3.4 Precompression of seal seat In order to ensure the tightness of pneumatic ball valve when the working pressure of medium is low, a certain preload specific pressure must be formed between the ball and seal seat. In the rigid seal seat, the reliability and service life of the pneumatic ball valve depend on the correct selection of the pre compression amount of the seal seat. The precompression shrinkage is insufficient to ensure the low pressure tightness of the pneumatic ball valve; Excessive pre compression will increase the friction torque between the ball and the seal seat, affecting the action performance of the pneumatic ball valve; And it may cause plastic deformation of the seal seat, leading to seal failure. For PTFE seal seat, its pre tightening specific pressure shall generally be 0.1PN and not less than 1.02MPa. The adjustment of the pre compression amount of the rigid seal seat is realized by changing the thickness of the seal adjusting gasket, and the machining error of the seal adjusting gasket will affect the adjustment effect; Reasonable assembly and adjustment is the key to obtain good sealing performance. In use, after the seal seat is worn, the automatic adjustment ability of preload specific pressure is very poor, so the service life of pneumatic ball valve with rigid seal seat structure is relatively short. One way to solve the problem is to use a seal seat with elastic elements. At this time, the acquisition and adjustment of the pre compression amount is no longer dependent on the sealing adjusting gasket, but is realized by the elastic element. The seal seat with elastic element can not only obtain the necessary pre compression, but also compensate the pre tightening pressure within the elastic deformation range of the elastic element. Therefore, the service life of the pneumatic ball valve is relatively long.

Maintenance of pneumatic ball valve:
1. The pneumatic ball valve shall be stored in a dry and ventilated room, and both ends of the passage must be blocked. The pneumatic ball valve stored for a long time shall be checked regularly to remove the dirt, and the processing surface shall be coated with antirust oil. After the pneumatic ball valve is installed, the equipment shall be inspected regularly. All kinds of pneumatic ball valves in operation shall be complete and intact. Bolts on flanges and supports shall be indispensable, and threads shall be intact without looseness.
2. If the fastening nut on the hand wheel of the pneumatic ball valve actuator is found to be loose, it should be tightened in time to avoid wearing the connection or losing the hand wheel and nameplate. If the hand wheel is lost, it is not allowed to replace it with a monkey wrench, and it should be equipped in time.
3. The packing gland of pneumatic ball valve shall not be skewed or have no pre tightening clearance. For pneumatic valves in the environment prone to rain, snow, dust, sand and other pollutants, their valve stems should be installed with protective covers. The scale on the pneumatic ball valve shall be complete, accurate and clear. The lead seal, cap and pneumatic accessories of the pneumatic ball valve shall be complete and intact. The insulation jacket shall be free from dents and cracks.