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  1. #1
    New Member
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    Nov 2008
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    Easstern IA
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    New Holland TN75D

    Default purging air from hydraulic lines

    I have finished all new hoses and double-acting cylinder on a FEL snow plow. I will be using my 3rd scv, instead of the third function on my loader. this is on a TN75D with the 810TL loader. My question is, after everything is hooked up, how is the air bled from the lines and the cylinder?

  2. #2
    Veteran Member
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    Feb 2005
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    1,774

    Default Re: purging air from hydraulic lines

    I would just open the valves slowly with low rps and the air will work its way out of the system.
    Hopefully someone else will weigh in here, but I think they will have the same directions too.

  3. #3
    Elite Member ToadHill's Avatar
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    Oct 2005
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    Catt county New York
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    Kioti DK35, Ford 8N, Oliver Cletrac

    Default Re: purging air from hydraulic lines

    I've always just worked the valve slowly un til it operates in a normal manner.
    I can't control my day but I can control my attitude.

  4. #4
    New Member
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    Nov 2008
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    Easstern IA
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    New Holland TN75D

    Default Re: purging air from hydraulic lines

    Thank you. i thought that might be the case, but I always like a second opinion.

  5. #5
    Bronze Member
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    Sep 2006
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    Adelaide, South Australia
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    Kubota B7100D

    Default Re: purging air from hydraulic lines

    Just run the rams to full extension in both directions. As you extend, the other side has no space left and then when you extend that, you get 100% oil. Two cycles and it's done!

    PITA with a backhoe main boom cylinder though - you need to have it parked over a darn big hole so you can extend the arm down. Of course, every workshop has a convenient 6 foot hole in the floor to do this

    /Kevin

  6. #6
    Silver Member
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    Oct 2005
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    182
    Location
    NW Florida, USA
    Tractor
    Kubota L2800 HST

    Default Re: purging air from hydraulic lines

    I'm no expert, but my theory on purging/bleeding is that you don't have to run the cylinder all of the way in or out, you only need to make it stop moving so the pressure will build up. So, as long as a backhoe arm won't lift the tractor, you should be OK as long as it will attain full pressure by stalling.

    As the cylinder pressurizes, the air gets pushed smaller and smaller into very tiny bubbles. After a few cycles, the bubbles all get displaced by oil and make their way back into the tank where they are free to effervesce out of the oil at normal atmospheric pressure.

    Whether that theory is correct or not, the other posters are correct. Just run the cylinder a few times, and it magically starts working!

    - Just Gary

  7. #7
    New Member
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    Nov 2008
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    Easstern IA
    Tractor
    New Holland TN75D

    Default Re: purging air from hydraulic lines

    Thank you one and all. I should have time to try it Monday. I will let you know how it turns out.

  8. #8
    Super Member
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    Sep 2000
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    6,553

    Default Re: purging air from hydraulic lines

    Just use it, no need to be slow Expect some noise in the hydraulic tank as the bubbles hit. You will also need to keep it full. I don't know about the less than full operation, but I suspect that is correct. I know I didn't have full motion with the BH boom and it is air free. By the way, It would need to be a much deeper hole than 6 ft.

  9. #9
    Epic Contributor Soundguy's Avatar
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    Central florida
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    Default Re: purging air from hydraulic lines

    Ditto what the others have said.

    on instalation of large SA cyls wher ei'm using new hose i will usually leave a fitting loose and slowly pressurize the system witht he valve.. then tighten up and just run her all the way up.. then go for it.

    soundguy

  10. #10
    Super Star Member J_J's Avatar
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    JACKSONVILLE, FL
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    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: purging air from hydraulic lines

    I may be wrong on this but, shouldn't the cylinder you are trying to purge be horizontal or level so all the air can be purged. It seems that if you purge with the cylinder in an upright position, you will always have some air trapped, maybe on both ends.
    J.J.

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

    Git er done.

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