The impeller of the water pump is made of cast iron. The blades on the water pump impeller play a major role, and the shape and size of the water pump impeller are closely related to the performance of the water pump. Water pump impellers can generally be divided into two types: single suction and double suction. Single suction impellers absorb water from one side, while small flow pump impellers are mostly of this type. The double suction impeller absorbs water from both sides, and the high flow water pump impeller adopts the double suction impeller.
classification
There are four main forms of centrifugal pump impeller: closed, front half open, rear half open, and open.
1. Closed impeller: composed of blades and front and rear cover plates. The closed impeller has high efficiency and is difficult to manufacture. Most commonly used in centrifugal pumps. Suitable for conveying clean liquids with low viscosity, such as clear water and solutions, that do not contain particles.
2. Half open impeller: There are generally two types of structures. One is the front half open impeller, which is composed of a rear cover plate and blades. This structure has lower impeller efficiency and requires adjustable clearance sealing rings to improve efficiency. The other is the rear half open impeller, which is composed of a front cover plate and blades. Due to the same sealing ring efficiency that can be applied to closed water pump impellers, and the blades not only transport liquid, but also have the sealing effect of back blades or auxiliary impellers. The semi open impeller is suitable for conveying liquids containing suspended solids such as solid particles and fibers. The manufacturing difficulty of semi open impeller is relatively low, the cost is low, and the adaptability is strong. In recent years, its application in centrifugal pumps for refining and chemical industry has gradually increased, and it is used to transport clean water and liquids similar to clean water.
3. Open impeller: an impeller with only blades and blade reinforcing ribs, without front and rear cover plates. The number of open impeller blades is 2 to 5. The impeller of a water pump has low efficiency and is rarely used, mainly for conveying liquids with high viscosity and slurry like liquids.
The blades of centrifugal pump impellers are generally of the backward curved type. 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 centrifugal pumps, and enhance their resistance to cavitation. However, manufacturing is difficult and the cost is high. The centrifugal pump used in oil refining and chemical engineering 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 mainly used for casting metal materials with poor performance, such as iron and its alloys, and for manufacturing special centrifugal pumps for chemical industry. The geometric accuracy and surface finish of welded water pump impellers are better than those of cast impellers, which is beneficial for improving the efficiency of centrifugal pumps.
Impeller cavitation and protection
The cavitation of the water pump impeller is caused by the vaporization of water, which is the process of water transforming from a liquid state to a vapor state. The vaporization of water is related to temperature and pressure to a certain extent. Under a certain pressure, when the temperature rises to a certain value, water begins to vaporize; If the pressure drops to a certain value at a certain temperature, water will also vaporize, and this pressure is called the vaporization pressure of water at that temperature. If during the flow process, the pressure in a certain local area is equal to or lower than the vaporization pressure corresponding to the water temperature, water vaporizes at that location.
After vaporization occurs, many small bubbles of steam mixed with gas will be formed. When bubbles flow from the low-pressure region to the high-pressure region along with water flow, they rupture under the action of high pressure, and high-pressure water flows at a very high speed to the space occupied by these original bubbles, forming an impact force. The metal surface undergoes severe damage due to fatigue under water hammer pressure. Therefore, we refer to the entire process of bubble formation, development, and rupture leading to material damage as cavitation phenomenon.
After cavitation occurs, traditional repair processes mainly rely on the condition of cavitation for surfacing or repair welding. After repair, the blades are prone to stress deformation and even cracks due to heat concentration. In modern times, polymer composite materials can be used for repair, among which the more mature ones include the Meijiahua technology system. In addition to the material's inherent erosion resistance, its smooth surface not only enhances its ability to resist cavitation, but also improves pump efficiency to a certain extent. The corrosion resistance of the material itself better compensates for the vulnerability of metals to corrosion, avoiding the vicious cycle of metal corrosion and wear, thereby improving the service life of self priming pumps. The use of polymer composite materials can avoid the thermal stress caused by traditional cavitation repair, prevent deformation or even cracks, and effectively protect the damaged self priming pump blades to a large extent.
