Remotely dismountable valves

A remotely dismountable valve assembly for use with a dangerous fluid circulating pipe disposed within a biological enclosure formed with an opening providing access to said pipe, said assembly comprising a valve body welded to said pipe, said body presenting an upwardly widening truncated seat having a vertical axis, means for precisely positioning said body with respect to said opening with said seat, an upper stop face formed on said valve body, a member presenting an outer lower part of truncated form fitting on said seat, said member having a seal engaging said seat, said member being provided adjacent to the top thereof with a stop surface which abuts the upper stop face of said valve body, a movable obturator, means including a rod extending from said obturator to a location outside said enclosure for controlling the movement of said obturator, a heavy stopper for obturating said enclosure opening, said stopper having an axially extending housing and passage through which said controlling means extends, and a static cross-piece for securing said stopper to said member, said cross-piece having an upper surface cooperating with the lower surface of said stopper.