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OT/Why does my backhoe think it's a hydraulic jack??

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  • OT/Why does my backhoe think it's a hydraulic jack??

    OK...Hydraulic guys again...LOL!
    I haven't a clue...
    The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
    Everything else works fine...with lots of power even at idle.
    So "what's up hydro docs"?
    Thanks!
    Russ
    I have tools I don't even know I own...

  • #2
    Russ: I am no expert but I would guess that you have air in your lines. Gary P. Hansen
    In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

    Comment


    • #3
      Dirty spool valve...

      I was using a New Holland, (rental) and the spool kept sticking..

      Had a buddy who could really dig sitting on it digging my basement.. it stuck.. knocked the air conditioner right out of the window on the house.. He was near-heart attack.. pale.. I reassured him I would have torn the corner of the house off..

      *a guy got buried in a ditch bank cave in.. Mr Green dug with the backhoe till he saw his shirt.. Saved the guys life.. he was the best I have ever saw.. Anyways, he did in a day what I could have in a week and half. *He's deceased now.. A really nice guy I miss a lot.. The guy who got buried, he got out of the ditch, quit work.. had a lil apron and a pair of scissors the next time I saw him.
      Last edited by Dawai; 10-06-2008, 11:28 PM.
      Excuse me, I farted.

      Comment


      • #4
        Originally posted by torker
        OK...Hydraulic guys again...LOL!
        I haven't a clue...
        The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
        Everything else works fine...with lots of power even at idle.
        So "what's up hydro docs"?
        Thanks!
        Russ
        Will it develope any power while doing this?And will it hold position?

        If not you may have a cut packing on the piston.
        I just need one more tool,just one!

        Comment


        • #5
          Without being able to see the valve setup on the "hoe', I'll venture a guess or tow. First, I'm assuming that the control valve is an inline spoolvalve, with a handle for every pair of functions. As in 1 lever for bucket in/out, another for lift/drop, etc. Assuming this to be true, there will be a centering spring for each spool in the valve body. When alll the levers are in the released position, are all the ends of the spools the same distance from the casting? The reason I ask this is, is that from the end of the valve where the oil comes in from the pump, the spools move to block the flow from the pump, and send it to the function you need. So, if a spool has not returned to center exactly, it will effect the flow to the next spool in line. It's comon for a centering spring to break off a coil, or for the bolt that holds the assembly to back out a few turns. Either way, you need to be certain all spools return properly to center before moving on to the next step. Which is, to follow the likes from the function in question to the device.[inthis case, the cyl] Anything that isn't a hard line or hose will likely be suspect. A cast or machined block with ports in and out and maybe threaded caps other places will likely be a pilot operated check valve. Probably best to diss and inspect the thing, looking for busted parts, or tiny bits of debris holding the internals from doilg their intended job. Next up, there may be port reliefs on the valve. These will be inserted in the same section of the valve as the trouble is in. Usually a big hex fitting, with a spring and piston underneath. Sometimes with a visible adjusting screw and locknut.

          Let me know what these checks reveal, and I'll try to help you noodle this out. I have no hoe specific experience, only 30 years of working on garbagewagons..............Doubtless others have experience on hoe's and will offer more help

          TC

          Comment


          • #6
            Thanks guys! Yes...it holds position....not for a long time but for an hour or so(if you leave the boom up after shutoff)(I did it to check for leakdown).
            Hard to say on the power...it will lift pretty much what I ask but I have to pump the handle to lift it. It will jerk the boom up a little bit then it sounds like the pump is hitting a brickwall...sounds like it's at the end of travel or something...the slight squeal you get when you've maxed out travel...that's what this sounds like after every little "pump".(Oh Gawd...someone will have fun with all this sqealing and pumping stuff I bet)
            Tim..David.. I'll check the spools etc tomorrow. Yes...this does have a valve for each function...old tymey! No fancy fourway controls on this ol' girl.
            I'll check for valve centering etc.
            Air in the lines.. I doubt that...but maybe.
            I have tools I don't even know I own...

