The so-called auxiliary impeller hydrodynamic seal means that an open impeller is mounted coaxially opposite to the back of the impeller rear cover of the pump. When the pump is working, the auxiliary impeller rotates with the pump main shaft, and the liquid in the auxiliary impeller rotates together. The rotating liquid generates an outward centrifugal force, which on the one hand bears against the liquid flowing to the mechanical seal, reducing the mechanical force. The pressure at the seal. On the other hand, the solid particles in the medium are prevented from entering the friction pair of the mechanical seal, which reduces the wear of the mechanical seal block and prolongs its service life. In addition to sealing function, the auxiliary impeller can also reduce the axial force. In the submersible sewage pump, the axial force is mainly composed of the differential pressure force of the liquid acting on the impeller and the gravity of the entire rotating part. The direction of action of the two forces is the same, and the resultant force is the sum of the two forces.
It can be seen that in the case of the same performance parameters, the axial force of the submersible sewage pump is larger than that of the general horizontal pump, and the difficulty of balancing is more difficult than that of the vertical pump. Therefore, in the submersible sewage pump, the reason that the bearing is easily damaged is also related to the large axial force. If the auxiliary impeller is installed, the direction of the differential pressure of the liquid acting on the auxiliary impeller is opposite to the resultant force of the above two forces, so that a part of the axial force can be offset, which also plays a role in prolonging the bearing life. However, there is also a disadvantage in using the auxiliary impeller sealing system, that is, a part of the energy is consumed on the auxiliary impeller, which is generally about 3%, but as long as the design is reasonable, the loss can be minimized.