| 摘要 |
A hydraulic system includes a multi-position valve which controls the flow of system fluid pressure to various work stations. The multi-position valve is biased by a centering spring to a neutral position from which it can be shifted to a selected working position. A retaining mechanism is able to retain the valve in the selected working position when the system pressure is in a prescribed pressure range. The retaining mechanism is urged to its retaining position by a control fluid pressure which is derived from the system pressure. When the system pressure is below or above the prescribed pressure range the retaining mechanism is unable to resist the force of the centering spring and the valve assumes a neutral position. When the system pressure is in the prescribed range, a constant control pressure is supplied to the retaining mechanism for effectively resisting the force of the centering spring. This system assures that upon start-up of a machine in which the hydraulic system is incorporated, the multi-position valve will be in neutral to avoid a hazardous condition.
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