A centrifugal pump is made up of many parts. According to the working state of each part, it can be roughly divided into three types: rotating parts, fixed parts and handover parts. Take the single stage single suction horizontal centrifugal pump as an example, as shown in Figure 2.4, to introduce the role, composition, structure and materials of each part.
1 Rotating parts
1. Impeller (also known as working wheel)
Impeller is the main parts of the pump, and even the core parts of the pump. Centrifugal pump is to rely on the impeller's high-speed rotation of water to achieve energy conversion.
The impeller of the centrifugal pump is generally composed of two round cover plates. There are a number of curved blades between the cover plates to connect the two cover plates together. The adjacent two blades and the empty tip surrounded by the front and back cover plates are called the flow channel of water.
The shape and size of the impeller is determined by test and calculation, generally can be divided into single suction impeller and double suction impeller. The front cover of the impeller is provided with a single suction impeller, and the front and back cover of the impeller is provided with a round hole.
Figure 2.5 shows the single-suction impeller. The cover plate of the unilateral impeller opens a door to absorb water, while the rear cover plate has no entrance. The front cover plate and rear cover plate of the impeller are asymmetrical. Figure 2.6. It is double suction impeller, the front and rear cover plates of the impeller are provided with circular water intakes, and the front and rear cover plates are in symmetrical shape. It is generally used for large flow centrifugal pumps.
When choosing the impeller material. In addition to considering sufficient mechanical strength, we should also consider the wear resistance and corrosion resistance of the material. At present, most impeller is made of cast iron, cast steel, bronze, hard plastic and alloy steel and other materials also have certain applications.
Impeller can be divided into enclosed impeller, semi-open impeller and open impeller according to its cover plate. As shown in FIG. 2.7, impeller (a) has two front and rear cover plates, which is called enclosed impeller and is most widely used. Single-suction impeller and double-suction impeller belong to this kind of impeller, with more blades in general. There are usually 6 to 8, as many as 12; Impeller (b) only rear cover plate without front cover plate, called semi-open impeller; The impeller (C) does not have complete front and rear covers at all, which is called open impeller. In the delivery of ILI floating sewage pump, in order to avoid blockage, semi-open impeller or open impeller is often used. Its characteristic is the leaf is few, generally only 2 5 pieces.
2. The pump shaft
The pump shaft is used to rotate the pump impeller. It receives power from the prime mover (motor) and drives the impeller to rotate. Therefore, the pump shaft should have enough torsional strength and enough stiffness, the deflection can not exceed the allowable value; Working speed can not be close to the critical speed of resonance phenomenon. Pump shaft commonly used materials are carbon steel and stainless steel.
3. The key
The impeller and pump shaft are connected by keys. Key, commonly known as pin, is the connection of rotating parts. 3 in Figure 2.4 is the flat key usually used in centrifugal pumps. This flat key can only transfer torque but cannot fix the axial position of the
impeller.
