causing an air leak. As the pump breaks in, tighten the
gland bolts evenly. The gland should never be drawn
to the point where packing is compressed too tightly,
and no leakage occurs. This causes the packing to burn
the shaft, or shaft sleeve, to be scored, and prevents
liquid from circulating through the stuffing box and
cooling the packing. The stuffing box is improperly
packed or adjusted when friction in the box prevents
the rotating element from being turned by hand. A
packed stuffing box that is operating properly should
run lukewarm with a slow drip of sealing liquid. After
the pump has been in operation for some time and the
packing has been completely run-in, drippage from the
stuffing box should be at least 40 to 60 drops per
minute. This indicates that there is proper packing,
that the shaft sleeve is adequately lubricated, and that it
is cooled properly.
Eccentric operation of the shaft, or shaft
sleeve, through the packing could result in
excess leakage. Correction of this defect is
Packing should be checked frequently and
replaced as service indicates. Six months might be
a reasonable expected life, depending on operating
conditions. It is impossible to furnish an exact
prediction. A packing tool may be used to remove
old packing from the stuffing box. Never reuse old
and lifeless packing or merely add some new rings.
Make sure the stuffing box is thoroughly cleaned
before new packing is installed. Also, check the
condition of the shaft, or shaft sleeve, for possible
scoring or eccentricity, making replacements as
New packing should be placed carefully into the
stuffing box. If molded rings are used, the rings should
be opened sideways and the joints pushed into the
stuffing box first. The rings are installed one at a time,
each ring is seated firmly, and the joints are staggered
so they are not in line. The joints should be kept toward
the upper side of the shaft about a 90-degree angle from
each preceding joint.
If coil packing is used, cut one ring to accurate size
with either a butt or mitered joint. An accurately cut
butt joint is superior to a poor fitting mitered joint. Fit
the ring over the shaft to assure proper length. Then
remove and cut all other rings to the size of this first
sample. When the rings are placed around the
shaft, you should form a tight joint. Place the first
ring in the bottom of the stuffing box. Then
install each succeeding ring, staggering the joints
as described above, making sure each ring is
Make sure the seal cage is properly located in the
stuffing box under the sealing water inlet. The
function of the seal cage is to establish a liquid seal
around the shaft, to prevent leakage of air through the
stuffing box, and to lubricate the packing. If it is not
properly located, it serves no useful purpose.
Mechanical Shaft Seals
A mechanical shaft seal is supplied in place of a
packed stuffing box when specifically requested.
Mechanical seals are preferred over packing on some
applications because they have better sealing qualities
and longer serviceability. Leakage is eliminated when
a seal is properly installed, and normally, the life of the
seal is much greater than that of packing on similar
General instructions for operation of the various
mechanical sealing arrangements are included below.
It is not feasible to include detailed instructions for all
mechanical seals in this chapter because of the almost
unlimited number of possible combinations and
For more information, refer to the
Mechanical seals are precision products and
should be treated with care. Use special care when
handling seals. Clean oil and clean parts are essential
to prevent scratching the finely lapped sealing faces.
Even light surface scratches on these faces could result
in leaky seals. Normally, mechanical seals require no
adjustment or maintenance except routine replacement
of worn or broken parts.
A mechanical seal that has been used should not be
placed back into service until the sealing faces have
been replaced or relapped. (Relapping is generally
economical only in seals that are 2 inches and greater in
Four important rules that should always be
followed for optimum seal life are as follows:
1. Keep the seal faces as clean as possible.
2. Keep the seal as cool as possible.
3. Ensure the seal always has proper lubrication.