In valve design or use experience, lift valve packing for asbestos packing ptfe or graphite packing or v-shaped packing, but these packing are subject to the limit the number of the valve opening and closing, is with the increase of valve opening and closing times, packing will wear and clearance increases gradually, to a certain number of times (according to the statistics, but not more than 2000 times) the valve will be leaked from the packing.The packing gland needs to be re-pressed after leakage.This scheme is suitable for valve opening and closing a few occasions.
If the valve is opened and closed frequently (such as 100,000 to 300,000 times a year), this undoubtedly increases the use of the valve, maintenance costs.
Is there a design that allows the valve to be opened and closed one to two million times and still be sealed?The answer is yes.
One option is to add a washer under the packing and a spring under the packing (the pre-load of the spring needs to be calculated). When the packing wears out, the spring will re-compress the packing and seal it.At present, this method can only be used for 500,000 to 1 million times without leakage. It requires the user to re-press the packing gland during the annual overhaul, which can only reduce the usual maintenance.
Another way, is the choice of hydraulic, pneumatic sealing technology, change the original valve design ideas, the use of cylinder seal slip ring in the packing, increase type 0 sealing ring (need to calculate the friction, sealing pressure, to determine the number of type 0 sealing ring).This method through the use, can achieve 2 million times open and close without leakage, but type 0 sealing ring to aging, use time only 5 years, at the same time the cost is high.