Pneumatic valve valve shaft packing information

1, as the pneumatic valve in the pipeline, usually open/close not frequent, packing in a few years no activity, the packing is not aging, long sealing; 2, packing should also be under the frequent opening and closing valve shaft, sealing good sex; 3, in view of the above requirements, valve shaft packing to do not change; 4, if the packing need to change, should consider to have hydraulic pneumatic valve design conditions change.