Page 230 - Know and Understand Centrifugal Pumps

Failure Analysis of Mechanical Seals

Figure 14-13

That the mechanic has the drawings available at the moment of
installation. Often times, the engineer stores the drawings in a file
so they won’t get lost or dirty. For innumerable reasons, the
mechanic rarely has a set of drawings available at the installation.

w That the mechanic knows how to interpret engineering schematics.
w That the instructions and schematic are printed in the mechanic’s
native language.

Also the shaft or sleeve should measure the correct dimension within
tolerance, and have the correct surface finish:
w The correct dimension tolerance =: +O.OOO:-0.002 inch. For
example, a 2 inch diameter shaft can measure no greater than 2.000,
and not less than 1.998 inches.
w The surface finish = 32rms, also known by machinists as AAA

Environmental controls for difficult sealing applications

The easiest way to prevent many unplanned premature seal failures is to
use balanced O-ring cartridge designed seals. Most of the seal
manufacturers make models incorporating these design features.
Rarely is a balanced O-ring cartridge seal supplied as standard equip-
ment with a new pump. It’s thought that they cost too much and will
raise the sale price of the pump.
Although the balance feature, O-rings, and the cartridge concept were
discussed in detail in the previous chapter, here is a brief review why this
seal design will give your pumps their best chance for extended leak-
fiee service with reduced maintenance costs.
w Balance - indicates less heat generated. Heat is the principal enemy
of all mechanical seals. There simply is no logical reason for
specifj.ing unbalanced seals.