Note: Descriptions are shown in the official language in which they were submitted.
CA 02221477 1997-11-19
MECHANICAL SPLIT DOUBLE SEALS
TECHNICAL FIELD
This invention relates to split mechanical seals and their use.
BACKGROUND
Mechanical seals are designed for use on a wide variety of machines having
rotating
shafts that pass through housings, such as pumps, agitators, blenders,
separators, refiners,
dryers, mixers and other objects. The function of the mechanical seal is to
prevent leakage
of pressurized fluid materials where the shaft passes through the housing. In
the mechanical
seals to which this invention relates -- sometimes referred to as a rotary
face seal -- sealing
is achieved by arranging at least two durable sealing rings having extremely
flat radially
extending sealing faces axially adjacent to each other and concentrically
disposed about the
shaft so that the faces are in sealing contact. One or more rings are held
stationary in the seal
gland while one or more other rings rotate with the shaft as part of a unit
sometimes termed
.a rotary.
Repair or replacement of parts of such seals is difficult whenever
inaccessibility of the
1 S outboard end of the shaft or the location of the machine make it
impossible to slip the seal off
the end of the shaft. In such situations, the machines themselves must be
disassembled. To
facilitate such repair or replacement of parts, use has been made of radially
split seal
assemblies so that the gland, the rotary, and each ring may be removed from
the shaft, and
new rings may be reassembled within the seal and about the shaft. Mechanical
seals of
various designs utilizing split sealing rings are disclosed, for example, in
U.S. Pat. Nos.
2,996,319; 3,101,200; 4,576,384; and G.B. 917,693. In addition, mechanical
seals
employing such split ring technology are available as articles of commerce
from a number
of manufacturers.
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CA 02221477 1997-11-19
Pressurized fluid has been employed to supplement double mechanical seals when
the
material being sealed has particles or other debris suspended therein. In a
typical
configuration, the pressurized fluid is injected into an area between the
seals to create a
positive fluid pressure barrier between the seals and the subject material. In
this way, the
particles or other debris are forced away from the seal ring faces which are
in sealing contact
with and are rotating relative to one another. In the absence of such a
pressurized fluid
barrier, such particles can corrupt the seal between the seal rings, thereby
resulting in damage
to the seal rings and seal leakage. Known mechanical seals employing such
pressurized fluid
use unitary, as opposed to split, configurations. These known mechanical seals
often assume
significant amounts of space axially along the rotary shaft and can prove
difficult to install
and maintain because of their unitary configuration. Thus, a need exists for a
compact,
e~cient mechanical seal which provides the additional benefits of a
pressurized fluid barrier,
while at the same time is easy to install and maintain.
SUMMARY OF THE INVENTION
The present invention is deemed to fulfill this need by providing a novel
mechanical
seal assembly split into at least two assembly sections and constructed such
that, when
assembled, an annular sealed cavity is formed within the assembly to contain
pressurized
fluid, thereby creating a positive fluid pressure barrier across seal faces
within the seal
assembly. Thus, the seal assembly of this invention comprises:
a) at least two split, axially and concentrically aligned stationary seal
rings, each having
a stationary seal face, an inner surface, and an outer surface;
b) a split rotary seal ring rotatable relative to the stationary seal rings
and having a
rotary sealface;
c) a split seal housing encasing the seal rings; and
d) split elastomeric means between the housing and the outer surfaces, and
seal means
between the assembly sections, whereby a sealed annular cavity is formed by
the
housing and the seal rings;
the housing being adapted to admit pressurized fluid into the cavity to create
a positive fluid
pressure barrier across the seal faces when in sealing contact with each
other. The axially
and concentrically aligned stationary seal rings comprise an inner stationary
seal ring and an
outer stationary seal ring, and the area of the axially extending portion of
the outer surface
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CA 02221477 1997-11-19
of the outer seal ring partially defining the annular cavity is greater than
the area of the
axially extending portion of the inner surface of the outer seal ring
partially defining the
annular cavity. In this way, fluid pressure within the annular cavity and
along the outer
surface of the outer seal ring urges the outer seal ring sections together to
provide the
S combined features of split rings and a highly efficient seal.
