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  1. #1
    New Member
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    Sep 2009
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    5
    Location
    Decatur, Al
    Tractor
    Kubota L3240

    Default Help for testing a hydraulic cylinder

    How can you check if your cylinders are functioning properly and not bypassing? I seem to have lost a lot of bucket curling strength. If the bucket does not bleed down with a heavy load is that an indicator the cylinders are good, or could it still be bypassing? Another step in my trouble shooting.

    thanks

  2. #2
    Veteran Member
    Join Date
    Apr 2009
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    Location
    Port Angeles WA

    Default Re: Help for testing a hydraulic cylinder

    Quote Originally Posted by Kurtkj1 View Post
    How can you check if your cylinders are functioning properly and not bypassing? I seem to have lost a lot of bucket curling strength. If the bucket does not bleed down with a heavy load is that an indicator the cylinders are good, or could it still be bypassing? Another step in my trouble shooting.

    thanks
    First of all, Is the cylinder of DOUBLE ACTING type? (two hoses to cylinder)

    IF NOT DOUBLE ACTING TYPE (one hose to cylinder), and bucket is beeling down, the CONTROL VALVE is leaking on its own (on the pressurized capped side A port side).

    IF IT IS A DOUBLE ACTING type of cylinder, and bucket is bleeding down, ity is little more complex situation....it can be the same valve leak as above....it can be the piston seal leak over to the rod side, but all that oil will not fit on the rod side, so the volume of the piston rod have to leak out thru the control valve (on the rod side B port or the capped side A port).

    So it can be a few different combinations of problems but allways the control valve have at least a part of the leaks, minimum the rod-volume.

    It is common (normal) that control valve leaks over time when load induced pressure sits on the port. Manufacturer can tell how many cc per minute valve is supposed to leak at a certain pressure. eak data should be available for, P to A and B, A and B to tank, and P to tank if it is a closed center valve. With these normal leaks, it will take many hours for bucket to bleed down in.

    All this concider NO external leaks.

    Note:
    If the actuator have a 1 to 1 ratio, like a hydraulic motor, (or a cylinder with rod on both sides of piston, or two identical cylinders X-connected to each other), load induced pressure can bleed down with motor leak only, but of course also thru valve leak...

  3. #3
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
    Posts
    16,737
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: Help for testing a hydraulic cylinder

    To check for cylinder bypassing, Disconnect both of the lift cylinders rod end from the loader, and support them with a 2 x 4 across the arms. At the valve end, remove the hose going to the the left cylinder rod end , and place in a clean bucket. Start the tractor, and activate the lift lever. Both cylinders will extend. Keep holding the lever for two minutes, and this will force most of the fluid from the rod end of the left cyl. The reliefs might come on. If fluid continues to pour out the cylinder port, there is probably some leakage around the piston o-rings in the cylinder. Do the same thing for the other cylinders. You might have to pressurize the rod end to see if the cylinders are leaking in the retract mode.

    If your cylinders test good. then you can test the valve. With the the loader arms raised, turn off the tractor. If the spools are good and tight, the lift arms will stay raised for a good while, sometimes for weeks. Most don't. What this is checking is whether the spools or barrel of the valve is worn. A good valve will hold a cylinder in place.

    If you had the time and money, you could you could take the cylinders to a hydraulic shop, and they will pressurize the cylinders to test external leakage, internal leakage, which people call bypass. Just one of the cyl leaking will cause loss in power, because the pressure is leaking past the o-rings. The hotter the oil, the worse things will get.

    One clue to cylinder bypassing is, the relief doesn't operate. Why you say, because the pressure is bleeding off past the o-rings. It may be hard to test if both the cyl, and the valve is leaking.
    J.J.

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

    Git er done.

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