| After
considering the factors that generally affect
all O-ring seals, you must also think about your
specific type of application. O-ring seals fall
into two main application categories: static
and dynamic. Static
seals exist where there is no relative motion
between the mating
surfaces being sealed. Both static and dynamic
seals engender their own unique concerns.
Relatively-speaking, however, static seals are
easier to design because they can handle wider tolerances,
rougher surface
finishes, and higher pressure limits. There
are four major types of static seals: STATIC
RADIAL SEALS
Static radial
seals are formed when squeeze (compression)
is applied to the inside diameter (I.D.) and outside
diameter (O.D.) of the O-ring. Cap and plug type
configurations commonly utilize radial seals. An
example of a static radial O-ring seal for a male gland is
shown in Figure 93. A static
radial O-ring seal for a female gland is shown in Figure
94. Gland design measurements for static
radial O-ring seals can be found in Table
41. Gland dimensions can be found in Table
42. STATIC
AXIAL (FACE) SEALS
Static axial
seals (also known as face
seals) are formed when squeeze is applied to
the top and bottom surfaces of the O-ring. Axial
seals are most often used in face (flange)
type designs where an O-ring seats against the groove’s low-pressure
side. A static axial O-ring seal (internal pressure)
is shown in Figure 95.
A static axial O-ring seal (external pressure) is
shown in Figure 96. Gland
design measurements for static axial O-ring seals
can be found in Table 43.
Gland dimensions can be found in Table
44. STATIC
SEALS WITH “DOVETAIL” GROOVES
Dovetails are face type designs that have been customized
to form static seals by structurally immobilizing
the O-ring within the gland. Dovetails are more expensive
and difficult to design and install than the other
types of static seals. A dovetail seal is shown in Figure
97. Gland design measurements for dovetail
grooves can be found in Table 45. STATIC
CRUSH SEALS
Static crush seals use a male cover with a machined
45° angle to “crush” an O-ring into
the corner of a triangular gland. Because the resulting
distortion to the O-ring is permanent, it cannot
be reused later. An example of a static crush seal
is shown in Figure 98.
Gland design measurements for crush seals can be
found in Table 46. STRAIGHT
THREAD TUBE FITTING SEALS
Another
static seal application is the straight thread tube
fitting seal. We will not go into the subject in
detail here because this particular type is not as
common a configuration as the above mentioned seals.
Boss dimensions for industrial straight thread tube
fitting seals can be found in Table 47. The
gland dimensions for the above seals (with the
exception of the tube fitting seal) can be calculated
with our online O-Ring
Calculator. |
