An automatic hatch assembly for bulk material containers includes a hatch cover which covers a fill opening of the container, and may be retrofitted to existing containers equipped with a conventional hatch cover. A drive unit is operable to open and close the hatch cover, and a locking assembly actuates an extendable lock member. Optionally, a pneumatic seal is provided within the cover for sealing the container from the outside environment. The locking assembly is adapted to resist opening forces applied to the cover, such as when the container is pressurized, and a sequencing controller may be provided to facilitate automated operation of the opening/closing, locking/unlocking, and/or sealing/unsealing of the hatch cover.