Although multiple seals are expensive, difficult to process, and the application and design requirements of medium and high temperature pneumatic ball valves in foreign power plants are limited, they can increase the flow capacity of pneumatic ball valves. The concentric metal ring of this kind of seal is pressed to the ball by pipeline pressure, so as to squeeze the non-metallic seal ring and make the ball form a more tight seal than the metal ring. The high temperature pneumatic ball valve used for throttling abroad is generally l0.5MPa 441 ℃ (825F)+the pressure difference is 3.4MPa. The temperature difference is 243 C (470 F) for valves at 649 ℃ (1200 F) and 32 MPa. The valve body is made of chromium molybdenum alloy, the ball is made of 410 stainless steel, the surface is welded with hard alloy and then plated with chromium, and the seal ring is made of stellite

Preparation before overhaul of tetrafluoro compensator Understand its performance characteristics
Preparation before maintenance of engineering pipeline compensator
1) Prepare all drawings and technical materials, and prepare the construction plan if necessary.
2) Check the quality certificate of the pipeline data and stop the appearance inspection. See Appendix A for selection of common steel pipes.
3) Block the equipment or system for asynchronous maintenance, and add blind plates. The internal purging and replacement of the pipeline are clean, and the construction site conforms to the relevant safety rules.
Dismantling of used pipeline compensator
1) When the operating temperature of the pipeline is higher than 250 ℃ and the temperature drops to 150 ℃, the bolts to be removed shall be poured with mechanical oil or rust inhibitor.
2) The disassembled high-pressure bolts, nuts and reusable gaskets shall be cleaned and inspected one by one.
3) The sealing surface of each part shall be maintained during disassembly, and the open flange of the tetrafluoroethylene compensator shall be sealed for maintenance.
4) The removed pipeline shall be well supported to prevent falling and deformation.
5) For austenitic stainless steel pipes that are likely to suffer from corrosion cracking caused by polysulfuric acid, neutralization cleaning or nitrogen maintenance should be stopped before contacting the atmosphere after disassembly. The recommended neutralization cleaning plan refers to NACE RP0170-97 Protection of Austenitic Stainless Steel and Other Austenitic Alloy Refinery Equipment from Stress Corrosion Cracking Caused by Polysulfuric Acid During Shutdown.