Page 228 - Know and Understand Centrifugal Pumps

Failure Analysis of Mechanical Seals

Figure 14-10
-

The shaft frets under the shaft seal

If the mechanical seal is cocked or misaligned onto the shaft (Figure
14-10), or the seal chamber face is not perpendicular to the shaft, the
shaft O-ring will have to flex to maintain face contact. The flexing causes
the shaft seal to rub on the shaft under the seal, which can eat or erode
a groove into the shaft. The pumped fluid can leak under the O-ring, or
the O-ring can hang into the groove and drag the seal faces as the shaft
moves within the bearing tolerance. This is considered a seal problem,
but is actually an alignment problem. There is more information on this
later in this chapter regarding pump reconstruction. Figure 14-11
shows how an O-ring in a misaligned seal can fret the pump shaft.
Aligned
Faces.

\ I
Face
Misalignment.
0

112 Revolution.

The seal rotary face moves to maintain alignment with the stationary face.
The O-ring slides and frets the shaft.
Fiaure 14-11

21 1