There are three main kinds of impellers for centrifugal pump.
1. Closed impeller
It consists of blade as well as front and rear covers. The closed impeller has high efficiency and is difficult to make, and is most widely used in centrifugal pumps. It is suitable for handling clean water and low viscosity fluid without solid particles.
2. Semi-open impeller
It usually has two structures.
One is front semi-open type, which is composed of a rear cover plate and a blade. The structure of the impeller is low in efficiency, and a sealing ring with an adjustable gap is required for improving efficiency.
The other is rear semi-open type, which is composed of a front cover plate and a blade. Since the same seal ring of closed impeller can be used, the efficiency is basically the same and the vanes have a sealing effect (back blade or auxiliary impeller) in addition to the liquid handling.
It is suitable for semi-open impeller to handle liquids with suspended substance such as solid particles and fibers. The semi-open impeller is less difficult to make, has lower cost and is more adaptable. It is gradually used in centrifugal pumps for refining and chemical industry, and is used to transport water and liquid similar with water.
3. Open impeller
Impeller with only vane and its strengthening rib, without front and rear cover is called open impeller, and the number of vanes is between 2 to 5. The impeller has low efficiency and low application, and is mainly used for conveying liquid with high viscosity and slurry liquid.
The vane of the centrifugal pump impeller is generally backward curved. The vane has two kinds of cylindrical and twisted shapes. The application of the twisted vane can reduce its load, improve the suction performance of the centrifugal pump, and enhance the anti-cavitation capability, but it is difficult to make and has a high cost.
The centrifugal pump for refining and chemical industries requires the impeller to be an integral impeller for casting or full weld welding. Welding impeller often used in special centrifugal pumps for chemical industry made of metal materials with poor casting properties (such as iron and iron alloys). The geometric precision and surface finish of the welding impeller are better than the casting impeller, which is beneficial to improve the efficiency of the centrifugal pump.