The impeller of the water pump is a key component of multi-stage centrifugal pumps, made of cast iron. Stainless steel material can also be used, and the blades on the water pump impeller play a major role. The shape and size of the water pump impeller are closely related to the performance of the water pump. Pump impellers can generally be divided into two types: single suction and double suction. Single suction impellers are single-sided suction, while small flow pump impellers are mostly of this type. Double suction impellers are used for both sides of water absorption, and high flow water pumps use double suction impellers.

There are four main forms of multi-stage centrifugal pump impellers: (a) closed type; (b) Front half open; (c) Rear half opening; (d) Open type

1. Closed impeller: composed of blades and front and rear cover plates. Closed impellers have high efficiency and are difficult to manufacture, and are widely used in multi-stage centrifugal pumps. Suitable for conveying clean liquids with low viscosity and no particles, such as water and solutions.

2. Semi open impeller: There are generally two types of structures. One is the front semi open impeller, which is composed of a rear cover plate and blades. This structure has lower efficiency and requires an adjustable gap sealing ring to improve efficiency. The other is the rear semi open impeller, which is composed of a front cover plate and blades. Due to the use of the same sealing ring as the closed water pump impeller, the efficiency is basically the same as that of the closed impeller. In addition to conveying liquid, the blades also have a sealing effect (of the back blade or secondary impeller). A semi open impeller is suitable for conveying liquids containing suspended solids such as solid particles and fibers. The manufacturing difficulty of semi open impellers is relatively low, the cost is low, and the adaptability is strong. In recent years, their application in multi-stage centrifugal pumps for refining and chemical industry has gradually increased, and they are used to transport clear water and liquids similar to clear water.

3. Open type impeller: an impeller with only blades and blade reinforcement ribs, without front and rear cover plates (open type impeller has 2-5 fewer blades). The efficiency of the water pump impeller is low and its application is limited. It is mainly used to transport liquids with high viscosity and slurry like liquids.

The blades of multi-stage centrifugal pump impellers are generally rear curved blades. There are two types of blades: cylindrical and twisted. The application of twisted blades can reduce the load on the blades, improve the suction performance of multi-stage centrifugal pumps, and enhance their resistance to cavitation. However, the manufacturing difficulty and cost are relatively high.

The multi-stage centrifugal pump for oil refining and chemical industry requires the impeller to be a cast or fully welded integral water pump impeller. Welded water pump impellers have been developed in recent years and are commonly used in chemical special multi-stage centrifugal pumps made of metal materials with poor casting performance, such as iron and its alloys. The geometric accuracy and surface smoothness of welded water pump impellers are superior to cast impellers, which is beneficial for improving the efficiency of multi-stage centrifugal pumps.