A pressure-vacuum cap for a chamber such as an automobile gas tank having a normally upwardly extending filler neck formed with a peripherally and radially extending, upwardly facing sealing surface concentric with the longitudinal axis of the neck, the cap comprising a cover, a concentric housing extending downwardly from the cover into the filler neck and a gasket or gaskets providing a seal between the housing and the sealing surface, the housing providing a valve body having a centrally disposed, concentric passageway extending axially therethrough and in communication with the chamber. A pressure-vacuum valve arrangement is disposed in that passageway for normalizing the pressure in the chamber, venting the chamber to atmosphere when the pressure in the chamber exceeds a predetermined superatmospheric level and when the pressure in the chamber drops below a predetermined subatmospheric level. The valve body also provides, in addition to the pressure-vacuum valve arrangement, a roll-over valve feature. Particularly, the passageway defines a downwardly facing, generally spherical valve seat, and a ball is disposed in the passageway to move against the valve seat to close the passageway against movement of fluid from the chamber when the filler neck is tilted downwardly to a predetermined angle relative to a horizontal plane.
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