If the impeller is assembled on the shaft correctly, the water ring vacuum pump can have good volumetric efficiency and prevent vibration.
After the impeller is assembled on the shaft, its end face runout must be within the allowable range. The axial clearance between the impeller and the front and rear covers is very small (for example, SZ-1 and SZ-2 are 0.15mm, sz-3 is 0.20mm, SZ-4 is 0.25mm). Excessive end face runout will cause eccentric wear between the impeller and the front and rear covers, which not only makes the pump heat up, increases power consumption, but also increases the end face clearance, increases the leakage of gas through the end face clearance in the compression area, and reduces volume efficiency.
The size of the end face runout depends not only on the shape error of the end face, but also on whether the impeller is correctly assembled on the shaft. For this reason, the assembly shall be carried out with even force, and the shaft hole and shaft shall not be damaged. After the impeller is installed on the shaft, besides the end face runout shall meet the requirements, the imbalance degree of the impeller shall also be checked.
Although the impeller is required to be symmetrically distributed in the design, the center of gravity and the center of rotation are not coincident due to the other defects such as porosity and shrinkage cavity in the casting, and the uneven distribution of the mass in the non machined part during the casting, so that the additional centrifugal force or couple is generated during the rotation of the impeller, resulting in the vibration of the unit.
This kind of vibration is very harmful. It makes the parts in the pump loose and the force acting on the bearing is uneven, thus causing the bearing eccentric wear and premature damage. In addition, if the vibration frequency is equal to the natural vibration frequency of the pump or foundation, resonance will occur, and the water ring vacuum pump unit or foundation will be damaged during resonance. Therefore, it is one of the most important steps in the assembly and repair of water ring vacuum pump to measure and eliminate the unbalanced force of impeller.