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Stuffing box

sealing

6.1 Shaft sealing

For over a hundred years, the leakage of liquids along the shaft from
the pump casing was minimized by means of an arrangement of
materials, collectively referred to as 'Packing'.
In spite of holding the dubious distinction of being the oldest part of
the design of a modern process pump, packed stuffing boxes are still
widely used owing to a low initial cost, and because their operation is
familiar to plant personnel.

6.2 Packing

Packing is compressed axially into the stuffing box so that it will expand
radially and seal against the bore of the stuffing box and onto the pump
shaft. As there is no relative motion between the packing and the
stuffing box, this function is relatively straight forward. However, with
the friction created by the shaft running on the bore of the packing, a
certain amount of leakage is essential to lubricate and cool the area.

It must therefore be recognized that the function of packing is not to
eliminate leakage from the casing, but rather to restrict the amount of
leakage that will occur to about 40 to 60 drops per minute. In spite of
this, a certain amount of shaft wear is inevitable and therefore standard
practice includes the provision of a protective sleeve over the shaft in
this area.
It is interesting to note that the vast majority of wear on the sleeve is a
result of the outer one or two tings of packing and these can be
relatively easily replaced during a brief shutdown of the pump.

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