The so-called auxiliary impeller hydrodynamic seal refers to the installation of an open impeller in a coaxial reverse direction near the back of the impeller rear cover plate of the pump.
When the pump works, the auxiliary impeller rotates with the main shaft of the pump, and the liquid in the auxiliary impeller will also rotate together, and the rotating liquid will produce an outward centrifugal force, which on the one hand withholds the liquid flowing to the mechanical seal and reduces the pressure at the mechanical seal.
On the other hand, prevent the solid particles in the medium from entering the friction pair of the mechanical seal, reduce the wear of the mechanical seal wear block, and extend its service life.
In addition to the sealing effect of the auxiliary impeller, it can also play a role in reducing 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 composed of the addition of the two forces.
It can be seen that in the case of the same performance parameters, the axial force of the submersible pump is larger than that of the general horizontal pump, and the balance difficulty is more difficult than that of the vertical pump.
Therefore, in the submersible pump, the reason why the bearing is easy to damage is also closely related to the large axial force.
If the auxiliary impeller is installed, the direction of the pressure difference force of the liquid acting on the auxiliary impeller is opposite to the combined force of the above two forces, which can offset a part of the axial force, and also play a role in extending the life of the bearing.
However, the use of the auxiliary impeller sealing system also has a disadvantage, that is, a part of the energy is consumed on the auxiliary impeller, generally about 3%, but as long as the design is reasonable, this part of the loss can be reduced to a minimum.
