How to balance the axial thrust of water pump
The balance hole should not be too large, which mainly affects the efficiency of the pump. Here are several methods for balancing the axial thrust of the pump.
The balance of axial force of single-stage pump generally has the following forms:
1. Open balance hole
Drill several holes near the hub of the rear cover plate of the pump, and add a sealing ring on the rear cover plate. The outer diameter of the sealing ring is equal to the outer diameter of the impeller suction port. When the pump is working, the liquid in the seal ring of the rear cover plate is connected with the suction port, and the pressure is similar to that of the suction port. The area of the outer rear cover plate of the seal ring is equal to that of the outer front cover plate of the suction port, so the total force of the liquid pressure on the front and rear cover plates is basically equal, and a small part of the unbalanced axial force is borne by the bearing. In general, the effect of balancing axial force by opening balance hole is better. Its characteristics are: there are many leaks, and the liquid passing through the balance hole interferes with the normal flow of the liquid at the impeller inlet, reducing the efficiency of the centrifugal pump by about 2-5%, which is only suitable for small single-stage centrifugal pump.
2. Balance pipe
This method is basically the same as the method of opening the balance hole. The back cover plate of the impeller is provided with an opening ring corresponding to the suction port. The liquid in the sealing space is introduced into the pump inlet by the balance pipe to balance the hydraulic pressure and the inlet pressure, so as to balance the axial force. This device requires that the cross-sectional area of the balance pipe should be equal to or greater than 4-5 times of the cross-sectional area of the ring gap 。
3. Use balance blade
Several radial ribs are symmetrically arranged on the back of the rear cover plate of the impeller. When the impeller rotates, the ribs, like the pump blade, accelerate the rotation of the liquid on the back of the blade, increase the centrifugal force, significantly reduce the pressure on the back of the blade, so that the pressure on both sides of the impeller is balanced. The degree of balance depends on the size of the balance blade and the clearance between the blade and the pump body. The disadvantage is that the pump efficiency is reduced.
4. Double suction impeller
If the impeller with double-sided water inflow is used on the single-stage centrifugal pump with large flow or a few multistage centrifugal pumps, the axial thrust will be balanced by its own working conditions, but in fact, because it is difficult for the manufacturer to make the geometry of the flow passage parts on both sides of the pump completely consistent, there will still be a small axial force acting on the rotor. Therefore, the single row centripetal ball bearing at one end of the pump shaft Suffer.
In addition, for the multi-stage pump axial balancing device, the impeller symmetrical arrangement method, balance hub balance axial force and balance disk balance axial force can be used.