Note: Descriptions are shown in the official language in which they were submitted.
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This invention deals with the installation o~ sanitary sewers and
is particularly concerned with a gasket for sealing the space between a sewer
pipe and an opening in the wall of a manhole through which that pipe passes.
This application is a division of Canadian application No. 292,374 filed
December 5, 1977.
The new form of gasket represents an improvement in the structure
shown in my Canadian Patent No. 996,150, issued August 31, 19760 That
patent shows a gasket made from an extruded rubber strip, having a cross
section in the shape of a capital Ao ~hen properly positioned in the man-
hole opening, the apex of the A is exposed, and extends radially inwardlyto make firm contact with the surface of the pipe 0 The legs of the A extend
outwardly, and are embedded in cementitious material which lines the open-
ing in the manhole wall, as is shown in my Canadian Patent No. 971,997,
issued July 29, 1975. The method of constructing such a seal is described
in my United States Patent no. 3,832,438, dated August 27,1974.
In these earlier patents, in which the elastomeric gasket was
made from an extrusion in the cross-sectional fo~m of a capital A, it
required some distortion of the gasket~ as explained at page 6, lines 16
et seq., of Canadian Patent No. 996,150, to fit this gasket onto the mold
rings, but the webs or skirts (corresponding to the lower legs of the A)
were fairly flexible, so the difficulty of installation proved to be slight.
In spite of the provision of concentric serrations in the web or skirt
portions of the gasket, however, there seemed to be a possibility that,
under severe conditions, the pipe might impose so great a stress on the
gasket as to cause the rubber in the skirt portion under tension to thin out
and pull away from the surface of the concrete in which it was embeddedO
In order to reduce this potential area of vulnerability, experimentation
with other shapes of extrusions was carried outO
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The basic problem was to provide an improved technique for positi-ve-
ly and permanently anchoring the gasket in the cementitious material which
defines the inner surface of the opening. Preferably the gasket has a
double-walled head portion, which has a continuous circular cavity therein.
This cavity is walled with rubber or similar elastomer, and its walls are
air-tight, so that it affords a pneumatic cushion.
The problem did not appear to be solvable by the use of individual
ly molded unitary gasket washers~ since they lacked sufficient resistance to
; compression in their lower~ inner portion, which carries the major load,
and were too subject to peripheral separation from the pipe in their upper
portions. Furthermore, such washers would have to be stocked in many sizesO
Nor did it appear to be feasible or practical to mold a unitary gasket ring
in the form of a washer with a continuous circular cavity, such as could be
made by using the A-shaped extrusionO
The endless cavity of the A-section gasket provided an answer to
the compressibility problem in the pipe-contacting part, but the difficulty
of installation, because the diameter of the inner opening is so much less
than the diameter at the extreme ends of the webs or "legs" of the A, dis-
couraged any attempt to use cross-sectional forms which have to accommodate
an even greater difference between the inner and the outer diameter of the
washer-like gasket, in order to complete installation~
The cross-sectional pattern of the anchoring member of the molded
washer shown in the Netherlands patent to Raatjes, NoO 290,612 of 1963,
seemed to be likely to remain embedded in its surrounding concrete, no
matter how severe the stress upon it might become. But there seemed to be
no way to convert a lineal extrusion having this cross-sectional shape into
a disk-like washer, and no practical way to provide the endless cavity unless
it could be formed by extrusion.
~"washers" as used herein, refers to centrally-apertured articles of disk-
like shapeO
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Combining an extruded triangular head with a T-shaped
anchoring part seemed to be quite out of the question, for this
would greatly increase the overall height of the extrusion, and
thus create an even greater difference between inner and outer
diameter of the finished washer than the A-shaped gasket entailed.
It would apparently be practically impossible to roll the gasket
into place in the molding rings.
It has now been discovered that a seal or gasket having
all of the desired properties can be made by utilizing an extru-
sion having a pipe-contacting part which, instead of being A-shaped,
is pear-shaped in section and is unitarily provided with a T-shaped
anchoring part, the stem of the T being united with the bottom of
the pear-shaped part and affording, when longitudinally considered,
a web of substantial height and thickness. Such an extrusion can
be used effectively if handled in the manner hereinafter set forth.
ccording to one aspect of the invention there is
provided a washer-like gasket of elastomeric material in the form
of a surface of revolution generated by rotating a generatrix
about an axis of revolution, the outline of said generatrix
including a generally pear-shaped head portion integrally joined
to the foo~ of ?~-L~e-~e~-T-shaped flange member in the mid-
region of the bottom of the pear-shaped portion, the axis of
revolution being parallel to the arms of the T member, the pear-
shaped head portion projecting inwardly toward the axis of
revolution and wherein the inner peripheral portion of the washer-
like gasket is in compression and the outer peripheral portion
is in tension.
