3.3 Sealing mechanism of fixed pneumatic ball valve High pressure or pneumatic ball valve with nominal diameter DN ≥ 200mm usually adopts fixed structure. The ball of the fixed pneumatic ball valve does not produce floating amount, which can ensure two-way sealing and reduce the operating torque of the valve; The load fluctuation amplitude on the seal seat is small. Fixed pneumatic ball valves can be divided into ball front sealed (population sealed) and ball rear sealed (outlet sealed) pneumatic ball valves, as shown in Figure 2. Figure 2

2. The type selection of the pneumatic feed water regulating valve for the boiler is poor, which is mainly manifested in 1. The pointer of the boiler feed water pressure gauge keeps swinging, the water supply pressure and water level fluctuate greatly 2. The regulating valve rod keeps moving up and down, causing serious valve rod wear 3. The regulating valve rod is bent due to long regulating time 4. The pneumatic actuator is easy to burn out the motor.