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How do I get air out of hydraulic lines?

Discussion in 'Tractor/Loader/Backhoes' started by ddiiggy, Jul 6, 2014.

  1. ddiiggy

    ddiiggy Well-Known Member

    Joined:
    May 23, 2008
    Messages:
    64
    Location:
    MT
    ...or do I worry about it?

    I have replaced hydraulic hoses on machines over the years and have never made any attempt to get air out of the lines.
    I haven't noticed any problems.
    It just seems that air is compressible and could cause mushy action.

    The line that is being replaced goes to a hydraulic cylinder, the fluid doesn't really circulate.
    The fluid just goes one way and then back the other direction.
    There isn't really any exchange going on to make the air all go out.

    Does the air get entrained into the fluid and eventually work its way back to the pump and tank and get out?


    That was my real question for this thread. This next is the cause of my asking:
    Feel free to answer either. I might wish they were separated if these are two completely different subjects.


    I said I haven't noticed any problems... ...before, that I have really been able to pinpoint to air in the lines...
    I do have a Cat416C Loader/Backhoe that I have occasionally had the front bucket maybe act like it had air in line.
    When I have it tipped down trying to pull a pile backwards, sometimes the bucket will flop back up and them sort of flop back down.
    If I cycle it up and back down it will be fine for a while until it happens again. Just occasionally...

    I don't know if this is an indication of air in the lines or if I have a valve that is leaking sometimes.
     
  2. Killbox Alpha

    Killbox Alpha Well-Known Member

    Joined:
    Jul 6, 2014
    Messages:
    85
    Location:
    DFW
    I wouldn't worry about venting the air out. As you operate the cylinder the air will get forced out returning to the hydraulic tank. The only time I've ever been concerned with bleeding the air in a hydraulic system is when it goes directly to a pump or motor. An air pocket in a pump or motor could cause cavitation and or cause the pump to run dry momentarily.

    As far as your Cat bucket question, I don't have much experience with the 416C. I'm sure someone on here will be able to shed some light on it.
     
  3. Deon

    Deon Senior Member

    Joined:
    Jul 25, 2010
    Messages:
    766
    Location:
    Nova Scotia, Canada
    ddiiggy,
    When replacing hoses, just replace the fluid you have lost and carry on. The air will work its way out in minutes. For the floppy loader bucket, my Kubota did it, my Kioti did it and my John Deere does it. I've heard of many machines that do the same so it must be normal at least for some machines.
     
  4. jimg984

    jimg984 Senior Member

    Joined:
    Dec 2, 2009
    Messages:
    507
    Location:
    ronda north carolina
    dumping a heavy loaded bucket to fast,, tilt down faster than the fluid can come in,,causing a floppy bucket, all ways dump slow when heavy loaded
     
  5. JNB

    JNB Senior Member

    Joined:
    Feb 13, 2012
    Messages:
    823
    Occupation:
    Flyin' low and rollin' slow...
    Location:
    North Texas
    The floppy bucket is normal. If you dump fast enough the valve goes into regen. Bumping the joystick to the right will reset pressure so you can pull back on the pile.
     
  6. Jaxo

    Jaxo Member

    Joined:
    Nov 15, 2012
    Messages:
    14
    Occupation:
    Mining
    Location:
    Namibia
    I have JCB 4CX and drained all the oil and replaced it. The pump is noisy. It only goes quiet at very low rpm and moves slow due to low rpm.
    If I increase the rpm or the system is in neutral its noisy again and very poor movement/performance. Maybe air in the pump ?
    How do I fix it..?
     
  7. jimg984

    jimg984 Senior Member

    Joined:
    Dec 2, 2009
    Messages:
    507
    Location:
    ronda north carolina
    sounds like pumps is starving for fluid, not full of fluid, filter clogged up, strainer some where in suction line clogged, a lot of equipt. have a strainer leaving fluid tank, some at the inlet of pump
     
  8. Jaxo

    Jaxo Member

    Joined:
    Nov 15, 2012
    Messages:
    14
    Occupation:
    Mining
    Location:
    Namibia
    Hi Jimg984,
    Thanks man, I took your advise and drained the oil and sure enough one of my guys
    forgot a rag in the pump inlet, before he re-fitted the main pipe from the tank.
    I will start it up tomorrow, but sure it will be fine.

    Thanks
    J