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|
| Mechanical
Seal |
| Description: |
Consists of a rotating low friction seal face which attaches
to the shaft and a stationary seal face which mates with the
rotary face. Used for materials down to very fine powder size
or where material head pressure is significant. Supplied with
or without air purge for additional protection.
|
| Advantages:
|
Very
tight seal where even minor loss or contamination can not
be tolerated.
Dynamic
seal in which centrifugal force of the rotating face and high
surface prevent leakage of powder. |
| Limits:
|
More
expensive to overhaul than packing glands (depending on the
application).
Seal
depends on maintaining the absolute “flatness” of
the faces. |
|
|
|
|
Double Lip Seal
|
| Description:
|
Mechanical
spring action maintains contact of seal material to shaft
at two points along shaft. Used for similar applications as
single lip and somewhat finer powders when air purge is added. |
| Advantages:
|
Can apply purge gas between the 2 seals for additional protection
from leakage or contamination.
Provides
redundant protection against potential leakage through seal
either into or out of unit.
Allows higher system pressure or vacuum than single lip
system.
|
| Limits:
|
Same as single lip, plus: Double the points of contact for
failure when compared to a single lip seal.
|
|
 |
|
Single Lip Seal
|
Description: |
Mechanical spring action compresses seal material to shaft
at a single point along shaft. Used for more granular powder
and when there is low or minimal head pressure of finer
materials.
|
| Advantages: |
Automatic
tension on seal by spring mechanism reduces regular maintenance.
Very
inexpensive. |
| Limits: |
Can
not tolerate out of round shafts.
Requires
frequent replacement in dry powder applications.
2
Points of failure possible, spring mechanism and seal material.
Generally,
not good for high pressure.
Subject to “catastrophic” failure.
|
|
 |
|
Standard Packing Gland
|
| Description: |
Multiple strands of materials such as fibers, elastomer,
metals or composite compressed against the shaft between
solid plates. Seals well for material down to fine particle
size or where material head pressure is significant.
|
| Advantages: |
Periodic
tightening maintains seal against leakage and extends time
between overhaul. |
| Limits: |
Periodic maintenance required.
Must be able to remove support collar of end of shaft
to replace.
More
expensive compared to lip seals.
|
|
 |
|
Packing Gland with Lantern Ring
|
| Description: |
Hollow
ring inserted between conventional packing to allow air or
other compressed gas purge. Used when minor loss or contamination
can not be tolerated. |
| Advantages: |
Provides
positive pressure on seal discouraging particles from migrating
along shaft as packing wears or foreign material from entering.
|
| Limits: |
More
costly with respect to packing glands without the ring. |
|
|
|
Split Packing Gland
|
| Description: |
Packing
material is supported in two half-circle collars that are
bolted together. Used to facilitate maintenance on larger
shaft sizes. |
| Advantages: |
Allows
change of the seal assembly without having free end of shaft
or shaft removal. |
| Limits: |
Same
as conventional packing glands. |
|
