1 impeller and pump body design
The impeller of general impurity pump uses parallel cover plate. After the slurry enters the impeller, an external vortex is formed from the center to both sides at the outlet, resulting in serious wear of the front and rear cover plates and lining of the impeller, which is the main reason for the short service life of the overflow parts. The impeller designed by Werman pump forms a concave shape at the outlet (see Fig. 1 and Fig. 2), so that the speed at the front and rear cover plates on both sides of the impeller is greater than the middle speed. The slurry is divided into two streams of fluid at the outlet and rotates to the center, forcing the particles to flow to the center, resulting in an internal vortex shape, reducing the concentration on both sides, so as to reduce the wear of the flow channel and two side walls of the pump body.
2 submerged pump
The underwater pump is characterized by small land occupation, no shaft seal and no leakage. A typical submerged pump is shown in Figure 3. The pump is equipped with submerged bearing, and the shaft can be designed to be longer. Submerged bearings are usually self lubricated by pumping liquid. When the medium contains solid particles, it will produce abrasion, increase the clearance of the bearing and cause vibration, so it is only suitable for the occasion of conveying clear liquid. When transporting liquid containing solid particles, the service time will be reduced. The reasonable structure is to use two bearings on the pump bottom plate to support and eliminate the underwater bearing. Due to the uneven wear of the impeller and the increase of the imbalance of the rotor, the strength and stiffness of the shaft should be richer and the shaft diameter should be designed coarser. Cantilever submerged pump often adopts rigid shaft. In order to avoid the critical speed of the shaft, the cantilever pump shaft should not be too long, otherwise it needs to be thickened. In addition, the speed of the submerged pump is also low-speed, which is better.
Centrifugal impurity pump mainly has shaft seal types such as packing seal, auxiliary impeller seal and mechanical seal. The smallest advantage of the auxiliary impeller seal is reliable operation, but the inlet pressure of the auxiliary impeller is required to be controlled within a certain range in the design, and the outlet pressure of Werman pump shall be less than 10%. This type of shaft seal does not add shaft seal water, but the use of auxiliary impeller will increase the power consumption, which is generally about 5% of the rated power. The auxiliary impeller must be used together with the parking seal, and the commonly used parking seal is also packing seal.
The packing seal is cheap and reliable, but when transporting the liquid containing solid particles, the shaft seal water must be added for flushing. Generally, the water pressure of shaft seal is equal to the pump outlet pressure plus 35kpa.
Although mechanical seal is a widely used sealing form, some problems are difficult to solve in preventing solid particles from entering the friction pair and the selection of friction pair materials. In most applications, the effect is not ideal.
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