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  1. #1
    Join Date
    Dec 2008
    North Carolina
    Kubota BX2200

    Default Cross port checks need upstream ported to tank

    I am not a hydraulic expert. But I am what passes for one in our factory. For some reason, the mechanical folks leave the hydraulics to the electrical folks, and the electrical folks are lead by me.

    We have many diverse hydraulic systems, and often there is a cross-port check valve. I have noticed over the years that some of the cross-port check assemblies do not work well. I have tended to assume that it is because of a leak in the piston seal of the cylinder. But that is not an easy assumption to make.

    For one, if the rod seal is not leaking, even if the piston seal is gone, the cylinder simply reverts to a simple ram, and the effective area of the newly created ram is equal to the diameter of the rod, not the piston. Therefore, although the line pressure required to hold the load is greatly increased, the load still should not move, provided rod extension is opposing the load, not rod retraction.

    What I am instead concluding it that cross-port checks are unreliable if the controlling valve blocks ports A and B instead of porting them to tank. This is true even if P is ported to tank.

    Knowing this may effect some of the top and tilt cylinder purchasing decisions.

    Blocking A and B may not render all cross-port checks useless in all instances, but will make many useless.
    Last edited by EE_Bota; 11-20-2010 at 11:47 AM. Reason: Factory, not company.

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