Isolation valve with frangible flapper element

摘要

An isolation valve that may be inserted in the casing of a subterranean well at a position above a production formation and operated to a closed position upon the withdrawal of the mandrel and wash tube commonly employed for effecting the gravel packing of the screen and production formation. The valve has a frangible flapper piercable by mechanical means or by increased pressure after removal of the wash tube.