Pneumatic ball valve refers to the valve with the ball as the opening and closing part. In western industrial developed countries, the use of pneumatic ball valves is increasing year by year. In China, pneumatic ball valves are widely used in petroleum refining, long-distance pipeline, chemical industry, paper making, pharmacy, water conservancy, power, municipal administration, steel and other industries, and play an important role in the national economy.
1、 Analysis of the causes affecting the sealing performance and service life of pneumatic ball valves Pneumatic ball valves can be divided into floating pneumatic ball valves and fixed pneumatic ball valves according to the ball structure. However, regardless of the type of pneumatic ball valves with ball structures, especially pneumatic ball valves with large diameters, the dead weight of the ball will have an adverse impact on the sealing performance and service life of the valves. For example, the ball of a floating pneumatic ball valve has no lower stem support shaft, so the fitting surface of the seal seat bears the dead weight of the ball. Therefore, under the same working condition, the greater the dead weight of the ball, the greater the wear on the sealing fitting surface of its gravity direction, which greatly reduces the service life of the pneumatic ball valve. At the same time, once the preload between the ball and the seal seat disappears, the greater the mass of the ball, the greater the differential pressure necessary for low-pressure sealing, which greatly reduces the low-pressure sealing performance. Similarly, if the pneumatic ball valve is equipped with a pneumatic drive device for quick opening and closing, its inertia torque will increase several times, dozens of times. Therefore, how to find ways to reduce the dead weight of the ball will have considerable social and economic benefits for the performance, life, inertia torque and manufacturing cost of the product.

Principle of electromagnetic flowmeter 2. Characteristics of electromagnetic flowmeter Electromagnetic flowmeter is not affected by temperature, pressure, viscosity and other external factors, and there is no pressure loss caused by shrinkage or bulge inside the measuring pipe. In addition, the initial signal detected by the flow element is a voltage that changes in an accurate linear manner with the average flow rate of the fluid, and it is independent of other properties of the fluid, It has great advantages. According to the characteristics of sewage, such as large flow change, impurities, low corrosivity, and certain conductivity, electromagnetic flowmeter is a good choice for measuring sewage flow. It has compact structure and small volume. It is easy to install, operate and maintain. The measuring system adopts intelligent design, and the overall sealing is strengthened, so it can work normally in a harsh environment. However, due to technical reasons, it is difficult to enlarge the diameter of vortex flowmeter and its quality. Pipeline ultrasonic flowmeter lacks competitive advantage in price compared with electromagnetic flowmeter. Therefore, in the water and sewage industry, electromagnetic flowmeter, especially large diameter electromagnetic flowmeter, has great advantages and has been widely used.