In preferred embodiments of this invention, the seal assembly is split
substantially
diametrically into a pair of assembly sections. It is also preferred that the
elastomeric means
comprises at least two O-rings, at least one of which is annularly disposed
around one of the
stationary seal rings and at least one of which is annularly disposed around
another of the
stationary seal rings. The seal means preferably comprises a plurality of
gaskets sealing the
split housing when the assembly sections are urged together.
It is also particularly preferred that the outer stationary seal ring be
divided into at
least two outer stationary seal ring segments, each segment further
comprising:
a) two sealing end surfaces, each sealing end surface being co-engageable with
a sealing
end surface of another ring segment to form an interface between that pair of
sealing
end surfaces, the outer surface of the outer stationary seal ring forming a
radially
extending recess traversing the interface, the recess defined in part by a
pair of
spaced-apart parallel radially extended interior wall faces; and
b) an aligning clip projecting from one of each pair of sealing end surfaces
and disposed
between and engaging the interior wall faces of the recess on one side of the
interface
and extendable into the recess on the other side of the interface to maintain
the sealing
end surfaces in detachable co-engagement and alignment with each other.
These aligning clips serve to insure proper alignment of the outer stationary
seal ring
segments when the seal assembly is installed, thereby insuring substantially
leak-free
performance by the outer seal ring.
This invention also provides a method of sealing the annular space between an
object
and a rotatable shaft extending through an aperture in said object. The method
comprises
sealably attaching to the object and around the shaft a mechanical seal
assembly of this
invention.
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These and other embodiments and features of the invention will become still
further
apparent from the ensuing description, accompanying drawings and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts in section (except for the rotary shaft) a preferred seal
assembly of this
invention, partially in phantom view, in which the upper part is taken in one
axial plane and
the lower part in a different axial plane.
Fig. 2 is a plan view of the seal assembly of Fig. 1, partially in phantom
view,
illustrating the cross-section line of Fig. 1.
Fig. 3 is a partially exploded, perspective view of the device of Fig. 1.
Fig. 4 depicts in section the outer stationary seal ring when in sealing
relation with
the housing of a preferred seal assembly of this invention, partially broken
away.
In the Figures, like numerals and reference characters represent like parts
among the
different Figures.
FURTHER DETAILED DESCRIPTION
1 S As stated above, the seal assembly of this invention provides a unique and
beneficial
combination of features in a compact split seal which is easy to install and
maintain on
account of its split configuration and concentric and axially aligned
stationary seal rings.
Referring now to the drawings, Fig. 1 illustrates one section of a split seal
assembly
of this invention. The particular section illustrated in Fig. 1 is identified
in Fig. 2. The seal
assembly section depicted is part of a seal assembly which is split
substantially diametrically,
thus giving this illustration of the assembly section the appearance of a
cross-section of the
seal assembly. Fig. 3 depicts the same seal assembly section in an exploded
perspective
view. As can be seen from Fig. 1, when assembled, the split seal assembly
surrounds a
rotary shaft 1 which extends through an object (not depicted). The seal
assembly comprises
a split inner stationary seal ring 10 and a split outer stationary seal ring
12 which are axially
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CA 02221477 1997-11-19
and concentrically aligned with one another, and which have respective
stationary seal faces
14 and 16, inner surfaces 18 and 20, and outer surfaces 22 and 24. A split
rotary seal ring
26 is rotatable relative to rings 10 and 12, ring 26 having a rotary seal face
28. A split seal
housing, comprised of a split gland 30 and a split rotary 32, substantially
encases seal rings
10, 12 and 26. Although not required, gland 30 of the preferred embodiment
depicted
includes a split spring holder 34 and a split O-ring 36, spring holder 34
partially extending
between seal rings 10 and 12 and being detachably attached to the rest of
gland 30 by a
plurality of annularly disposed bolts 33.
As may be seen in Fig. 1, rotary 32 is substantially surrounded by gland 30,
is
detachably attached to rotary shaft 1 by a plurality of set screws 35 (only
one depicted), and
is placed in sealing relation with rotary shaft 1 by a split O-ring 37. Split
elastomeric means
in the form of split O-rings 38 and 40 are disposed between gland 30 and said
outer surfaces
22 and 24, respectively, and seal means in the form of two gaskets 42 (only
one depicted in
Fig. 1) and two gaskets 43 (only one depicted in Fig. 1) are disposed between
the junctures
of the gland portion and the rotary portion, respectively, of the assembly
sections. A seal is
maintained between rotary 32 and seal ring 26 by a split O-ring 39. When the
seal assembly
has been installed, a sealed annular cavity 44 is formed by gland 30, seal
rings 10, 12, and
26, gaskets 42, and O-rings 36, 38 and 40.
