acting , it looks to have a square nut to turn , have you given that a try
I looked underneath where the foot pedal attaches to the cable. Everything seems to be operating like it should. The square nut on the block seems to be just a plug for that hole. I have had it out before and it just leaks out some hydraulic fluid like I would expect. Tonight I will look at the service manual again and see what I can find. Thanks guys. Jason
Hi Willie. Here are some more pics of the block, and the control cable attached to the foot pedal. Jason
Again, I don't know that machine, but I'll wager your problem is caused by that line connected to the side of that junction block on the boom. I know it's going to be difficult to verify this because it's a mini-ex and it's terribly difficult to follow hoses on those things, but you need to see where that hose that's connected to the side of the block goes. It's my guess that hose is used during breaker operation, which doesn't send return oil back through control valve, but returns oil more directly to tank. If you need to remove machine covers, find where that hose goes. It might go to a manual operated valve or a solenoid operated valve. If you can find that, see if the other connection to that valve goes to tank and no where else. If it does, disconnect that hose connected to side of junction block on boom, and where that hose connects to panel on front of machine, cap those fitting with appropriate caps, and try your thumb. I'll go out on a limb and wager it will work proper now.
That hose on the side is a return. It goes to a bank with a few other hoses. I spoke to a local Kubota mechanic today. He told me that there would be an adjustment I could make on the control valve assembly. He believes that the close pressure is set to high, and the open pressure is set way to low. Problem is, I dont see where there is any way to adjust the spool section. (evident in the pics?) I think you are more on track here Willie. Im going to see if I can maybe bypass the block, or disconnect the return and see what happens.
Video didnt imbed. Here is the link. http://youtu.be/BV8rJJe09lY
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.
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
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.
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.
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?
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.
Willie. What would you recommend for limiting the thumbs pressure? Jason
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.
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??
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.
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.
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
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.
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
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
Thanks Willie!
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?
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.
Great explanation, thanks!
Great thread on the Kubota Kx model no relief valve problem. I have a Kx61-2 that when I purchased it had bent bucket pin due to PO using both bucket and thumb hydraulics at same time. I use mine as a manual thumb hoping to get info on how to adjust-since that won't happen anyone fixed there Kx yet ? Pics? Thanks
Here is a pic of what I had to do to relieve my Aux line. Should have done it a long lime ago. It's pressure adjustable for the times I use other attachments (ie wood splitter). The return line frome the valve goes to the return manifold onder the seat (capped from factory). It steps down to .25" is the only problem I can see, however it does work. Thanks for the advice (you know who you are).
Very nice work TCM. And the way you have it configured, wouldn't be hard at all to add an additional relief on the other line.
Thanks for pic, I have the same Aux line Configuration on my Kx, Having the valve one line is its operated to where you set the thumb in place and then the bucket will over power the thumb? Thanks.
Yes it will. In addition I have the quick couplers opposite each other so you can't mix the lines up. That is a single relief valve only relieving one side of the aux circuit.
Hello Willie59, please have a look at my valveblock of my Kubota U50-3@ 2006 model: I am about to install a hydraulic thumb and need to make sure I will not ruin it straight away. Most of my circuits/spools here have 2 relief valves (one on each side of the valveblock) and I don`t see any other "in line" valves (I can follow the lines from the spools to the hydraulic cylinders without finding any extra valves). When reading your explanation above it sounds like these relief valves will not fully protect the bucket/stick/ blade etc. if they are inflicted forces upon while not in use.. Is this correct? I want to connect a thumb to my aux spool and hope that i only need to mount in relief valves just as the bucket/stick and blade already have in their spool. I am hoping these valves dump the oil to their "twin line" from the same spool + tank (if it is coming from extension side of piston)... Would be very grateful for any explanations
Hi Justin, I can't say for certain because I'm not familiar with your machine, but those reliefs you have marked look like port reliefs for the noted functions. If they are port reliefs, they will pop open and relieve the cylinder/function noted even when the spool is centered. Not sure about your aux section, I see something that looks adjustable in that port, just can't tell if it's a port relief or not. If you could get your hands on the hydraulic diagram for your machine you could get more info from that, might even get some useful info from the parts pages, I think you can look up Kubota parts pages online.
Justin, on my Kx there was NOT a relief on the aux port. As stated above it will cause problems. Corrected problem by installing a adjustable inline relief valve. See pic
Before & after install pic
Ummm.... Jack? Read back on this thread, Willie's explanation about how the exact valve you're using is dangerous in a two way cylinder application. I've lost the pictures, but I proved it to my then boss thirty years ago when a valve that looked very much like the one you have there literally blew in half the length of the casting. This was after upgrading hoses several times because they kept blowing ends off and such before I was employed there. You have to have a tank line to handle the relief flow, you can't just move oil from one end to the other.
Thanks Willie59, Jack and Lantraxco for you comments! Could you have a look at the attached the parts diagrams for my aux and bucket spool? And tell me if you think these relief valves on the bucket spool are port reliefs? (They are described as "Assy relief valve" in the parts list..) The corresponding parts in the aux parts list are described as "Assy valve shut of"..They do not look as if they contain any spring, so I can`t believe they have any valve function.
Here is my aux spool diagram/parts list:
Yes, the diagram for the bucket spool section shows port reliefs, item(s) 180. The diagram for the aux spool section with the assy valve shut off, that's not a port relief valve, but it is installed in a port relief port. To try to explain it as simply as I can, the way those type of valves work is when the spool is in the center position the work ports, typically called A and B, are blocked from both oil input from the pump (P) and oil output to the tank (T) by the spool itself. In other words, the oil in lines connected to A and B, lines that go to cylinders/motors, is effectively trapped in in those lines by the spool in the centered position. If the attachment that is connected to ports A and B encounter an external force, putting external force pressure on either A or B, at some point something has to give. That's where the port relief comes in, it's an internal (inside the valve) route for oil under pressure in A or B to escape and exit to tank (T), by-passing the spool. In the case with your aux section with the "assy valve shut off", basically that's plug that plugs that internal route between A and B and the internal tank porting, it blocks off that route. If it were not there, when you worked a function connected to A or B on the auxiliary section oil would simply go right through the valve to the tank porting, no work could be performed with A and B lines, so they plugged that internal port. That also means you have no port relief on the A and B of the aux section because of this plug. However, it's very possible that the relief valve cartridges that are used in the other sections, such as the bucket section, will fit in the port relief ports on the aux section. Remove the "plugs" and install relief cartridges. I can't say for sure this will work because I don't know that machine, but a Kubota parts guy should be able to confirm this.
Hello Willie, Thank you very much for your splendid explanation. That is what I also wanted to hear, so now I will just need to buy a couple of these port reliefs and install them straight in the aux spool
That's what it looks like, but again, I'd confirm with Kubota
After some searching on the internet I find that these original relief valves are really heavily priced... $330 each ! I found a stock with just the one for half the price which I have ordered. And now I am wondering if I can manage with just the one..? Does anybody have a opinion whether it is just as important to have one on the "extension side" of the thumb cylinder?? I am wondering if I could manage without a pressure relief valve on that line, and rather be careful not to put external force on the back side of the thumb.. Or will the fully retracting the cylinder then cause damage?
If that's 330 US Dollars, actually that's not bad, I've paid over $800 for Kobelco port relief valves. But hey, sometimes the wallet gets thin, I know that feeling. In a pinch, if you're the only one operating the machine, yes, you could get by with only one relief valve on the extend side of the cylinder. No, it's not the ideal set up, but do-able if you keep your wits about you when retracting the thumb.