As a rule of thumb,70% of shaft wear from braided packing is caused by the first and second rings adjacent to the gland follower. Why?
Imagine you had 4 identical full cardboard boxes in a row and pushed on the first one, all 4 boxes would move as one. Packing does not react that way, as compressible braided packing needs to densify sufficiently to push on the next ring and so on.
It is the bottom ring in the stuffing box that needs to be compressed in order to produce an efficient seal. But how can you get the load from the gland follower to this ring?The answer is to use die-formed, or pre-compressed packing rings, allowing the compressive load from the gland follower to move all of the rings equally. The obvious advantage is activating all the rings in the set, including the all important ring that sees the media to be sealed, while reducing overall friction on the shaft/sleeve. Good quality die-formed rings are usually provided as individual sets for each stuffing box, already in the right installation order.
Depending upon the specific
application, size and pressure, these sets may include rings of
various packing types and even spacing rings if required, all to
achieve an optimal and more durable seal.
Other advantages of pre-cut rings vs bulk spools include: Dimensional accuracy and cleanliness, better inventory control, cost savings in labor required to cut and prepare packing rings and ultimately, a longer packing life with reduced shaft wear.
By G. Manning - Senior Technical Advisor
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