Page 205 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

4. New materials - As soon as a new elastomer compound is
developed, it becomes available and produced in the O-ring form.
Examples are ‘Kalraz’, and ‘Zalak’ produced by Dupont, ‘Mas’
produced by 3M, and ‘Parafluor’ by Parker Hannifin.
5. Reliability - Tolerances to .003 inch assure reliability.
6. Vacuum Service - The O-ring is the only common popular
elastomeric form that seals in both directions.
7. High Pressure - Installed with back-up rings, O-rings are the
standard in high pressure mechanical sealing.
8. Controlled Loading - The grip onto the shaft is determined by the
seal design and the machined groove, and not the mechanic’s
ability to install the seal at the proper dimension and spring
loading.
9. Easy Installation - O-rings slide easily over keyway grooves,
impeller threading and stepped shoulders on sleeves.
10. Less Shaft Wear - Of course O-rings can damage and fret a shaft if
the equipment is misaligned, but it takes much longer than with
other designs.

11. Low Cost - Why pay more?
12. Misalignment - O-rings can compensate for some misalignment in
the seal chamber face and bore better than any other, elastomer
configuration.
13. Impossible to Install Backward.

These pre vious statements refer to designs incorporat
machined yruovn. u-ririyb briuuiu ricver UT UULLCU dydirtbt d bpririy ur cridryru WI~II d
spring load. They lose many of their desirable properties.

The balance effect

Another concept that has become quite popular in industry is the
balanced mechanical seal. Most manufacturers offer seal models
incorporating the balance feature. This balance is not a dynamic
balance, but instead a relationship between the forces tending to open
the faces in a mechanical seal and the forces tending to close the seal
faces (Figure 1 3-8 ) .

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