Thread Content
The impeller is one of the essential key components in chemical centrifugal pumps; it is through its high-speed rotation that the pump exerts force on the liquid, thereby enabling the transfer of liquid. An impeller generally consists of three parts: blade hubs, and shrouds. There are many ways to classify impellers; here a brief introduction is given to the two classification methods based on structure and shape: Classification by impeller structure 1. Closed impeller – composed of blades along with front and rear cover plates. There are four to six blades between the cover plates. When the bending direction of the blade is opposite to the rotation direction of the impeller, it is called a shield-bent blade. In centrifugal air pumps, the blades of the impeller are generally backward-curving blades. This type of closed impeller has high efficiency and is well suited for transporting clean liquids that contain no solid particles or fibers. This impeller is difficult to manufacture and is most commonly used in chemical centrifugal pumps. 2. Semi-closed impeller: This type of impeller has no cover on the side facing the inlet, but has a cover on the other side; it is suitable for transporting materials that tend to settle or contain particles, and its efficiency is relatively low. A closed impeller features covers on both sides of the blades, offering higher efficiency and being suitable for transporting clean liquids free from impurities. Most centrifugal pump impellers are of this type. 3. Open impeller: This type of impeller has no covers on either side, and its blades are connected to the hub through rib plates. Therefore, it has a simple structure and is easy to manufacture, but its efficiency is low; it is suitable for transporting liquids containing a large amount of solid suspended particles or fibers. Between these two is the semi-open impeller, which has only a rear cover; therefore, it is suitable for transporting liquids that tend to settle or contain suspended solids. Based on the shape of the impeller and the direction in which the fluid flows within it, they can be classified as follows: 1. Radial flow type – In this case, the velocity of the fluid at the inlet, outlet, or both of the impeller is radial. Radial flow impellers are used in chemical centrifugal pumps, where the fluid enters the impeller axially and exits it radially. The energy obtained by the liquid mainly comes from the centrifugal force generated by the rotation of the impeller. 2. Axial flow means that from the inlet to the outlet of the impeller, the velocity of the fluid is primarily in an axial direction. Axial flow impellers are used in axial flow pumps, where the liquid flows axially through the impeller; the energy obtained by the liquid comes primarily from the thrust generated by the rotation of the impeller. 3. The mixed-flow type falls between the two mentioned above, that is, the radial and axial components of the fluid velocity are of the same order of magnitude. Mixed-flow impellers are used in mixed-flow pumps, where the fluid enters the impeller axially and exits in a direction that is somewhere between axial and radial; the fluid is transported by the combined effect of centrifugal force and axial thrust.