Stem plays a big role as the valve disc and belongs to the main part of valve. It is easily to break down due to the valve frequent closing and opening, and the slide sealing of packing. The packing of lifting valve are mostly asbestos packing, graphite or v type PTFE. But these kind of packing are limited with the opening and closing times. Namely with the added times of valve opening and closing, the packing would be wear, than the gap will be enlarged. With the closing and opening times reaching to a certain amount (not excessive to 2000 times according to the statistics), the leakage would be created from the packing. This is we always calls out leakage. It is required to compress packing gland again after the leakage is caused. This scheme is suitable for very few opening and closing times of valve.  For the valve with frequent opening and closing, the serious situations would be emerged. If the valve is opened and closed between 100,000 to 300,000 times, there is no doubt the use and maintenance costs would be much higher.

 

Valve users then put forward that is there a tight seal when the valve is opened and closed with 1 million to 2 million times. The answer is certain.

 

Here is the answer from China Valmax expert. Add a gasket below the packing. And a spring must be added below the gasket (the preload of spring should be calculated first). When the packing is wear, it should be compressed again after the influence of spring. Then the packing would realize seal. Through the current test, there is no leakage when the closing and opening times of valve are below 0.5 to 1 million times. And compress packing gland again when the users do big repair. This new solution decrease the usual maintenance.

 

Another way is to adopt the hydraulic, pneumatic sealing technology. Change the original design of valve. And use oil cylinder sealing slip ring at the packing place and add an o ring. The friction, seal pressure ratio should be calculated to ensure the amounts of slip ring and o sealing ring. This method can guarantee no leakage when a valve is opened and closed with 2 million times. But it is easily for the o sealing ring to be aging, with a service life of no more than 5 years, while the cost is high.