| 摘要 |
Disclosed is a representative agricultural implement towed by a tractor equipped by a hydraulic power source connected to a lift mechanism for raising and lowering the implement frame so as to vary the ground-working depth of the working tools. The frame carries a sensor responsive to changes in implement depth above and below a preselected norm. This sensor serves as the input for the inventive control valve and system so as to control the implement lift system automatically. The valve is designed as a four-position valve, with one of the positions serving dual modes so that the system produces fast and slow raising, fast and slow lowering and a neutral or balanced position. The valve has a pressure port connected to the pressure side of the tractor source via a manual valve to afford three of the four active positions with one setting of the manual valve. The fourth active position (fast raise) is achieved by changing the manual valve to reverse the pressure and return ports in the depth control valve. Reversal of these ports activates a pressure chamber and pressure-receivable area on the valve spool of the depth control valve.
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