Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

562 Centrifugal Pumps: Design and Application
clans who specialize in rotating equipment repair. Many plants use independent
repair shops for pump repairs. All of these factors make it increasingly
difficult to assure that the separate seal components are
assembled properly. For these reasons, more and more users are turning
to cartridge seals.
A cartridge seal is a complete seal assembly, including the gland, that
is mounted on a sleeve (see Chapter 17, Figure 17-26). In addition to
being assembled, the seal is also adjusted to the correct operating position.
The user simply slides the cartridge assembly over the shaft and
fastens it in place. This approach is much less prone to assembly and installation
errors.
In the larger plants, used cartridge seals may be reconditioned by a
specialist and stocked for future installation. Smaller plants may rely on
the seal manufacturer to both recondition and stock the cartridge units.
internal Misalignment. Most mechanical seal designs incorporate one
flexible element and one fixed element. The most common arrangement
has the flexible element rotating and the fixed element stationary. Seal
life is greatly improved by assuring that the fixed element is mounted
perpendicular to the rotating shaft. Because the fixed element is contained
in the gland and the gland is bolted to the stuffing box, several
surfaces must be checked for perpendicularity. Furthermore, the shaft is
mounted in the bearing housing that is bolted to the pump case. These
mounting surfaces must also be checked.
For overhung process pumps, a precision dial indicator can be used to
assure that internal misalignment is minimized. The bearing bracket
should be assembled as a complete unit so that the following checks can
be made:
Shaft run-out < 2 mil TIR.
Shaft lift < 3 mil.
Shaft float < 5 mil (this author recommends < 1 mil).
Bracket face square to shaft within 3 mil.
Sleeve (mounted on shaft) run-out < 2 mil.
In addition, the stuffing box face must be checked to ensure that it is
perpendicular to the shaft within 3 mils TIR. The most reassuring
method of checking this is to measure it directly. On some pumps, this
may be done by mounting the assembled bearing bracket to the pump
without including the gland. A dial indicator that reads the stuffing box
face is placed on the shaft. If there is not enough room to do this, an
indirect method must be used. On these pumps, the cover should be
checked to see that the face of the stuffing box and the mounting face for
the bearing bracket are parallel within 3 mils TIR,