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Pilot pressure pulses

Discussion in 'Excavators' started by 360joe, Jun 3, 2008.

  1. 360joe

    360joe Well-Known Member

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    Location:
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    Have a Hitachi EX120-3 which has a pressure pulsation in the line from the pilot pump. You can see the hydraulic line from the pump to the pilot filter twitch and feel it if you put your hand around it. It's always there and happens every 1-2 seconds. It is alot more noticable when machine is warmed up. Thought it might be the bypass on the pilot filter operating but replaced the filter and no change. Can anyone tell me if this is normal and whats the cause. The machine appears to be operating fine.
     
  2. Reuben

    Reuben Senior Member

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    ours did the same thing, same machine also. We got rid of it so I never found it what it was. I know the machine seemed to over heat very quickly.
     
  3. JS580SL

    JS580SL Senior Member

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    Is it the origional hose? I was told that you have to use a specific type of hose so that it cant flex and throw the control response off.
     
  4. 360joe

    360joe Well-Known Member

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    Reuben, did the machine have the same issue from new or was it something that developed with time? I have my machine about a year and it had approx 7k hours on it when I got it. It had these pressure pulses then and it has been kinda annoying me since. Didnt follow it up as its operating fine and I dont know if it is something I should be concerned about. I suspect its temperature related although I dont know. The main hydraulic circuit will have a temperature controlled valve that operates to divert oil around cooler when its warming up but dont think the pilot circuit has the same design. I think its the original hose still fitted between the pilot pump and filter.
     
  5. Reuben

    Reuben Senior Member

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    You know I really never knew when it started just noticed it one day and then every day after that. And ours also ran just fine. But it would pulse so bad you could hear it. Ours had about 3500 hrs on it when I first noticed it.
     
  6. ncbschzzt

    ncbschzzt Well-Known Member

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    Occupation:
    john deere/hitachi field tech
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    The pilot circuit does not have a thermal bypass, first thing is you guys need to change the filter as it is a pressure side filter. Any blockage will cause this all day long, also these machines may have internal leakage in the pilot circuit. Also are front attachment speeds slow?
    1. change filter
    2. install 1000psi gauge between pump and filter, record pressure (should be around 300-500psi)
    3. If pressure is off, most likely problem is in pilot pressure regulating valve
    4. If PPRV is determined good then problem may lie in any one of the functions that are activated by pilot pressure, control valve, pilot controllers, shift solenoids.....
    Start simple.
     
  7. 360joe

    360joe Well-Known Member

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    I suspected the pilot filter and changed it but it made no difference at all. I then suspected the pilot pressure relief valve and so I dismantled it. I could not see any obvious flaws with it. I cleaned the fine mesh screen between it and the check valve and reassembled. Still no difference. The pilot system obviously connects to alot of different valves, solenoids etc so I think fault finding on it could be difficult. It would give a clue if some of the machine functions were not right but all controls seems to work fine. I now suspect the acculumator. I think perhaps its lost internal pressure over time and is now failing to cushion the pilot system properly. I think this could cause the pilot relief valve to oscillate and produce the effects I am seeing. Anyone ever see this happen or know if there is a recommended replacement interval on the accumilator? Surely it loses some pressure over the years?
     
  8. Iron Horse

    Iron Horse Senior Member

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    Have you recently had a quick hitch fitted ? Because the hitch line goes directly to the pump it can cause these problems .
     
  9. ncbschzzt

    ncbschzzt Well-Known Member

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    I have a fix......
     
    Last edited: Jun 20, 2008
  10. kirbyt

    kirbyt New Member

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    I owned an ex100-2 for two years and the pilot pulsed as you described. I contacted the local hitachi dealer about the problem and he said "when it stops pulsing then you have a problem" something to do with pilot pressure relief/dump valve. Machine starts doing it as soon as hydroulic system is warm. I dont own the machine anymore but It's still in my area working and it still pulses.
     
  11. ncbschzzt

    ncbschzzt Well-Known Member

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    The pulse is most likely caused by a solenoid sticking which solenoid it is will take some time. Dr. ZX needs to be hooked up and the system checked out, your best bet is to employee your dealer or pay me to fly out to you! Seriously though you need someone to hookup an old Dr.EX or Dr.Zx. Dr.Zx is now available for customers to buy, all you need is the cables and a E2 Palm. Otherwise you are going to be throwing parts at your machine and end up regretting it. The Palm you can get new for $250 or find it on Ebay for less. You can get a complete kit from Deere for about $400, thats the palm, cables, and software. It works on ALL EX machines up to current models.
     
  12. auy_tong2

    auy_tong2 Well-Known Member

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    same problem here
     
  13. -3Doc

    -3Doc Well-Known Member

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    This is normal!! Don't worry about the pulse it is normal for these machines, it is just the pilot pressure relief valve doing its thing. No need to worry.
     
  14. KenAl

    KenAl Well-Known Member

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    Those pulses on that style of machine will increase as the hydraulic oil heats up. The pulses are from the High Speed Solenoids activating to maintain or stroke the pump. If you had test lights on the solenoids you would see the pulses timed with the lights. Perfectly normal on THAT style of machine.
     
  15. auy_tong2

    auy_tong2 Well-Known Member

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    ok thanx..
     
  16. wsw

    wsw Well-Known Member

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    There is no filter bypass valve in the filter head of that machine, look at the regulator first and have a guage installed to read pressure, shim it up till its over 500 psi if it isn't already. do tests with oil warm. how are the controls are they slow or eratic?
     
  17. auy_tong2

    auy_tong2 Well-Known Member

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    still waiting for dr. zx, so i could check pilot pressure =)
     
  18. wsw

    wsw Well-Known Member

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    Yes it has a small accumulator and that definetely could cause the problem