1. The structure of electric butterfly valve
. Electric butterfly valve has been inseparable from adjustment since its birth. Because the adjustment characteristic of electric butterfly valve is approximately equal to the percentage, this is one of the reasons that butterfly valve is suitable for adjustment. In addition, the simple structure can be adapted to large caliber. But at a small opening, the butterfly valve has poor regulating performance and is prone to cavitation, erosion, vibration and noise. Therefore, it is generally not allowed to adjust and throttle at a small opening (less than 15°～20°). The flow of the butterfly valve is basically unchanged at 80°～90° close to the fully open position. Therefore it should not be adjusted. The adjustment range of the butterfly valve is generally 20°～70°. The structure of the regulating electric butterfly valve is shown in the figure. It is a pneumatic regulating butterfly valve, and the regulating drive device is a pneumatic diaphragm type. In addition to the pneumatic regulating valve, there are hydraulic or electric. Generally, the valve body structure of the regulating butterfly valve is relatively simple, the valve stem is generally made into the form of a through shaft, and the butterfly plate is generally a flat symmetrical type (I type). In order to reduce the hydrodynamic moment, the butterfly plate is also made into a disc shape, an S shape or a fishtail shape. In order to have a regulating effect at a small opening degree, a sparse tooth valve appeared. Electric butterfly valve is a kind of high pressure recovery electric valve, which is prone to cavitation. When cavitation occurs, behind the contraction site, due to the pressure recovery, the increased pressure compresses the bubbles, and the bubbles that reach the critical size begin to become elliptical, then gradually flatten on the downstream surface, and then burst suddenly. The energy is concentrated on the rupture point, producing a great impact, causing downstream damage. Second, the flow resistance coefficient of the electric butterfly valve If the fluid passes through the valve, the local energy loss caused by the momentum exchange caused by the generation of vortex, deformation, acceleration or deceleration, and the violent collision between the fluid particles causes resistance. 3. The flow rate and flow coefficient of the valve The flow rate of the valve can be obtained by the continuous equation, and then the flow rate can be calculated from the formula (4-1), so the flow rate Q of the valve is the formula C-flow coefficient, which is related to the internal structure of the valve (valve Core valve seat), the pressure difference before and after the valve, fluid properties and other factors are related to the flow capacity of the regulating valve. In the formula, C-flow coefficient, which is related to the internal structure of the valve (spool valve seat), the pressure difference between the front and rear of the valve, and the nature of the fluid. It represents the flow capacity of the regulating valve. Fourth, the selection of electric valve caliber In the general flow calculation process, the flow coefficient of the valve can be divided into the rated flow coefficient and the working condition flow coefficient. The rated flow coefficient is the inherent characteristic of the valve. As long as the valve structure is determined, the rated flow coefficient will be determined accordingly. It has nothing to do with the temperature, pressure, density, etc. of the working condition (see Table 1 for specific values). Working condition flow coefficient, as the name suggests, is determined by the working condition (maximum, normal, minimum) flow and corresponding working temperature, pressure before valve, pressure after valve, medium density and other parameters, and has nothing to do with valve structure. Table 2 The calculation formula of the Kv value of the flow coefficient of the regulating valve. Generally, the selection principle of the electric valve diameter is as follows: ①When the electric butterfly valve is only used as an on-off valve, that is, the state of the valve is either fully open or fully closed. At this time, only the rated flow coefficient of the valve It can be larger than the maximum flow coefficient required by the working condition. The valve diameter is generally the same as the nominal pipe size. ② When the electric butterfly valve is used as a regulating valve, in addition to the rated flow coefficient of the valve being greater than the maximum flow coefficient required by the working condition, it should also be considered that due to the limitation of the valve structure, the butterfly valve has poor adjustment performance at a small opening. Under the minimum operating condition, the valve opening is above 20°, and it is recommended that under the maximum operating condition, the valve opening is below 70°. In order to achieve the effect of throttling regulation, it is generally hoped that the regulation loss of the system should mainly be on the regulating valve, and the flow rate of the butterfly valve can reach about 5m/s. When the butterfly valve meets the above requirements, in many cases the valve diameter needs to be reduced (smaller than the nominal pipe size), but it must not be less than 1/2 of the pipe nominal size. The advantages and disadvantages of the electric butterfly valve: 1. The electric butterfly valve can transport mud, and the accumulation of liquid at the pipe port is the least. 2. A good seal can be completed under low pressure. 3. The electric butterfly valve has good conditioning performance. 4. Opening and closing the lunch box is fast, labor-saving, and low fluid resistance, and can be operated frequently. 5. Simple structure, small size and light weight. The shortcomings of the electric butterfly valve are: 1. The operating pressure and working temperature range are small. 2. Poor airtightness.
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