In the valve design or use experience, the lifting valve packing is mostly asbestos packing or graphite packing or PTFE V-shaped packing, but these kinds of packing are limited by the number of valve opening and closing, that is, with the increase of valve opening and closing times, the packing will wear out, the gap gradually increases, to a certain number of times (according to statistics will not exceed 2000 times) the valve will leak from the packing. After leakage, the packing gland needs to be re-pressed. This scheme is suitable for occasions where the number of valve openings and closures is not much.

If the valve is opened and closed frequently, (such as 100,000-300,000 times a year), this will undoubtedly increase the use and maintenance costs of the valve.

Is there a design that can seal the valve after 1 million to 2 million openings and closing? 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 is worn, due to the action of the spring, the packing will be re-pressed to make it sealed. This method is currently through the use of inspection, can only achieve 50-1 million times of opening and closing without leakage, the need to use the party in the annual overhaul, re-tighten the packing gland, can only reduce the usual maintenance.

Another method is to choose hydraulic and pneumatic sealing technology, change the original valve design idea, use the cylinder to seal the slip ring at the packing, and add the 0-type sealing ring (you need to calculate the friction and sealing specific pressure to determine the number of slip rings and 0-type sealing rings). By using this method, it can achieve 2 million openings and closures without leakage, but the 0-type sealing ring is aging, the use time is only 5 years, and the cost is high.