Vortex pump work in the design conditions will not produce radial thrust, because at this time the velocity of the liquid in the volute and the impeller out of the same direction, the liquid into the volute relatively smooth, around the impeller liquid Speed ​​and pressure distribution is uniform. However, when the operating point is lower than the design condition, that is, when the flow rate is small, the velocity of the liquid in the volute is slowed down, but the velocity of the liquid flowing out of the impeller is increased. Because of the small flow rate, The velocity v2m becomes smaller and the circumferential velocity u2 and the displacement angle β2 are constant, so that the outlet flow velocity v2 is leaned forward. As a result, the liquid flowing out of the impeller collides with the liquid in the volute and the kinetic energy is imparted to the vortex The liquid in the shell makes the pressure rise. Liquid from the pump tongue to the diffusion tube in the process of constant impact, the pressure will continue to increase, referring to the pressure distribution curve has become gradually rising shape. When the operating point is greater than the design conditions, the situation is exactly the opposite. At this time, the velocity of flow in the volute becomes larger and the velocity of the flow at the exit of the impeller becomes smaller and tilts backwards. Therefore, the liquid in the volute transfers the energy to the liquid flowing out of the impeller so as to increase the velocity and flow forward. In the process of diffusing the pump tube to the diffuser tube, the volume of fluid in the volute continuously decreases and the pressure distribution becomes smaller and smaller. In addition to the main reasons mentioned above, there are also secondary reasons. Due to the uneven distribution of pressure as mentioned above, the speed at which the liquid flows out of the impeller is different in magnitude. The counter-impact force at this speed acts on the impeller, The role of recoil force. The empirical formula for radial force is: p = 0.36 (1-Q² / Qk²) where HB 2D2γ where p is the radial force in kg Qk is the design flow Q is the actual flow B2 is the total width of the impeller exit, M; D2 - outside diameter of impeller, m; γ - specific gravity, kg / m³, 1000 kg / m³ for water Radial force sometimes large, several times the weight of the rotor, the shaft deflection, wear seal Ring, bushings, so that there will be a serious burning bush, broken shaft accident. Therefore, we must take measures to eliminate.