A cover having an exterior crown provided with a hole which is designed to be fixed onto an outer edge of a vat. The cover has a rigid inner capsule for blocking the hole. When the cover is in a final position, the inner capsule which is attached to the crown by a hooked locking device, is elastically engaged. The inner capsule also has a provisional position, in which it is placed in a movable position across the hole, in an inverted position. The cover can be easily removed and placed in its final position by an automatic vat filling installation. The cover is preferably manufactured from a synthetic substance, and has application in the field of conditioning bulk good, such as grains, powders or pastes.