1. Reduce the transition gap (0.1-0.5mm).
2. Increase the resistance in the leakage channel. However, due to the problems of machining, installation and axial error, the wear between impeller and pump shell is easy to occur. In order to reduce backflow and prolong the service life of the pump shell and impeller, a metal orifice ring is usually embedded on the pump housing or impeller on both sides of the clearance. The contact surface of this mouth ring can be made into a multi-tooth shape, which is used to increase the reflux resistance, reduce the reflux, and improve the effect of reducing reflux, so it is called the mouth ring. This ring is used to withstand wear and tear. Therefore, the service life of the pump housing or impeller can usually be replaced.
Because of the unilateral water intake, the single suction centrifugal pump impeller has only one leakage reducing ring, and the double suction centrifugal pump impeller enters water on both sides. So there are two leak reducing rings. For the is centrifugal pump with large diameter and high head, especially the pipeline centrifugal pump with the balance hole in the back cover of the impeller, there is a leakage reducing ring between the rear wheel disk and the pump shell; for the multi-stage pump, there is a leakage reducing ring at the front and rear of each impeller in order to reduce the leakage of water.