Pressurized fluid may be introduced into cavity 44 through gland 30 via an
inlet
aperture 46, to thereby create a positive fluid pressure barrier across the
seal faces when in
sealing contact with each other. It should be understood that aperture 46 as
depicted with
phantom lines in Figure 1 has been rotated around the rotary shaft for
purposes of illustration
only. Gland 30 further includes an outlet aperture 48, which permits
circulation of fresh
pressurized fluid into cavity 44, thereby serving to transfer heat generated
at points of friction
away from the seal assembly during operation. As can be seen from Figure 2,
apertures 46
and 48 in the preferred embodiment depicted are in fact substantially
diametrically opposite
one another. In addition, outer stationary seal ring 12 includes two notches
47 (only one
depicted on Fig. 1) in its outer surface 24 adjacent to apertures 46 and 48 to
facilitate the flow
of fluid into and/or out of these apertures. While apertures 46 and 48 have
been identified
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CA 02221477 1997-11-19
here as inlet and outlet apertures, respectively, they may alternatively
switch roles to serve
as outlet and inlet apertures, respectively. A plurality of spacers 50 are
also attached to gland
30, preferably at substantially equi-distance from one another, and extending
toward rotary
shaft 1, to thereby maintain the seal assembly in substantially concentric
alignment with shaft
S 1 during installation. As can be seen in Fig. 3, gland 30 has a plurality of
notches 52 at its
perimeter for receiving attachment means (e.g., bolts, screws), for attaching
the seal
assembly to the object through which rotary shaft 1 extends. An O-ring 54 is
also provide
to create a seal between gland 30 and the object to which the seal assembly is
attached.
Seal faces 14 and I6 are maintained in sealing relation with seal face 28 by
biasing
means in the form a plurality of compression springs 56 disposed between
spring holder 34
and either seal ring 10 or 12. A group of compression springs is provided for
each stationary
seal ring, and within each group, the springs are annularly displaced at
substantially equi-
distance from one another so as to provide substantially even axial biasing
force against their
respective stationary seal ring. Inner stationary seal ring 10 is retained to
prevent rotation
with rotary seal ring 26 under operating conditions by a plurality of pins 58
which are affixed
to ring 10, extend through spring holder 34, and are held in place by clips
60. Outer
stationary seal ring 12 is similarly retained to prevent rotation by a
plurality of pins 62 which
are affixed to spring holder 34 and extend into ring 12. Inner ring 10, pins
58, and clips 60
also act to hold outer ring 12 in place through a step 59 along outer surface
22 of inner ring
10 which is configured to meet and abut a step 61 along inner surface 20.
Clips 60 act to
hold rings 10 and 12 in place until the seal is installed.
As previously noted, in preferred embodiments, the area of the axially
extending
portion of outer surface 24 which partially defines cavity 44 is greater than
the area of the
axially extending portion of inner surface 20 which partially defines cavity
44. Thus, as may
be seen in Figure 4, inner surface 20 further includes inner surface portions
20a, 20b, 20c,
21 and 23. The area of outer surface 24 which extends the length of a and
partially defines
cavity 44 should be greater than the area of portions 20a, 20b, and 20c of
inner surface 20.
The length a is defined as the distance from the end of outer ring 12 opposite
seal face 16 to
the initial point of sealing contact between O-ring 40 and outer surface 24.
In most if not all
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CA 02221477 2001-03-26
cases, this point of initial sealing contact will be at or to the right of the
center line of O-ring
40, as depicted in Figure 4. Inner surface portions 21 and 23 are not
considered in this
calculation, since force applied to these portions by fluid pressure does not
substantially affect
the radial position of the sections of outer ring 12. 'this preferred
embodiment provides a way
for fluid pressure within cavity 44 to positively act against outer surface 24
to urge the sections
of outer seal ring 12 together, thereby providing a very efficient seal.
