|
Standard shaft
seal designs are not adequate when subjected
to pressures of 10 psi or
higher. As shown in Figure 92,
higher pressures can distort the sealing lip,
resulting in a greater-than-desired amount of
contact between the air
side surface of the lip and the shaft.
Under
some conditions, the pressure will distort the
seal such that the sealing tip leaves the shaft.
This phenomenon, known as bell-mouthing,
generates more friction and heat, and, as a result,
greater wear. This increased wear is evident on
the air side surface of the lip rather than at
the lip contact
point. This greater wear shortens seal life.
In some extreme instances, higher pressures have
even been known to force the seal out of the bore or
to tear the elastomeric lip
away from its metal case.
In
response to the need for seals capable of withstanding
higher pressures, designers have developed a variety
of non-standard designs. These typically feature
heavier-than-normal cross-sections (to minimize
lip distortion) and a greater bonding area
between the lip and the metal case (to lessen the
chances that the lip will be torn away).
Figures
93, 94, 95, 96, and 97 show some
examples of various high pressure shaft seal
designs.
The TCV
seal shown in Figure 93 is
designed for applications up to 50 psi, though
of course the actual pressure limit is influenced
by shaft
speed. The TCV features a flat rubber O.D. and
rubber interior in conjunction with a heavy-duty spring-loaded
primary
sealing lip and a secondary contamination
exclusion lip.
Figure
94 shows a TCN design.
The TCN offers steel lip reinforcement for
added pressure resistance, a heavy-duty spring-loaded
primary sealing lip, a secondary contamination
exclusion lip, and a flat rubber O.D.
The SAV
seal shown in Figure 95 incorporates
a filled PTFE back-up
for increased pressure resistance, a PTFE contamination
exclusion lip, and a steel O.D.
Figure
96 shows the EP2 design.
The EP2 features sealing lips made of PTFE
in order to withstand high pressure, temperatures,
and shaft speeds. The EP2 also boasts a double
reinforced steel case.
The HP1
seal shown in Figure 97 offers
a filled PTFE backup to resist extrusion, a heavy-duty
sealing lip, and a steel O.D. with rubber nose.
NON-STANDARD
DESIGNS MAIN PAGE
|
