Chemical Engineering September 2014 - 64

Feature Report
it can, and has been, successfully
avoided by the intelligent redesign
depicted in Figure 3.
Using the seal in Figure 3 for new
and existing pumps in hygienic
services allows plant engineers to
avoid substantial risk. This mechanical
seal is not only easier to
clean, but fully harmonizes with
international best practice guidelines.
The design is uncomplicated
and very cost-effective. Most important:
It fits in the space shown
earlier in Figure 1 and represents
true state-of-the-art technology.
Note also that the component
seals in Figures 1 and 2 will require
careful dismantling and reassembly.
In contrast, the recommended
state-of-the-art " slip-in " design of
Figure 3 can be fully assembled
at the factory, which reduces field
work and potential errors. Moreover,
the possibility of process-fluid
contamination is greatly lessened
by incorporating only smoothly contoured
wetted parts. Common sense
convinces us that components with
smooth surface finishes facilitate
cleaning and sterilization. Eliminating
crevices and cavities makes
it much more difficult for microorganisms
and bacteria to adhere
to surfaces. In the state-of-the-art
seal of Figure 3, springs and drive
mechanisms cannot be contacted
by the process fluid.
So, while single-spring component
seals may appear to be lowcost
sealing solutions, they do have
many shortcomings. Best-practices
companies recognize the hidden
costs and contamination risks associated
with outdated designs. Riskaverse
users increasingly make
innovative seal manufacturers
one of their technology resources.
As business partners, both manufacturers
and users demand what
best practices guidelines require.
Not all mechanical seal designs are
the same. Reliability-focused engineers
look at both the " big picture "
and the details of the best available
seal designs.
■
Edited by Gerald Ondrey
Acknowledgement
All three figures courtesy of AESSEAL plc,
(Rotherham, U.K. and Rockford, Tenn.)
Author
Heinz P. Bloch (heinz
pbloch@gmail.com) resides in
Westminster, Colo. His professional
career commenced
in 1962 and included longterm
assignments as Exxon
Chemical's Regional Machinery
Specialist for the U.S.
He has authored over 600
publications, among them 18
comprehensive books on practical
machinery management,
failure analysis, failure avoidance, compressors,
steam turbines, pumps, oil mist lubrication and
practical lubrication for industry. Bloch holds
B.S. and M.S. degrees in mechanical engineering.
He is an ASME Life Fellow and maintains
registration as a Professional Engineer in New
Jersey and Texas.
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64 ChemiCal engineering www.Chemengonline.Com September 2014
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Chemical Engineering September 2014

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