| 摘要 |
A hydraulic jarring tool for imparting up-jarring impacts to release a stuck earth boring drill string component is shown. The tool defines upper and lower closed fluid chambers between telescopically moveable concentric cylinders. A fluid metering valve in one fluid passage between the chambers provides limited flow from one chamber to the other and permits telescopic movement at a rate which establishes tension on the drill string and causes the tool to jar. A normally open valve is provided in a by-pass passage between the chambers and is responsive to the fluid velocity therethrough to move to a closed position, restricting fluid flow to pass through the metering valve. However, the tool can be telescopically extended at a somewhat lesser rate insufficient to cause the velocity responsive valve to close thereby permitting the tool to be extended smoothly without a jarring impact.
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