Why does the pump shaft move back and forth?
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The axial force of a single-stage centrifugal pump points towards the inlet; then why does it still move in the direction of the motor?
What should be the installation clearance in a diaphragm coupling?
The pressure at the pump outlet should be higher than that at the inlet. Thus, axial play is generated.
Diaphragm couplings are fixed at the factory; all that’s needed is to tighten the coupling screws
It should be moving towards the exit; why is it moving back and forth between the motor and the pump inlet?
Diaphragm couplings have requirements regarding axial clearance; the appropriate values can be found in the **standards
If the size of the rear mouth ring of the impeller is larger than that of the front mouth ring, the axial force may act in the direction of the motor. When the inlet pressure is particularly high, the axial force on the impeller of a single-stage cantilever pump may also act in the direction of the motor. Due to the shaft diameter, only one atmosphere of pressure acts on the motor side
There is no need to go into detail about the generation of axial force; there are various ways to eliminate it. Excessively high inlet pressure, as well as deviations in the clearance between the front and rear ring seals, can cause changes in axial force, leading to movement of the shaft back and forth. This effect is particularly noticeable when the coupling used is a diaphragm coupling. The allowable axial installation error for diaphragm couplings is ±0.4 mm, as specified in the factory documentation for some couplings.
Is it the large number of strands that generates the axial force?
The pump shaft of a single-stage centrifugal pump is usually supported by diagonal contact ball bearings. If play occurs, it indicates that the clearance between the bearing cover and the outer ring is incorrect; if the amount of play is large, leakage from the seal is likely to occur. It is recommended to check the clearance between the bearing cover and the outer ring of the bearing.
The clearance between the bearing cover and the outer ring of the bearing is generally 0.15 mm. The larger the diameter of the rear ring, the smaller the axial force exerted on the impeller in the direction of the motor, rather than greater! ! !