According to another aspect of the invention there is
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.~ provided Eor use in forming a fluid-tight seal between a pipe and
, a wall opening through which said pipe passes, a washer-like
gasket having inner circumferential portions which are in
compression and outer circumferential portions which are in
tension, said gasket comprising a section of a linear extrusion
of elastomeric material, a cross-section of said extrusion in a
plane normal to the axis of extrusion including a T-shaped flange
and a generally pear-shaped head portion said head portion having
a broad base and tapering along a central axis thereof, said T-
shaped flange having a stem and two arms, said stem bein inte-
at~g~ce~ ;s
grally attached to said broad base of said head portion~, said
D section of extrusion having ends thereof bonded together to form
a ring having an axis offset from and normal to said axis of
extrusion, wherein said central axis of said head portion and
said stem of said T-shaped flange are initially parallel to said
ring axis and said ring is subsequently deflected so that said
central axis of said head portion and said stem of said T-shaped
flange are perpendicular to said ring axis with said head portion
projecting toward said ring axis.
When installing the cut and spliced extrusion in a
manhole opening, the right cylinder is preferably positioned on
the inner portion of a mold, and is rolled inwardly, so that
the pear-shaped pipe-contacting portion is deflected radially
inwardly and the outer flange (corresponding to the cross-bar
of the T in section) and is pulled outwardly, in a manner
analogous to that employed in fitting the bead of a tire to the
metal rim of an automobile wheel. When the inward deflection
of the pipe-contacting part has progressed sufficiently to
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allow it, the complementary part of the mold is slid into place,
and its clamp is drawn up, applying pressure as needed, to force
the tubular part of the ring into the groove which extends
peripherally of the mold.
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~ suitable mold ring for utilizing the novel gasket of this inven-
tion most effectively is the two-part mold which is described and claimed in
Canadian Patent No. 971,9970 ~s there isseen~ mold consists of inner and
outer shells of frustoconical shape which are so configured that when assem-
bled they define between them a peripheral groove which encloses the apex
of the A, leaving the legs of the A free. In the method herein described,
the pear-shaped head of the extrusion is received by the peripheral groove
formed by the mold rings, and the T-shaped flange projects radially out-
wardly therefrom. ~oncrete or other cementitious material is then applied
to enclose the flange and define the peripheral wall of the opening in the
manhole wall. Upon separation and removal of the mold parts, the cementit-
ious material lining the opening covers the peripheral flange and embeds
it, but the tubular pear-shaped portion is exposed, and yields to receive
the pipe inserted therein.
One of the advantages of the present invention is the unexpected
discovery that extrusions having the cross-sectional form described can
; often be used with pipes of different sizes~ without altering their cross-
sectional dimensions. All that is necessary is to change the length of
the extrusion and the diameter of the mold ringsO This capacity to coact
with pipe of many different sizes is believed to be due, in part at least,
to the fact that the manner of use places considerable compression on the
inner portion of the gasket, and causes t~nsion on its periphery~ As a
consequence the gasket described herein hugs the pipe more tightly than
would be the case if the gasket were initially molded as an apertured disk
or washer.
It must be realized that the part of the gasket which lies at the
bottom of the opening when in use will have to sustain mostof the load of
the pipe and its contents, and in addition will have to resist environmental
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stresses, which may be împosed upon the pipe outside of the manhole by the
weight of the fill, or by impacts due to traffic shock, or by the dead weight
of passing vehiclesO If an ordinary washer is used, it may yield too much
under these stresses, and become overly compressed at the bottom of the
opening. The pipe may then pull away from the gasket ~t the upper part of
the opening, thereby allowing fluid to pass the sealO Since the stresses
imposed may sometimes be measured in thousands of poundS,particularly where
the pipe is large - say 24" or 30" in diameter, it is difficult to employ
a molded gasket ring which will manifest both sufficient resistance to
compression at the bottom of the opening and sufficient capacity for expan-
sion at the top.
me pear-shaped head of the gasket described herein is remarkably
adapted to meet this problem. Its walls are of substantial thickness, which
means that a sufficient mass of elastomeric material will be present to
carry the weight imposedO The volume of the preferred circular cavity is
sufficient to afford increased flexibility while the pipe is being installed.
~t the same time, elin~nation of the legs (or webs) of the A of the prior
device avoids formation of a thin edge at the interface with the concrete,
and the rounded edges of the pear-shaped bottom permit a self-accommoda-
ting rolling movement under axial stress.
The other major need is to ensure that the gasket ring is so
firmly anchored in the concrete as to resist any stress which might tend to
dislodge it. This is ensured by the deep embedding of the T-section flange
in the surrounding concrete.
