A closure for a pressure vessel that includes a neck with a groove defined in the inner diameter, and a door assembly that pivots between opened and closed positions. The door assembly includes a door portion sized to be received in an opening of the neck, a guide plate connected to the door portion and rotatable between locked and unlocked positions, a first lock ring segment positioned radially outwardly of the guide plate and a handle. The guide plate includes a first cam path defined therein that receives a cam member of a first lug assembly that extends inwardly from the first lock ring segment. Rotation of the handle (and guide plate) from the unlocked to the locked position moves the first lock ring segment from a locked to an unlocked position. In the locked position, the first lock ring segment is received in the groove of the neck.