It will be understood that, in the device of this invention, outer seal ring
12 is divided
into at least two outer stationary seal ring segments, only one of which is
depicted in Figs. 1
and 3. As depicted in Fig. 3, each outer stationary sealing ring segment in
preferred
embodiments comprises two sealing end surfaces 64 and 66, each sealing end
surface being
co-engageable with a sealing end surface of another segment (not shown) to
form an interface
between that pair of sealing end surfaces, outer surface 24 forming a radially
extending recess
68 traversing the interface. Recess 68 is defined in part by a pair of spaced-
apart parallel
radially extended interior wall faces 70 and 72. An aligning clip 74 projects
from one of each
pair of said sealing end surfaces and is disposed between and engages interior
wall faces 70
and 72 of recess 68 on one side of the interface to be extendable into recess
68 on the other
side of the interface, thereby maintaining sealing end surfaces 64 and 66 in
detachable co-
engagement with the respective sealing end surfaces of the other segment.
These aligning clips
are described in greater detail in Applicant's U.S. Patent 5,615,893.
It may be seen from Figs 1 and 3 that both gland 30 and rotary 32 have a
plurality of
apertures 76 and 78, respectively, and a plurality of threaded holes 80 and
82, respectively, for
receiving attachment means, such as bolts or screws, for attaching the rotary
sections together
and the gland sections together during assembly. Two bushings 84 and 86 are
also provided
on gland 30 and rotary 32, respectively, to be received by counterparts to
apertures 88 and 90,
respectively, to properly align the gland sections and the rotary sections
during installation of
the seal assembly.
7
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CA 02221477 1997-11-19
The gland and rotary components of the housing of this invention may be
fabricated
from a variety of materials, including stainless steel, brass, other metal
alloys and resilient
plastics. Preferred materials include 316 stainless steel for the gland and
the rotary. The
biasing means typically used in the practice of this invention will be a
plurality of
compression springs retained so as to have an axis which is parallel to the
rotary shaft axis,
although a variety of alternative biasing means may be employed, including,
for example,
canted coils, wave springs, leaf springs, and bands of resilient copolymers.
Again, when
compression springs are used, the springs may be fabricated from an number of
resilient
materials, with Hastelloy~ C-276 being particularly preferred for its
corrosion-resistant
properties. The elastomeric means employed in the device may be O-rings, box
strips, or
other suitable elastomeric materials which can provide a seal. However,
conventional O-
rings fabricated with standard rubber compositions are preferred. The seal
means employed
in the device may be elastomeric gaskets, silicon strips, plastic, or any
other suitable resilient
materials which can provide a seal at the splits in the seal assembly housing.
Again,
conventional elastomeric gaskets fabricated with standard rubber compositions
are preferred.
The retainer pins, screws and bolts utilized in preferred embodiments also may
be fabricated
from a variety of materials, including stainless steel, brass, other metal
alloys and resilient
plastics. The number of screws, bolts, pins and clips used may vary depending
upon the
shaft diameter. With regard to each component of this device, the particular
material used
to fabricate a particular component may vary depending upon the use to which
the device will
be put.
In particularly preferred embodiments for shaft diameters of from about 1 to
about 8
inches, the outer stationary seal ring preferably is fabricated from carbon or
silicon carbide,
while the other stationary seal rings preferably are fabricated from resin-
impregnated carbon.
The rotary seal ring of the device is preferably fabricated from silicon
carbide as well. In this
way, the stationary seal faces are composed entirely of carbon or silicon
carbide materials,
thereby producing a minimal amount of friction-generated heat and durable wear
surfaces
which maintain their original flat surface characteristics, even if abrasives
from the material
sealed manage to enter space between the seal faces.
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As one might expect, the various embodiments of this invention may be
fabricated using
a variety of dimensions and materials, depending in large part upon the size
of a particular shaft
and bearing housing aperture with which the device will be used.
This invention is susceptible to considerable variation in its practice.
Therefore the
foregoing description is not intended to limit, and should not be construed as
limiting, the
invention to the particular forms of the invention described with reference to
the Drawings or
Examples. Rather, what is intended to be covered is as set forth in the
ensuing claims and the
equivalents thereof permitted as a matter of law. In the claims, means-plus-
function clauses are
intended to cover the structures described herein as performing the cited
function and not only
structural equivalents but also equivalent structures.
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