            Comment


            • #7
              It sounds like the relief valve for that spool is set to low...so when your raising the boom the relief valve pops off and the system goes into bypass mode-just like when a cylinder reaches the end of it's travel. You will need a gauge to properly set the relief pressure.
              Last edited by kennyd4110; 10-07-2008, 07:54 AM.

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              • #8
                Originally posted by garyphansen
                Russ: I am no expert but I would guess that you have air in your lines. Gary P. Hansen
                These systems are "self bleeding"

                Comment


                • #9
                  Hi,

                  What type of hoe is it? If it's a newer model, most likely it will have a variable displacement pump, and it sounds to me like the pump maybe be cycling between high volume mode to low volume mode. A little more info or pump manufacturer would help.

                  John

                  Comment


                  • #10
                    Because you gave 29 cents for it?

                    Comment


                    • #11
                      John...most of the guys here already know..it's an old girl...a 1969 MF 40 with a plain ol' front drive pump. Very simple...but pretty foreign to me.
                      I am not a hydraulic guy...yet!
                      Gkman...it doesn't matter what I paid..it doesn't work.
                      I have tools I don't even know I own...

                      Comment


                      • #12
                        Russ...

                        A spool valve is ported, has lil orings to separate the spool cuts.. PRESSURE is applied to parts to balance it.. when you apply pressure there on the lever it imbalances it allowing the pressure to "overcome the force" and it switches and rebalances.

                        A bad oring on the spool.. a restricted port via a piece of degraded hyd hose stopping it up.. all these things are bad.

                        My wrecker wants to stick.. I have to jiggle the levers.. old hydraulics..

                        VERY DAMN expensive to work on, unless you can figure it out yourself.. so expensive people part with the machine. A four port valve was $6,000 for a machine I was working on.

                        I'd love to do the robot lawnmower one more further.. imagine setting the "ho" up on the corner of a lot, it traveling to the site, digging a foundation level and to grade as laid out on computer cad program.. then beeping the horn when done... Lil unseen things like rocks.. well that'd make a programmer cry and pull his hair. Dozers do that routinely now.. people just sit on them being a saftey switch..
                        Excuse me, I farted.

                        Comment


                        • #13
                          Hey Torker,

                          I have the same line of thought about your pressure being off like the previous poster said or a bad o-ring in the valve. I have one, a JD 410B, EVERYTHING is hydraulic. When i got it the first thing I did was to replace every filter I culd find and change the gallons of oil. You MUST use the proper oil which is spec'd for the machine. What you find in the oil change, oil included, may give you an idea of what is going on in the system.

                          Lastly, make friends with these guys here : http://www.heavyequipmentforums.com/...splay.php?f=51

                          There's a wealth on knowledge there to be had

                          Good luck!

                          Eric
                          "To invent you need a good imagination and a pile of junk" Thomas Edison

                          Better to have tools you don't need than to need tools you don't have

                          73's KB3BFR

                          Comment


                          • #14
                            Originally posted by torker
                            OK...Hydraulic guys again...LOL!
                            I haven't a clue...
                            The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
                            Everything else works fine...with lots of power even at idle.
                            So "what's up hydro docs"?
                            Thanks!
                            Russ
                            Most likely the piston seal has failed on that ram.
                            When you pressurise the rod side of the ram to retract, the oil bypasses the piston seal, and essentialy pressurise both sides of the piston creating a displacement ram, so it pretty much hydraulic locks itself.

                            A quick test without dismantling anything is to fully retract the ram, then bump the lever to try and retract the cylinder again. If it moves out slightly, then the piston seal has failed.
                            Other way to confirm, is to fully retract the ram, disconnect the non-pressurised hose, and try applying pressure to the remaining hose. If il comes out the disconnected port on the ram, then the seal has failed.

                            As for the spool valves being the problem, given the age, they'll be a basic open centre direct acting spool. The only seals are between the outside, and the return ports. They rely on a lapped fit to provide good sealing between all the pressure lines.

                            Comment


                            • #15
                              Sorry guys...one REALLY important thing I should have said...I can push down just fine with the main boom...it just won't pull the rod in. MC...if the seal was buggered..wouldn't that cause the cylinder to lock in both directions?
                              I have tools I don't even know I own...

                              Comment

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