The entire gasket is subjected to substantial distortion as it is
deflected from the cylindrical form which is first produced into an aper-
tured disk or washerO Because the inner diameter of the opening formed by
deflecting the cylinder walls is substantially less than the cut length ofthe
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extrusion, the inner edge of the gasket will be under compression, and con-
versely, because the outer diameter of the washer-shaped finished gasket is
substantially greater than the length of the cut extrusion, it will be under
considerable tension. These twin forces cause the gasket to hug very tightly
the pipe which it surrounds.
Other features and advantages will be apparent from a consideration
of the detailed description which follows, and from reference to the accom~
panying drawings, which illustrate the preferred embodiment of the invention,
and in which:
Figure 1 is an elevation, partly in section, of a manhole structure,
with the gasket seal in position;
Figure 2 is a perspective view of an extrusion used in the method
of the invention,
Figure 3 is a transverse section on the line 3-3 of Figure 2;
Figure 4 is a perspective view, showing the extrusion being pre-
pared for use as a gasket;
Figure 5 is a perspective view of the completed gasket;
Figure 6 is a perspective view showing upper and lower mold forms~
with the gasket ring of Figure 5 in process of installation between them;
Figure 7 is an elevational view , partly in section, showing the
gaslcet of Figure 5 in place in its mold; and
Figure 8 is a vertical sectional view of the completcd installation,
with the sewer pipe in placeO
Turning llOW to Figure 1: The manhole structure 10 is shown with
the sewer pipe 11 passing through it by way of the openings 12,12~ A gasket
13 is shown in the distorted position which it assumes upon insertion of
the pipe 11.
The gasket 13 is formed from a continuous extrusion 14 of rubber
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or the like, illustrated in Figure 2. Preferably, it conforms to ~STM
Specification C 4~3-63T. As seen in the cross-section of Figure 3, the
general configuration of the extrusion is one in which there is a head
portion 15 which is pear-shaped and preferably encloses a symmetrical
hollow or cavity 160 Extending from a mid-part of the outer surface
of the pear-shaped head is a web 17 which interconnects the head 15 with a
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base flange 18 which is normal to the vertical center line~CL of the extru-
D sionO As seen in Figure 2, the form of the extrusion in lengthwise eleva-
tion is that of a tubular head 15 connected by a verticalweb 17 t~ the
longitudinal flange 18 9
The vertical center line CL defines a plane containing the long
axis of the head portion 15 and extending lengthwise with respect to the
extrusion 14~ The base flange or flange structure 18 extends laterally of
the plane and is symmetrical with respect thereto The web means 17 lies
generally in the plane D
It is the apex of the head 15 which makes first contact with a
pipe 11 being inserted in the manhole opening 12. To facili.tate insertion
of the pipe, the apex 20 is rounded, as at 21. Lhlring installation, the base
or anchoring portion~ which consists of the web 17 and the flange 18~ are
.~ 20 embedded in concrete or other cementitious material. The finish line of the
.;~ concrete which will ultimately be present has been suggested by the dashed .
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line 19-19, added to Figure 30 This illustrates the fact that the outer
angles of the pea.r-shaped part are rounded and the concrete is emplaced in
such a way as to avoid a sharp edge of contact with the lower portions of
the pear-shaped tubeO Thus a possibility of accomm~dating some rolling move
ment of the tubular portion of the gasket is provided, to reduce stress on
insertion of the pipe. The cavity 1~ within the tube is preferably sym-
metrical with its outer contour, and is so dimensioned as to provide a fairly
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substantial wall thicknessO The web 17 spaces the base of the head from the
top of the flange sufficiently to afford a substantial channel to be filled
with concrete.
The proportions of the various parts of the extrusion are, in the
preferred embodiment of this invention, substantially as follows. if the wall
thickness be taken as 2x, then 3x is the thickness of the flange 18 and also
the thickness of the web 17; furthermore, the radius of the rounded corners
of the pear shape is also 3x, 4x is the height of the web, and 6x is the
widest dimension of the cavity 16. The total height of the base (web plus
flange thickness) is 7x, which is also the height of the cavity 16. The width
of the base flange is 8x, and the widest part of the pear-shaped head is llxo
The height of the pear-shaped portion is 14x. The exterior surfaces of the
pear-shaped portion diverge at an angle of about 40 (20 on each side of the
vertical) and the base angles are 70 each. The area of the rubber in the
walls of the pear-shaped head is preferably about two and a half times the
area of the cavity.
