Valves are control components in fluid transport systems, with functions such as shut-off, regulation, diversion, prevention of backflow, stabilization, diversion, or overflow pressure relief. Valves used in fluid control systems have a wide variety of varieties and specifications, from the simplest globe valves to various valves used in extremely complex self-control systems.
In valve design or usage experience, the packing of lift valves is mostly asbestos packing, graphite packing, or PTFE V-type packing. However, these types of packing are limited by the number of valve opening and closing times. As the number of valve opening and closing times increases, the packing will wear out and the gap will gradually increase. At a certain number of times (according to statistics, it will not exceed 2000 times), the valve will leak from the packing. After leakage, it is necessary to re tighten the packing gland. This scheme is suitable for situations where the valve opening and closing frequency is not high.
If the valve is opened and closed frequently (such as 500000 times a year), it undoubtedly increases the cost of using and maintaining the valve. Is there a design that can still seal after opening and closing the valve 1-2 million times? The answer is affirmative.
One method is to add a washer under the packing and a spring under the washer (the pre tension force of the spring needs to be calculated). When the packing wears out, the spring will re press the packing to seal it. At present, this method can only achieve no leakage after opening and closing 500000 to 1 million times through usage inspection. The user needs to re tighten the packing gland during annual major repairs, which can only reduce regular maintenance.
Another approach is to use hydraulic and pneumatic sealing technology, change the original valve design concept, use oil cylinder sealing slip rings at the packing, and add O-ring seals (friction force and sealing pressure need to be calculated to determine the number of slip rings and O-ring seals). This method can achieve 2 million times of opening and closing without leakage, but the O-ring seal needs to age and only last for 5 years, and the cost is relatively high.