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  1. #1
    Machinery_E is offline Stainless
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    Default Axial Piston Hydraulic Pump-Troubleshooting?

    This pump is on the gundrill I'm trying to get going. To start, I'm by no means a hydraulics expert-I sure could use some help here!



    The problem...I don't think the pump is working right. The gage on the left-hand side of the manifold block is only reading about 400 PSI. Its on the output side of the pump. The pump powers two hydraulic cylinders that drive the drill head and also a hydraulic motor that runs the drill head. The cylinders work, IMO slow and rough, but when you open the hydraulic valve to turn on the drill head. (Its mechanical) nothin' happens.

    When the pump is runing it sounds horrible. Its kind of like its hammering...its so loud you about need ear protection!!! This is a axial piston pump as I discovered when I took the end piece apart to see if there was a problem in the pump. It has an adjustable swash plate that's adjusted by loosening a nut, and a clamp that you can see sticking out on the side at the end of the pump. Then you turn what looks to be a rotary union with the hydraulic hose on it to adjust the displacement of the swash plate. When you have it adjusted so the swash plate has no to a very small amount of displacement, the pump sounds fine, but its not making any pressure. When you adjust it all the way in, (and the swash plate is at its max angle) its sounds horrible, and makes the apprx. 400 PSI of pressure according to the gage.

    I'm using what the OEM specs as the correct oil (DTE-24) The tank is full. I pulled the inlet hose off, and you can blow through it fine, and the pickup in the tank (its a screen type deal) looks like its clear. The pump is turning in the right direction. When I had the pump apart it looked okay, nothing looked out of the normal.

    Any ideas of what the problem could be here?

    Thanks so much!!!
    Eric

  2. #2
    HelicalCut is offline Stainless
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    Default

    Running backward would be my first thought otherwise sucking air or blocked suction. How much load is on the motor? I do not know if it is possible for the valve plate to get out of time but if it is then that would also cause the problem described.
    Last edited by HelicalCut; 07-31-2009 at 08:23 PM. Reason: missed something

  3. #3
    mobile_bob is offline Stainless
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    Default

    don't know about your pump, but the ones i see on truck lift units
    that use piston pumps often times have broken springs that keep the pistons back against the swash plate,, when they break the pump looses capacity and enough break you lose pressure and volume
    and the pump will be noisey as hell, and the rams work slowly but jerkily as they try and lift.

    like i said, i don't know if your pump uses springs above the pistons, but it isn't too hard to find out.

    i usually just go to my local bolt/screw supplier and get springs that look close to what i need,, i did it once as a temporary repair while i ordered the correct springs,, after which i found the oem springs looked like 3 rate out of india scrap that i would have been embarrassed to use,, so i didn't use them i left the generic ones in the pump,, they seem to last twice as long as the oem springs

    my theory on the truck pump is the driver throttles up the pto too fast
    trying to make things happen faster, and the speed causes harmonic problems with the springs causing them to fracture and fail prematurely.

    like i said, no idea how your pump works and if it is similar
    fwiw
    bob g

  4. #4
    Machinery_E is offline Stainless
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    HelicalCut, I tried running it the other way and it makes no pressure at all that way, so it must be going the right way. When it makes pressure, it goes in the direction the arrow on the motor says, so we should be good. All the connections are tight on the suction hose and the tank is full, so I can't think how it would be sucking air if it is...

    The valve plate-I'm not sure what that is? Might be my problem!

    Bob, great idea, but this one doesn't use springs. Its got a plate that retains the plungers, and a ball it pivots on in the middle of the plate...

    Thanks guys!

    Eric

  5. #5
    HelicalCut is offline Stainless
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    The valve plate-I'm not sure what that is? Might be my problem!
    The valve plate is the bronze ring with slots in it that the end of the cylinder block bears against, it must be in sync with squash plate so that the pistons are lined up with the suction port when they are extending and lined up with the discharge port when contracting.

  6. #6
    YoungDen is offline Cast Iron
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    Kiron IA USA
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    Default

    Would there be a suction filter in the tank?
    Somtimes, when those pumps go bad, they don't have power to pull the hat off your head. Then, it takes a new rotating group. They have extremely close tolerances. Steel on steel with several thousand pounds oil pressure.

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