Balance Disc

20 Oct 2018Email

The balance disc is mostly used for the segment type multistage pump(we called it conventional pump), which is mounted on the final stage impeller and rotates with the rotor.

The working principal of balance disc as below.

The pressurized liquid coming out of the final stage flows into the cavity in front of the balance disc through the radial gap of the adjustment sleeve, and the cavity is in a high pressure state.

A balance tube is connected to the pump inlet at the back of balance disc, and the pressure is approximately the inlet pressure. The pressure on both sides of the balance disc is not equal, thus creating a backward axial thrust, that is, a balancing force. The balancing force is opposite to the axial force, thus automatically balancing the axial thrust of the impeller.

When the axial thrust of the impeller is greater than the force of the balance disc, the pump rotor moves to the inlet side. Due to inertia, this movement does not immediately stop at the equilibrium position, but to exceed the limit, causing the balance disc axial gap to decrease excessively, so that the leakage amount is reduced, and the pressure in the front cavity of the balance disc is raised.

Then the balance force on the balance disc increases and exceeds the axial thrust of the impeller, pulling the rotor again toward the outlet side. Similarly, this process has inertia, which increases the axial clearance of the balance disc, causes the balance force to be smaller than the axial thrust, and the rotor moves to the inlet side again, repeating the above process.

This process is automatic. When the pump is working, the rotor is always axially swaying at a certain equilibrium position, but the amount of turbulence is extremely small, which is difficult to see from the appearance.

When the balance disc is working, Since the axial thrust causes the pump to sway on the suction side of the water, the balance plate contacts the balance seat and causes wear. In order to reduce wear, the number of starts and stops of the pump should be minimized. In order to increase the wear resistance of the balance disc and the balance seat, strict selection of materials and heat treatment are required to ensure sufficient hardness of the working surface.

When in usage, the return pipe that communicates with the right side of the balance plate must not be blocked. Because there is no pressure difference on both sides of the balance plate, and the balance plate loses the effect of balancing the axial thrust. In daily maintenance, it is necessary to pay attention to dredge the balance plate return water pipeline and check the wear condition of the balance disc and the lower balance seat. If the wear is sever, it should be replaced in time.

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