The results of measurements of mixing time and pumping capacity for the crystallizer with internal circulation forced by helicoidal agitator placed inside a cylindrical draft tube are presented. The influence of liquid density and viscosity on the circulation intensity was determined. It was found that helicoidal agitators have fine hydraulic properties. The analysis of the relations presented shows that the product of mixing number and pumping capacity number is constant, and depends only on the apparatus volume and agitator diameter. The pumping capacity number is a complex function of the apparatus construction features and the agitator type.