Due to the pressure difference between the suction and discharge ports, the multistage centrifugal pump is not completely symmetrical to the two sides of the impeller. Vertical multistage centrifugal pump impeller on both sides of the shaft if the liquid pressure regardless of cross-sectional area, also do not consider the impeller rotation effect on pressure distribution, the role of force on the impeller wheel force and wheel cover force difference, difference transformation product and impeller wheel cover area for calculation of the outlet pressure is and because the inlet pressure, outlet pressure is always greater than the inlet pressure, so when the multistage centrifugal pump rotation will have a direction along the axis and the force acting on the rotor entrance.
Unbalanced axial force will increase the operating load of the thrust bearing, the bearing is not good, while the axial force of the pump rotor to the suction port to move, resulting in vibration and may cause the impeller mouth ring friction so that the pump body damage.
For multi-stage centrifugal pump, the general export pressure is much greater than the inlet pressure, so the use of the balance force to eliminate the axial force is particularly important, as to how to eliminate the axial force, see the following two points:
1. Multistage pump is generally used to balance the disc and the impeller of the symmetrical installation, a single pump is generally on the impeller balance hole, of course, in the impeller wheel mounted on the balance of the way to balance the axial force.
2. Although we ask for is to eliminate the axial force, but if the complete elimination of the rotor can also cause instability in the rotation, so when the design will be designed for bearing capacity of 30% to offset, which is why many pump non drive end bearings are usually angular contact bearings, because it can be used under large axial force.
