What is the function of the balance pipe in a multi-stage centrifugal pump?

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The balance pipe of a multi-stage centrifugal pump is a type of balancing method, not a balancing structure; whether it is a balance disc or a balance drum (or a combination of the two), thrust is balanced through this method. What is the function of the balance pipe in multi-stage centrifugal pumps? The function of the balance pipe in a multi-stage centrifugal pump is to lead an external pipe from the outlet seal ring of the pump to its inlet side; this pipe is known as 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 a multi-stage centrifugal pump is in operation, high-pressure water is discharged from the outlet of the impeller; some of this water flows toward the back of the impeller, resulting in a pressure there that is roughly the same as that at the outlet. The side in front of the impeller’s blade passage is the suction side, where the pressure is very low. In this way, a large pressure difference exists on both sides of the impeller, resulting in an axial thrust that points toward the pump inlet and is parallel to the shaft. This thrust presses the entire rotor toward the suction side; in severe cases, it can cause friction or collision between the impeller and the pump casing, affecting the safe operation of the pump. Therefore, it is necessary to find a way to balance this force. There are many ways to balance the axial thrust in multi-stage centrifugal pumps, such as using double-suction impellers or symmetrically arranged impellers (in multi-stage pumps), as well as employing balance holes, balance discs, and balance drums. The balance tube is merely a method for balancing the axial thrust; it directs the pressurized water behind the impeller through the balance tube to the inlet side, thereby balancing the pressures on both sides of the impeller. These methods have a simple structure, but they cannot fully balance the axial thrust; the remaining axial thrust must be absorbed by specially designed thrust bearings.