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Analysis of the Reasons for the Large Pressure Fluctuation of the Balance Pipe of the Boiler Feed Pump
Sep 15, 2022

The role of the balance pipe of the boiler feed pump:

The balance pipe leads an external pipe from the outlet seal ring of the pump to the inlet end of the pump. This pipe is called the balance pipe. Its main function is to balance the axial thrust of the water pump, reduce the axial movement of the rotor, and prevent friction between the impeller and the casing.

When the boiler feed pump is working, high-pressure liquid is discharged from the outlet of the impeller, and part of it flows to the back of the impeller, so that the pressure behind the impeller is basically the same as that at the outlet, and the front cover of the impeller is the suction end, and the pressure is very low. In this way, the work of the impeller generates a large pressure difference on both sides, which will generate an axial thrust that points to the pump inlet and is parallel to the shaft, so that the entire rotor is pressed to the suction side. The safe operation of the pump must be balanced.

There are many ways to balance the axial thrust, such as using double suction impellers or symmetrically arranged impellers (multi-stage pumps), using balance holes, balance discs, balance drums, etc. The balance tube is just a way to balance the axial thrust. It is to lead the pressure liquid behind the impeller to the inlet side with the balance tube to balance the pressure on both sides of the impeller. This method has a simple structure, but cannot completely balance the axial thrust, and the remaining axial thrust needs to be borne by a specially set thrust bearing and a balancing device.

A simple understanding of the principle of the balance plate is similar to that of the thrust bearing on the steam turbine, and the balance pipe is similar to the oil return pipe of the thrust bearing.

Analysis of the reasons for the pressure fluctuation of the balance pipe of the boiler feed pump:

1. Since it is a balance tube, the pressure of the balance tube should not change too much, or it is blocked or leaked.

2. The balance pipe is used to eliminate the axial thrust. When the pump outlet valve is closed or the back road is blocked, the pressure of the balance pipe is high; when the pump is evacuated, the pressure of the balance pipe is low, and the pressure remains unchanged under normal conditions.

3. The pressure of the balance pipe of the high-pressure feed pump is slightly higher than the inlet pressure. If the pressure increases, it means that the gap between the balance drum and the balance drum sleeve becomes larger. If the pressure reaches 2-3 times the inlet pressure, it is better to disintegrate. check.

4. Due to the serious wear of wearing parts such as sealing rings and balance discs, the pressure of the balance pipe changes greatly.

5. Various inter-stage leakage and frequency conversion of the motor make the pressure difference of the balance tube change (compared with the original speed).

6. When the external inlet pressure changes, the pressure difference of the balance pipe also changes and fluctuates.

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