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  1. #1
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    Default broken pump shaft

    Hello all got a quick question, had a weird thing happen today on one of my tow trucks. We were working the controls and the cylinder hit its limit of throw and I did not release the control imediately ( what I refer to dead heading it) and the whole system quit functioning. Upon investigation we found the shaft broken on the pump yet the pto turns and the pump turns with no problems, any ideas what caused this.

  2. #2
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    Default Re: broken pump shaft

    Relief valve not set right, dirty or broken. Has it been dead heading for awhile?

  3. #3
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    Default Re: broken pump shaft

    no, we were testing it we just put it together how do I check the relief valve or set it to the correct pressure

  4. #4
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    Default Re: broken pump shaft

    You should check with tow truck mfg and see what they say the relief should be set at. It well be set a few psi lower then the pump max psi. You well need a 3000 or 5000 psi gauge to set. Are you sure you have the plumping right, you said just put together. What did you put together, the valve or the system itself ? If the control valve has the relief it well be near the in port on the valve. It welll be set with shims or adjustable spring loaded adjuster.

  5. #5
    Veteran Member David_Kb7uns's Avatar
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    Default Re: broken pump shaft

    Valve plumbed in backwards may render relief unusable and may be cause also.

    David Kb7uns
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  6. #6
    Super Star Member J_J's Avatar
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    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: broken pump shaft

    Quote Originally Posted by Chambless Tow View Post
    no, we were testing it we just put it together how do I check the relief valve or set it to the correct pressure
    Insert the test gage in a tee at the valve in port. It will have shims or adjustable nut that you tighten to raise pressure, or loosen to lower pressure.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  7. #7
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    Default Re: broken pump shaft

    Thank you all will see if we have the flow in the right direction then install a guage, had one of our in house shop mechanics on it and I over saw between calls not sure if he has it correct. Yes, we did build the whole system converted from mechanical hand control to air controled spool valve from a garbage truck we wrecked out. Figured since the truck had air brakes it would be cool to have air controls for the boom, winches,etc. now we just have to work the bugs out. Thankyou again for your help, will keep you advised.

  8. #8
    Super Star Member J_J's Avatar
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    Default Re: broken pump shaft

    You didn't say whether the hyd system is an open or closed system.

    Most hyd valves have the relief valve very close to the in port. So if you find the relief valve, look for a port with a P stamped on it. Some of the other stamped letters are T for tank. BYD/PB for power beyond. Work ports will have A, A1, B, B1, etc.

    Make up a test rig like this or similar and plug it in to a QD, teed into the IN port of the valve..
    Attached Thumbnails Attached Thumbnails -3000-psi-hyd-test-gage   -3000-psi-hyd-test-gage  
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  9. #9
    Veteran Member
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    Default Re: broken pump shaft

    Sounds like you got things going the right way. If something doesn't work out just jump back on here.

  10. #10
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    Default Re: broken pump shaft

    Well I checked the flow and it was going in the correct direction, but I never put a guage on the thing I got frustrated and we got extremly busy. So I had the shop guys put the orignal valve bodies back on the truck, now the boom lift cylinder will raise but not go down. Could this be a ram issue or a holding valve, everything worked fine with the last spool. It worked before but now won't there is fluid movement as we cracked the lines one at a time to check.

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