Valve is a control component in the fluid transfer system, with functions such as shut-off, regulation, inflow, prevention of backflow, pressure stabilization, diversion or overflow pressure relief. Valves used in fluid control systems, from the simplest shut-off valves to the most complex automatic control systems used in a variety of valves, their varieties and specifications are quite large.
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In the valve design or experience, lift valve packing asbestos packing or graphite packing or PTFE V packing, but these fillers are subject to the limitations of the number of valve opening and closing, that is, with the increase in the number of valve opening and closing, the packing will wear, the gap gradually increased to a certain number of times (according to statistics will not exceed 2000 times) the valve will be leaking from the packing. Leakage will require new packing gland compression. This solution is suitable for the occasion that the valve does not open and close many times.
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If the valve is opened and closed frequently (e.g. 500,000 times a year), this will undoubtedly increase the use and maintenance cost of the valve. Is there a design that can seal the valve after it has been opened and closed 1 to 2 million times? The answer is yes.
One way is to add a gasket under the packing and a spring under the gasket (the preload of the spring needs to be calculated), when the packing wears out, due to the action of the spring, it will re-press the packing and make it sealed. This approach is currently tested through the use of only 50-100 million times to open and close without leakage, the need to use the party in the annual overhaul, re-compression packing gland, only to reduce the usual maintenance.
Another approach is to choose hydraulic, pneumatic sealing technology, change the original valve design ideas, the use of oil cylinder sealing slip ring at the packing, increase the O-ring (need to calculate the friction, sealing pressure, to determine the number of slip ring and O-ring). This approach through the use of, can reach 2 million times to open and close without leakage, but the O-ring to aging, the use of only 5 years, while the cost is higher.