National Mine Service Company

Allen L Jasper

An adjustable jack includes a tubular support member adapted to be positioned vertically on the floor of an entry in an underground mine. An adjusting screw is telescopically positioned within the support member to advance a load bearing plate into engagement with the roof of the mine entry. A nut assembly positioned on the adjusting screw includes a pair of body portions which surround the adjusting screw and are connected to move radially into and out of threaded engagement with the adjusting screw. A retainer secured to the upper end of the tubular support member is arranged to rotatably receive the nut assembly. When the nut assembly is positioned in the retainer, the nut body portions are positioned in threaded engagement with the adjusting screw to permit advancement of the adjusting screw by rotation of the nut assembly. To rapidly advance the adjusting screw to the working height of the jack, the nut assembly is moved upwardly out of the retainer permitting the nut body portions to separate out of threaded engagement with the adjusting screw. The adjusting screw is then free to advance by nonrotational linear movement from the support member through the nut assembly to position the load bearing plate in contact with the mine roof. The nut assembly is returned to the retainer for final adjustment of the jack to exert a preselected compressive force upon the mine roof by rotation of the adjusting screw.

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Morgantown, WV, United States of America

Allen L Jasper