The purpose of this research is to provide a solution to eliminate the vortices formed upstream of the sliding valve. The effect of the threshold with the geometric shapes of semi-cylinder, cylinder, pyramid and rectangular cube in different widths of 5, 7, 10, 15 and 20 cm under the sliding valve was investigated experimentaly. The results of this research showed that the entry of air into the fluid leads to the formation of the vortex phenomenon in the flow profile due to the water absorption of the slide valve from the surface layers. The conservation of angular momentum at the opening of the valve causes the combination of vertical and horizontal components of the velocity near the sliding valve. The results showed that placing the threshold under the horizontal sliding valve increases the horizontal velocity of the flow. Therefore, it turns the vortex with a larger diameter into end-line vortices. Due to the insignificant effect of threshold shape on vortices, its effect was ignored.
