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Linkbelt stalls with dipper arm function

Discussion in 'Excavators' started by Ratmotorhead, Jul 10, 2018.

  1. Ratmotorhead

    Ratmotorhead Well-Known Member

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    Hello,men I have been working with my 4300c linkbelt this summer and I have been getting a bog when I pull in the dipper. I put my guages on dipper in and out and when I pull in the stick in to relieve both my guages rise to about 3000 psi, then dipper in guage goes to 5000psi and stalls. I cannot get any adjustment out of dipper in or out, so I switched relief valves from boom since they are same part number and adjust up to 4500 like they should and I get the same result. Since both guages go up upon moving dipper in that is telling me it is deadheading itself because of a worn spool or bad packing or gouge in dipper cylinder. Have any of you tried to isolate either or by capping the dipper in line hose and see if it goes to relief? If it goes to relief that tells me it is bypass to dipper out side of cylinder, if it still only goes to 3000psi and won't adjust that tells me it is bypassing at spool in hyd valve. Any thoughts guys. By the way, the hyd pumps, bucket, and boom, and pilot pressure all adjust to my book specs.
     
  2. Coy Lancaster

    Coy Lancaster Senior Member

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    What hydraulic pump do you have on this machine and how many hours on it? You could have a problem in the regulator on the hyd. pump. The o-ring on the reg. could be bad and letting oil get behind piston not allowing it to move.
     
  3. funwithfuel

    funwithfuel Senior Member

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    Is there a point in rod travel where the crowd function stalls repeatedly? Or will it jam up anywhere along rod travel? By your description, in my opinion, you might have something blocking oil flow. Perhaps a flapper in a hose, or maybe a piston nut backed off blocking oil port of cylinder
     
  4. Coy Lancaster

    Coy Lancaster Senior Member

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    He didn't mention any binding or damage on the rod or cylinder. All your suggestions are good ones and need to be addressed. But it is easier to start with the basics.
     
  5. funwithfuel

    funwithfuel Senior Member

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    Wow, I just reread the original post. 3000 on both sides crowding in? I think you should dead head your dipper hoses and retest. You should have pump psi on one side and tank on the other. Of course these values should flip in reverse function. If your pressures are now stabilized where only one gets pressure at a time, you will want to look into your dipper cylinder. Do you have line rupture valves on this ol girl?
     
  6. Ratmotorhead

    Ratmotorhead Well-Known Member

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    Thanks for the response guys, the pump is a uchida hydramatic ksj1282 . The guages seem to both go up at the same time until 3000psi then the dipper out side goes to 0 psi then dipper in side rises to 3000 psi then continues to almost 5000 psi and starts to bog. I have swapped out both relief valves with the boom and the boom side both adjusted as it should. That tells me reliefs are good. Right now I have the regulator off and do have some slight scoring on the upper spool which does not move as freely as I would like. I removed the inlet oil pipe to check out if the plates moved freely from left to right and both upper and lower and they do. No springs broke and seems good. I still have questions about electric solenoid on regulator and wonder if it in should have 24volt power while running or if it functioned during mode changes and changed pump during fine dig and power and limp mode,I will research that more while inspecting regulator where it's fluid porting goes.
     
  7. Ratmotorhead

    Ratmotorhead Well-Known Member

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    It doesn't have any visible scoring on rod, but I might have some internal issues on its gland. Iam showing no swarf or shavings in filters, but I did remove a lot of it when I started this project . Is there a place I could get info on regulator adjustments, or an idea of how it functions , as for now I am leaving all adjustments alone. I understand that when a control function is moved the pressure drop causes the regulator to move, that's where the two lines from left and right hyd valves go to regulator at top and bottom. I will do some work on polishing bores and spools for free movement ,as this component has not been touched yet . Hope to get to it by weekend,but work has me moving a crown of a stamp press at 225 tons. Fun fun fun!
     
  8. funwithfuel

    funwithfuel Senior Member

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    Do you have the ability to monitor each side of the spool? I know you were measuring A&B of the cylinder but can you measure servo A&B simultaneously. I am wondering if you have an rcv problem perhaps? Trying to see where you would have 3k on each side.
     
  9. Ratmotorhead

    Ratmotorhead Well-Known Member

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    My test ports are about 8 inches above the left hyd valve in steel lines going to hyd cylinder they are close to spool. It's an old machine 1985ish has no computer , this machine really had a monitor basically
     
  10. John C.

    John C. Senior Member

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    As I recall there was a throttling function in the stick circuit. Basically the stick can fall faster than the pumps can put out so there was two pump flow going to the piston side of the cylinder but the return circuit would only allow the flow of one pump to get back to the valve and then to the cooler. If you follow the piping from the valve halves you will see a pipe from each valve block meeting and going to the cylinder but only one pipe going back into the valve. I don't think there was a throttling valve in those older machines yet but you might check for an extra block installed on one of the lines. Load lock valves are another possibility. They were an option on other manufacturer's machines and could have been for this one also.
     
  11. Ratmotorhead

    Ratmotorhead Well-Known Member

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    Thanks guys for the info, much appreciated. My machine does have the connection block at the dipper in lines , and it does connect at both hyd valves . And one return line to valve from dipper out line, just as John c says ,but no other blocks on those lines. Or locks for that matter. I am making sure now that pilot oil is getting to the correct place from both halves of hyd valves to the regulator,and that the direction of oil is going where it needs to go when that solnoid is energized . I am learning a lot on the bench right now,and may get to the bottom of this.