The selection of twin screw pump (high temperature twin screw pump and large flow twin screw pump) includes the selection of performance parameters and the selection of pump structure type. For the selection of pump structure, please refer to the introduction of double screw pump structure. 1. flow q: As a positive displacement pump, the main factors affecting the flow of twin screw pump are rotation speed n, pressure p and medium viscosity v.. Influence of rotating speed n of 1. 1: When screw pumps (high-temperature twin-screw pumps and large-flow twin-screw pumps) are working, a sealed cavity is formed between the two screws and the bushing, and a sealed cavity is removed from the inlet to the outlet every time the screws rotate, that is, the liquid with the volume of one sealed cavity is discharged. Ideally, there is no leakage inside the pump, so the flow rate of the pump is proportional to the rotational speed. Namely: qth = n * q.n-speed; Q-theoretical displacement, that is, the volume of liquid discharged by the pump per revolution; Qth- theoretical displacement. 1.2 Influence of pressure p: In the actual working process of twin-screw pumps (high-temperature twin-screw pumps and large-flow twin-screw pumps), there is leakage inside them, which is also called slip. Because there is a certain gap in the sealed cavity of the pump and there is a pressure difference P before and after the sealed cavity, some liquid flows back, that is, there is leakage. The leakage is expressed by q, and Q=Qth- Q is obvious. With the increase of pressure difference P before and after the sealed cavity, the leakage Q gradually increases. For different sections and structures, the influence is also different. Effect of viscosity v of 1.3: Imagine that clear water and viscous paste leak from a funnel-shaped container with the same volume. Obviously, water leaks faster than paste. Similarly, for twin-screw pump, the leakage of high-viscosity fluid is smaller than that of low-viscosity fluid, and the leakage is proportional to the viscosity of the medium. To sum up, it is necessary to comprehensively consider the above factors, and through a series of calculations, we can accurately know whether the actual flow of the pump meets the working conditions. 2. Pressure P: Unlike centrifugal pumps, the working pressure P of twin screw pumps is determined by the outlet load, that is, the outlet resistance. The outlet resistance matches the pump outlet pressure, and the greater the outlet resistance, the greater the working pressure. If you want to know the pressure, you need to use the knowledge of fluid mechanics to accurately calculate the outlet resistance. 3. Shaft power N: The shaft power of twin-screw pump (high-temperature twin-screw pump and large-flow twin-screw pump) is divided into two parts, namely, the nth hydraulic power, that is, the energy of pressure liquid; NR- friction power. For a certain pressure and flow, its hydraulic power is certain, so the factor affecting shaft power is friction rate Nr. Friction power is the part of power consumed due to the friction of moving parts. These friction powers increase obviously with the increase of working pressure difference, and the increase of medium viscosity will also cause the increase of liquid friction power. Therefore, in addition to the hydraulic power, the friction power of the pump also increases with the increase of the viscosity and working pressure of the medium, so the viscosity of the medium is also a very important reference data when selecting the matching motor. Especially when transporting high viscosity media, more accurate calculation is needed. After calculating the power, the relevant regulations stipulated in the sample table should be followed when selecting the matching motor. 4. Calculation and selection of suction performance: The pumps (high-temperature twin-screw pump and large-flow twin-screw pump) work in the following stages: 4. 1 suction, at which time the liquid keeps moving along the suction pipeline; 4.2 The rotating screw transfers energy to the working liquid; 4.3 Extrusion, when the liquid is discharged from the pump with the necessary pressure to overcome all the resistance of the extrusion pipeline system. In the above three stages, the most important stage is to ensure the suction condition of the pump, which is an important condition for the normal operation of the pump, otherwise cavitation will occur, which will cause problems such as vibration and noise. 5. Calculation of cavitation allowance: NPSHr of the pump is related to the rotational speed n, the lead h and the viscosity v of the pump conveying medium. Bornemann twin-screw pump imported from our factory is calculated according to the following formula: npshr = (1.5+0.253vf1.84345+0.0572vf1. N- speed (rpm); Lead content (m); V- working viscosity (e). It can be seen that the NPSHr of the pump increases with the increase of VF and V. Therefore, in the case of poor suction conditions, the twin screw pump with small lead should be selected. This is very important in the choice. 5. 1 Calculation of NPSHa of cavitation allowance of the unit is not detailed here. 5.2 in order to keep the pump working normally, that is, without cavitation and vibration, the following conditions must be guaranteed: NPSHa > NPSHr, which is the suction condition of the pump. 6. Rotation speed selection of twin-screw pumps (high-temperature twin-screw pumps and large-flow twin-screw pumps): Choosing different rotation speeds often involves the following issues: 6. 1 By choosing the appropriate pump rotation speed, you can obtain appropriate performance parameters such as flow rate. 6.2 With the different viscosity, the rotating speed of the pump should also be changed. For Boremann twin screw pump, the change of viscosity is the main condition to determine the speed. The greater the viscosity, the lower the allowable speed. The selection of rotating speed is also a problem of pumping performance, especially in the case of high viscosity. Excessive rotation speed will cause insufficient suction and produce noise and vibration. Therefore, it is necessary to follow the relevant principles to choose the speed. For more information, please consult Depam (Hangzhou) Pump Technology Co., Ltd., thank you!