In the valve design or use experience, the lifting valve packing is mostly asbestos packing or graphite packing or PTFE V-type packing, but these packings are limited by the number of valve opening and closing, that is, with the increase of the number of valve opening and closing, the packing will be worn, the gap will gradually increase, and the valve will leak from the packing to a certain number of times (according to statistics, it will not exceed 2000 times). After a leak, it is necessary to re-compress the packing gland from the source. This solution is suitable for occasions where the number of valve openings and closing is not large.
If the opening and closing times of the valve are frequent, (such as 10-300,000 times a year), this will undoubtedly increase the use and maintenance cost of the valve.
Is there a design that can open and close the valve 1 million to 2 million times and still seal? The answer is yes.
One way is to add a washer under the packing and a spring under the washer (the preload of the spring needs to be calculated), and when the packing wears out, the packing will be re-pressed to make it seal due to the action of the spring. At present, this method can only achieve 50-1 million times of opening and closing without leakage, and the user needs to re-compress the packing gland during the annual overhaul, which can only reduce the usual maintenance.
Another way is to choose hydraulic and pneumatic sealing technology, change the original valve design idea, use cylinder seal slip ring at the packing place, and increase the type 0 sealing ring (the friction force and sealing specific pressure need to be calculated to determine the number of slip rings and type 0 sealing rings). By using this method, it can reach 2 million times of opening and closing without leakage, but the type 0 sealing ring needs to be aged, and the service time is only 5 years, and the cost is high.
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