| 摘要 |
A soil penetrating tool assembly (10) having a tool shank (18) which is pivotally mounted so as to clear obstructions in the ground. Movement of the shank away from its normal attitude is opposed by a hydraulic ram (22). The force required to be exerted by the shank (18) against the opposing force of the ram (22) is initially high but is reduced upon a predetermined movement of the tool (18) and thus a predetermined retraction of the ram (22). This allows the tool (18) to more easily clear large obstructions without causing damage to the tool (18). Two alternative valving arrangements are disclosed; one internal of the ram (figures 4, 10), where a plug extending in the ram cylinder coacts with a sleeve in the ram plunger, and one external (figure 11) comprising a cam acting on a valve member in a fluid supply line. Hydraulic circuit with pressure amplifier and ram recharge bleed check valve is also disclosed (figures 5-9).
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