Industrial seal self study guide - SKF.com

Seal Applications (cont.)
An effective solution to separating
two liquids is to install two seals of
same design back to back (fig. 4e).
Sometimes seals are used in
combination to satisfy application
requirements. Here, a V-ring
performs an exclusion function
(fig. 4f).
A variety of factors are used to
determine selection of proper seal
material (fig. 4g).
An alternative, more effective solution is to use two seals of the same
design (CRW1 or CRWH1) installed back-to-back. The sealing lips must
be pointed toward the liquid which they are intended to retain. One lip
should face the lube, while the other faces the fluid (fig. 4e).
To retain a fluid, a spring-loaded seal should be used. If one side will
be occasionally called upon to run in a dry atmosphere, a compatible
grease pack should be used in the cavity between the two seals to
insure sufficient lubrication at all times.
Seals Used in Combination
To satisfy the needs of particularly difficult applications (such as
multiple requirements in one location) or extreme operating conditions,
seals can be used in combination. Such applications might be rolling
mills and power take-off assemblies, where lube retention and
contaminant exclusion are equally critical.
There are several combinations to choose from, depending on specific
application needs. One solution would be to combine opposed CRW or
HDS seals to retain lube and exclude fine contaminants. Another might
be to use a V-Ring to exclude contaminants and protect radial lip seals
for longer life (fig. 4f).
HDS seals used with V-Rings are usually the correct solution
for applications such as roll necks in milling operations.
Factors Determining Seal Material Selection
Choosing the correct seal for an application requires satisfying a
number of operating conditions (fig. 4g). Among these are the
application’s temperature range, lubricant compatibility, chemical
compatibility, shaft speed(s), shaft surface finish, pressure (internal
or external), contaminants to be excluded, housing material/condition,
and abrasion.
Other factors which should be considered are run-out, shaft-to-bore
misalignment, installation/handling, operating torque and, of course,
cost.
Sealing Element (Lip) Materials
Seals are available with a wide variety of sealing element materials.
Selection should be based on sealing application, compatibility with
lubricants and fluids being retained, operation temperatures and
other operating conditions.
Detailed ratings and recommendations for each material can be
found in the first few pages of the SKF Handbook of Seals.
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