3、 Welding groove type all welded pneumatic ball valve adopts submerged arc automatic welding, and is welded in air cooling or air cooling mode. The wall thickness of the forged steel valve body of the pneumatic ball valve for long-distance pipeline is generally 40~50mm or more, so it is advisable to adopt narrow gap groove submerged arc welding. The bottom gap of the groove is 8~35mm, the groove angle is 1~7, and the number of welds in each layer is 1~3. The process backing plate is often used for backing welding. In order to make the welding wire reach the bottom layer of the narrow slope, a special narrow welding nozzle that can be inserted into the groove shall be designed. The downward extension length of the welding wire is usually 45~75mm to obtain a higher deposition rate. Special flux shall be used for welding, with generally fine particle size, excellent slag removal performance and high strength and toughness weld metal properties. In order to ensure the correct position of welding wire and arc in the deep and narrow groove, automatic tracking control must be adopted when necessary.

Where P1 is the pressure in front of the valve (kPa); KC is the cavitation coefficient. The KC value varies with the type of medium, valve core shape, valve body structure and flow direction. The larger the diameter, the smaller the KC. Generally, KC=0.25~0.65