Abstract: A closure for food containers embodying an open-ended resilient tubular elastomeric nipple adapted for connection to a source of vacuum so that air within the container may be evacuated prior to storage of the container and its contents. The nipple is provided with an inner frusto-conical wall of small slant angle which constitutes a valve seat. A spherical ball loosely disposed within the nipple is forcefully drawn against the seat incident to differential air pressure on opposite sides of the ball. Unseating of the ball to equalize the air pressure inside and outside the container is accomplished by pinching the nipple immediately below the ball. An obstruction near the upper rim of the nipple prevents escape of the ball during evacuation of the container or during handling of the closure.