The sealing performance of soft seal is easy to ensure, and the requirements for machining accuracy and surface roughness of sealing surface are not very high. Under the pressure of the medium, the ball moves towards the outlet end and presses the valve seat. At this time, the force QMJ of the ball pressing on the valve seat is: the outer diameter of the valve seat sealing surface, the inner diameter of the valve seat sealing surface. In order to ensure the sealing under low pressure, the pre tightening specific pressure of the pneumatic ball valve and the valve seat must not be less than 1200N • M, and the pre tightening sealing mainly depends on the elasticity of the valve seat itself, Therefore, the width of the sealing surface is limited to a certain extent. The calculation formula is: allowable stress (it is clarified that the allowable stress of fluoroethylene is 1530N. For the valve seat with elastic elements, its working reliability and service life largely depend on the correct selection of the pre compression force of the sealing valve seat.
Under low pressure, under the condition of insufficient preload, the sealing of pneumatic ball valve cannot be guaranteed. The excessive compression will increase the friction torque between the ball and the valve seat, and may cause plastic deformation of the valve seat material.

4. How is China's measurement laws and regulations system constituted? China's measurement supervision system consists of three parts: 1) the measurement methods of the People's Republic of China; 2) the measurement administrative regulations formulated or approved by the State Council and the local measurement regulations formulated by the people's congresses of provinces, cities and autonomous regions. Standing Committee: 3) The metrological management measures and technical specifications formulated by the metrological management department of the State Council, the departmental metrological management measures formulated by the relevant departments of the State Council, and the local metrological management measures formulated by the governmental metrological management department. Above the county level.