Abstract: A three-plate slide valve closure includes an upper stationary plate fixed beneath an outlet in a liquid melt container, a lower stationary plate positioned at a location spaced from the upper stationary plate, and a slide plate mounted between the upper and lower stationary plates for sliding movement between open and closed positions. The upper stationary plate, the slide plate and the lower stationary plate have extending therethrough first, second and third flow-through openings, respectively, which are aligned when the slide plate is in the open position. At least the upper inlet portion of the third flow-through opening, adjacent the slide plate, has a dimension in the direction of movement of the slide plate which is at least twice as great as the dimension of the second flow-through opening in such direction of movement.