The valve is a control component in the fluid conveying system, which has the functions of shutting off, regulating, diverting, preventing countercurrent, regulating pressure, diverting or overflow pressure relief. Valves for fluid control systems range from the simplest globe valves to valves used in extremely complex automatic control systems in a wide variety of varieties and specifications.
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 types of packing 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 wear, the gap will gradually increase, to a certain number (according to statistics will not exceed 2000 times) the valve will leak from the packing. After leakage, it is necessary to re-press the packing gland. This scheme is suitable for the valve opening and closing times are not many occasions.
If the valve is opened and closed frequently, (such as opening and closing 500,000 times a year), this will undoubtedly increase the use and maintenance costs of the valve. Is there a design that can still seal the valve after opening and closing 1 to 2 million times? The answer is yes.
One way is to add a washer under the packing, add a spring under the washer (the pre-loading force of the spring needs to be calculated), when the packing is worn, due to the action of the spring, it will re-press the packing to make it sealed. At present, this method through the use of the test, can only achieve 500,000-1 million times of opening and closing without leakage, the user needs to re-press the packing cap 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 the cylinder seal slip ring at the packing place, and increase the O-ring seal (need to calculate the friction force and seal pressure, in order to determine the number of slip rings and O-rings). This method can be used to open and close 2 million times without leakage, but the O-ring is aging, the use time is only 5 years, and the cost is higher.
