Page 226 - Know and Understand Centrifugal Pumps

Failure Analysis of Mechanical Seals

Ozone attack
O-rings, especially Buna-N (Nitrile compound), should be stored away
from fluorescent lighting and electric motors. These are sources of
ozone. Ozone causes a general degradation of these elastomers.

Figure 14-7 Nicks and cuts

Nicks and cuts
This failure is mostly evident on start-up as immediate leakage. Extreme
care should be taken to prevent damaging the O-rings as the mechanical
seal is slid down the shaft at installation. The O-ring grips the shaft to
withstand the seal's maximum pressure rating. The O-ring must slide
over the impeller threads, key way grooves, steps on the shaft, and
marks made by previous setscrews. O-rings damage easily.

1
Most pump 1s don't come out ( if service because they break. Most pumps go into the shop
because thl ey're leaking. Ever y day all over the world, too many $2,000.00 mechanical
.
.
seals are thrown into the req de bin or thrown away because of an 110 O-ring.

The elastomer sticks to the shaft

The elastomer or O-ring is seated inside the mechanical seal. It must be
free to move and flex with the seal (Figure 14-8).

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Fiaure 14-8

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