| 摘要 |
Hydraulic center and lock structure for the caster wheel of, for example, a tractor-drawn plow, operative on a centering element rigid with the standard of the caster wheel for forcibly centering the standard and ultimately locking the standard against turning about its axis when the caster wheel is in its straight-ahead position. The hydraulic device is bi-directionally operative for disengagement from the centering element to enable free castering of the wheel, as when the plow is raised for transport. The invention also provides two forms hydraulic control for coordinating the raising and lowering of the plow with unlocking and locking the caster wheel. In one form, the system provides for trapping fluid in the caster wheel cylinder in its straight-ahead position, with a separate valve operated manually to release the fluid when the plow is lowered to operating condition. In another form the valve that releases the trapped fluid is made responsive to a predetermined pressure. Both systems prevent unlocking of the caster wheel during relative minor height adjustments of the plow during operation.
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