May I ask what is the working principle of the balance drum in a multi-stage pump?

The balance drum is a cylinder that is mounted behind the final impeller and rotates along with the shaft; a gap is formed between the outer circular surface of the drum and the casing. In front of the drum is the rear pump chamber of the final impeller, which is connected to the suction inlet at the back. This creates a pressure difference acting on the drum, generating a force opposite to the hydraulic axial force in order to balance it. In fact, the balance drum is just a regular hub structure

A disc placed behind the impeller at the final stage (on the high-pressure side) uses the axial thrust generated by the pressure difference of the gases on its two sides to partially counteract the axial force on the rotor. The pressure on one side of it is roughly the gas pressure (high pressure) in the clearance of the final impeller disk, while the other side is usually connected to the machine’s intake chamber, where the pressure is atmospheric or intake pressure (low pressure). The pressure difference between the two sides mentioned above exerts a force on the rotor that is opposite to the axial force, and the magnitude of this force depends on the area over which the balance disc is under stress. The outer circumference of the balance disc is equipped with a sealing device to maintain a pressure difference in the disc. To prevent the rotor from moving back and forth during operation, it balances only a portion of the axial force, with the remaining axial force being borne by the thrust bearings.

A disc placed behind the impeller at the final stage (on the high-pressure side) uses the axial thrust generated by the pressure difference of the gases on its two sides to partially counteract the axial force on the rotor. The pressure on one side of it is roughly the gas pressure (high pressure) in the clearance of the final impeller disk, while the other side is usually connected to the machine’s intake chamber, where the pressure is atmospheric or intake pressure (low pressure). The pressure difference between the two sides mentioned above exerts a force on the rotor that is opposite to the axial force, and the magnitude of this force depends on the area over which the balance disc is under stress. The outer circumference of the balance disc is equipped with a sealing device to maintain a pressure difference in the disc. To prevent the rotor from moving back and forth during operation, it balances only a portion of the axial force, with the remaining axial force being borne by the thrust bearings

The balance disk is a disk installed in centrifugal compressors behind the final impeller (on the high-pressure side); it uses the axial thrust generated by the pressure difference between the gases on its two sides to partially counteract the axial force on the rotor.

The pressure on one side of it is roughly the gas pressure (high pressure) in the clearance of the final impeller disk, while the other side is usually connected to the machine’s intake chamber, where the pressure is atmospheric or intake pressure (low pressure). The pressure difference between the two sides mentioned above exerts a force on the rotor that is opposite to the axial force, and its magnitude depends on the area over which the balancing disc is under stress. The outer circumference of the balance disc is equipped with a sealing device to maintain a pressure difference in the disc. To prevent the rotor from moving back and forth during operation, it balances only a portion of the axial force, with the remaining axial force being borne by the thrust bearings.

The pressure on one side of it is roughly the gas pressure (high pressure) in the clearance of the final impeller disk, while the other side is usually connected to the machine’s intake chamber, where the pressure is atmospheric or intake pressure (low pressure). The pressure difference between the two sides mentioned above exerts a force on the rotor that is opposite to the axial force, and its magnitude depends on the area over which the balancing disc is under stress. The outer circumference of the balance disc is equipped with a sealing device to maintain a pressure difference in the disc. To prevent the rotor from moving back and forth during operation, it balances only a portion of the axial force, with the remaining axial force being borne by the thrust bearings.

The diagrams provided above show that there are significant differences between the balance discs and balance drums; their working principles also differ, and there are notable differences in their applications as well. Take a look at the diagram; you can search on Baidu for its working principle. I’ll send you a picture. The use of a balance disc device allows all axial forces to be balanced. To ensure that the balance disc can achieve automatic balancing, the support bearings at both ends of the shaft must be able to move axially within a certain range; thrust bearings should not be installed at either end. A balance drum device can only counteract axial thrust and cannot restrict the position of the rotor. When operating conditions change, the rotor may move irregularly, resulting in residual unbalanced forces. Therefore, pumps equipped with balance drums must be fitted with thrust bearings.