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Similar Theory of Centrifugal Pumps
Centrifugal pump similar theory 1. Similar conditions ①geometric similarity The two pumps are completely similar in structure, the same size corresponding to the same number of blades, the corresponding angle is equal. ② similar to the movement of two pumps within the corresponding point of the liquid flow is similar, the same size of the speed ratio, the same direction (that is similar to the speed triangle). ③ power similar to the two points within the corresponding pump liquid inertia, viscosity and the same ratio. Meet the above three, two pumps is similar. Usually two pumps as long as meet the geometric similarity and similar movements, it is considered to meet similar conditions. 2. Similar laws similar to the two pumps, you can approximately think of two similar magnetic pump and pump volumetric efficiency, hydraulic efficiency, mechanical efficiency is equal, this has all the following formula, known as the similarity law. Q1, Q2 - pump 1, the flow of pump 2; n1, n2 a - pump l, the pump shaft speed pump 2; D1, D2 - pump 1, pump 2 impeller diameter; Pump 1, pump 2 shaft power; p1, p2 - pump 1, pump 2 conveying medium density. Second, the number of revolutions ns. 1. Define the specific speed ns. Is similar to the theory derived from the quasi-standard, which shows the similar pump flow Q, head H, the relationship between speed n. Similar pumps in similar conditions, the same number of revolutions, but the same pump in different conditions than the number of revolutions ‰ are not equal. Normally only the ns at the best operating point represents a series of geometrically similar pumps. Specific rotation ns. The formula is as follows: Where n - pump shaft speed, r / min; Q a pump rated flow, m3 / s double suction pump and so on; 1 H --- pump rated lift (multi- , That is, H / i, i is the series), m. 2. Type number K is the number of revolutions ns. GB 3216 and ISO 2548, ISO 3555 with the dimensionless number of revolutions, that the number of K said. The unit of each quantity is the same as in formula (2-10). Type number K and our country than the number of revolutions ns. The relationship can be used formula (2-12) said: K = 0.0051759ns (2-12)