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  1. #1

    Join Date
    Sep 2004
    Posts
    3
    Tractor
    Ford 1715

    Default Hydraulic problems

    Need pointers on bleeding the hydraulic system.
    After changing a hydraulic pump, filter & fluid on a Long 460 the 3 point keeps bouncing around.
    Any helpful hints???

    Thanks,
    EMail4U

  2. #2
    Elite Member
    Join Date
    Jul 2003
    Posts
    3,373
    Location
    Goffs Corner, KY
    Tractor
    IH 2444

    Default Re: Hydraulic problems

    On my Tractor you just run the lift all the way up and down several times and it self purges and smooths out.

  3. #3

    Default Re: Hydraulic problems

    I get the same response from my JD 310C when I have the engine RPMs cranked. I found that I have to move my bucket with the RPMs at minimum and then crank up the speed when I need the high power to move big rocks or dig hard ground.

  4. #4

    Join Date
    Jan 2004
    Posts
    5,974

    Default Re: Hydraulic problems

    Try running the tractor for a few minutes moving the FEL through all of it's functions and then lower the bucket, run the 3pt up and down, then shut of the tractor with the FEL on the ground and then move the joystick through a few moves.
    Make sure that when you put the loader in float, that it's already on the ground or very near the ground as this can suck up air into the system if you're pushing it into float with the bucket up high.
    If this doesn't change things, you may have a loose connection in all that new work that needs to be addressed. John

  5. #5
    Elite Member
    Join Date
    Jul 2003
    Posts
    3,373
    Location
    Goffs Corner, KY
    Tractor
    IH 2444

    Default Re: Hydraulic problems

    John sez,
    "Make sure that when you put the loader in float, that it's already on the ground or very near the ground as this can suck up air into the system if you're pushing it into float with the bucket up high."

    Is this after you run the hydraulics thru their paces to purge the air or during ?

  6. #6

    Join Date
    Jan 2004
    Posts
    5,974

    Default Re: Hydraulic problems

    </font><font color="blue" class="small">( Is this after you run the hydraulics thru their paces to purge the air or during ?)</font>
    This is anytime the bucket is up in the air, but I really meant in general use, don't float the bucket until it's on or near the ground to avoid getting air in. Sorry, I wasn't very clear on that. John

  7. #7
    Super Member Henro's Avatar
    Join Date
    Jul 2003
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    5,354
    Location
    Few miles north of Pgh, PA
    Tractor
    Kubota B2910, BX2200, Yardman 20HP pos...

    Default Re: Hydraulic problems

    <font color="blue"> Make sure that when you put the loader in float, that it's already on the ground or very near the ground as this can suck up air into the system if you're pushing it into float with the bucket up high. </font>

    I don't claim to be an expert about hydraulic systems by any means, but I have to ask where this air would be coming from.

    In float aren't both sides of the cylinder connected together, so fluid is free tp pass in either direction, somewhat if not totally independent of the pump supply (pressure side)?

    Now I guess if the return to tank entered the tank above the fluid level that might be an opportunity for air to get sucked back if the tractor was turned off and the loader was lowered. My guess though would be that normally the return fluid enters the tank under the surface of the hydraulic fluid in there...

    I've missed the obvious enough to know that I could be missing something here. But at this moment I don't see how putting the loader control valve in float position, with the tractor running or shut down, should introduce air into the system... [img]/forums/images/graemlins/confused.gif[/img]

  8. #8
    Elite Member
    Rest in Peace

    Join Date
    Apr 2003
    Posts
    3,741
    Location
    New Hampshire
    Tractor
    Kubota B2710, IH TD6-62 dozer with Drott 4n1 bucket loader

    Default Re: Hydraulic problems

    Bill,

    I do not think this condition can be caused by placing the FEL into float while raised. I could find no references to this cause in any of my hydraulic publications.

    Here is a description of a similar problem I took from "The Insider Secrets to Hydraulics".

    ==============
    I was recently engaged by a client to conduct failure analysis on a large (and expensive) hydraulic cylinder off an excavator. This hydraulic cylinder had been changed-out due to leaking rod seals after achieving only half of its expected service life.

    Inspection revealed that apart from the rod seals, which had failed as a result of the 'diesel effect', the other parts of the hydraulic cylinder were in serviceable condition.

    The diesel effect occurs in a hydraulic cylinder when air is drawn past the rod seals, mixes with the hydraulic fluid and explodes when pressurized.

    How does this affect a hydraulic cylinder?
    When a double-acting hydraulic cylinder retracts under the weight of its load, the volume of fluid being demanded by the rod side of the cylinder can exceed the volume of fluid being supplied by the pump.

    When this happens, a negative pressure develops in the rod side of the hydraulic cylinder, which usually results in air being drawn into the cylinder past its rod seals. This occurs because most rod seals are designed keep high-pressure fluid in and are not designed to keep air out. The result of this is aeration - the mixing of air with the hydraulic fluid.

    Aeration causes damage through loss of lubrication and overheating, and when a mixture of air and oil is compressed it can explode, damaging the hydraulic cylinder and burning its seals. As you have probably gathered, the term 'diesel effect' is a reference to the combustion process in a diesel engine.

    In the example described above, the cause of the aeration was a faulty 'float' valve. The function of a float valve on a hydraulic excavator is to allow the boom or arm to be lowered rapidly under its own weight.

    When activated, this valve connects the ports of the hydraulic cylinder together allowing it to retract under the weight of the boom or arm. The fluid displaced from the piston side of the cylinder is directed with priority to the rod side, before any excess volume is returned to the hydraulic reservoir. An orifice controls the speed with which the hydraulic cylinder retracts.

    If this valve malfunctions or is set incorrectly, a negative pressure can develop on the rod side of the hydraulic cylinder, causing air to be drawn past the rod seals, leading to failure of the cylinder.

    How can this type of failure be prevented?
    This example highlights the importance of checking the operation and adjustment of circuit protection devices at regular intervals. As in this case, if the faulty float valve had been identified early enough, the failure of this hydraulic cylinder and the significant expense of its repair could have been prevented.
    ==================


  9. #9
    Veteran Member
    Join Date
    Jun 2002
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    1,129
    Location
    Oklahoma City
    Tractor
    Deere 855 (24hp/19@PTO)

    Default Re: Hydraulic problems

    <font color="blue"> to avoid getting air in </font>

    Excluding the type of malfunction described by MR above (which I assume is pretty rare), there should be no air getting in! A cylinder in "float", drifting down, should be pulling hyd. fluid in, not air.

    OkieG

  10. #10

    Join Date
    Jan 2004
    Posts
    5,974

    Default Re: Hydraulic problems

    Maybe it's not supposed to be a problem, but someone had posted a thread about air in the system. Someone else pointed to floating from high up as the cause, and I tried it myself since I had noticed my loader wasn't doing as well as it had originally. After I started only putting into float close to or on the ground, the problem resolved. Works for me for whatever reason.
    As the article Mad posted said, maybe it's a faulty float valve that's adding air when dropping from high up. John

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