It is, of course, possible to vary these proportions within limits,
but they have yielded excellent results for most installations. Abnormal
conditions~ such as severe traffic load~ may justify some changes, such as in-
creasing wall thickness without altering other dimensionsO
In order to convert the rectilinear extrusion into a ring gasket,
it is first necessary to cut a piece of it to the desired lengthO Experience
has shown that handling of the completed ring is easier if the length of the
extrusion is 3.26 times the diameter of the pipe to be fitted.
The cut section of the extrusion is then curled into the form of a
right cylinder, and its ends are brought together and vulcanized, as seen in
Figure 4a In order to avoid distortion of the tubular portion of the extru-
sion during vulcanization, it is desirable to insert a dowel pin 23, shaped
to fit the cavity, into the adjacent ends of the tubeO ~he vulcaniz-
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ing clamps are applied when the tube ends have been browght firmly together~
The dowel pin is made of some readily-frangible material, such as plaster
of Paris, and after vulcanization has been completed, it is reduced by
hammering to a fine powder, which does not block the continuous cavity in
the head portion of the gasket.
Figure 5 shows the completed ring, after vulcanization and be~ore
installation in the mold ring to be next described. It will be noted that
the vertical axis of the extrusion is parallel to the cylinder axis, whereas
its intended use requires that the extrusion assume the character of a disk,
extending at right angles to the cylinder axis. In order to effect the
indicated change in form, it is necessary to deflect the walls of the cylin-
; drical gasket into a plane which extends transversely of the axis of the
ring, and then to secure the distorted and deflected base flange by embed-
ding it in concrete or similar cementitious material, with the tubular
pear-shaped portion extending radially inwardly to engage the pipe which
is to be mounted therein.
To accomplish these procedures, it is best to use a mold of the
type described and claimed in Canadian Patent No. 971,997, to which reference
may be had for full detailsO A brief description will suffice for present
purposes~
Figure 6 illustrates the general form of the mold referred to.
It consists of two frustoconical rings 24,25 adapted to be clamped together
and configured to embrace, between them, the tubular, pear-shaped portion
15 of the gasket. Figure 7 is a sectional view of the assembled mold, but
with the parts in inverted position as compared to Figure 60 This clearly
shows how the mold rings provide space between them to receive the tubular,
pear-shaped part of the gasket.
Returning to Figure 6, it will be seen that the gasket ring
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shown in Figure 5 has been stretched to fit the mold ring 25, and is being
deflected radially inwardly, with the tubular pear-shaped part about to be
forced still further down into contact with the mold flange 26 in the
mold ring 25. A truss 27 spans the ring 25 diametrally being welded to a
lug 28 which is long enough to slip through and beyond the aperture 29 in
the corresponding truss 30 which spans the mold ring 24. A quoin key 31 is
used to urge the mold rings together, being inserted into the keyway 32 in
the lug 28 after the rings have been brought togetherO
Figure 7, in addition to showing the gasket ring in its final
position in the assembled mold, also shows the base flange 18 and the web 17
fully embedded in the concrete. The tubular portion of the gasket, being
within the mold, will be free in space after the mold is removed. This
figure illustrates the relationship of the concrete to the pear-shaped
tube, indicated by the dashed lines 19-19 in Figure 30 The concrete should
reach fairly well up on the lower rounded corners of the tube, but not so
far as to permit the formation of a "feather-edge"O Indeed, it is believed
to be desirable to so form the mold as to limit the concrete to a level
approximately the same as the upper surface 16a of the base of the cavity,
so that the gasket may roll a little under the stress imposed by insertion
of the pipe 11.
In Figure 8, the mold rings have been separated and removed and
;; the pipe 11 has been inserted. This causes a fairly extensive distortion
of the tubular part of the gasket, more or less schematically indicated at
13a. The dot-and-dash outline 13 in Figure 8 indicates the position of the
gasket before the pipe 11 is inserted.
The sloping conical faces 33,3~ are provided for the purpose of
accommodating misalignment of the pipe 11, The curvature of the dash lines
35,36 indicates the projected circumference of the manhole wall which lies
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above and below the locus of the opening 120
For convenience it may be desirable to conduct much of the work
involved in the shop rather than in the field. If this is desired, the mold
may be assembled within an outer form, so that the concrete in which the
flange is embedded is in the shape of a tubular concrete plug, preferably
cylindrical, of a size to fit the opening in the manhole wall. It is then
carried to the site, and cemented into place within the opening.
In any event, after the gasket is in place and the concrete is
sufficiently cured, the pipe 11 is inserted through the gasket 13, causing
substantial distortion of the tubular portion, as suggested at 13a. This
greatly extends the contact area, so that there is very little chance that
minor pits or defects in the pipe will escape the sealing action.
The wall thickness of the head and the si~e of the ca~ity within
; it are so related as to ensure the presence of enough rubber or rubber-like
material to sustain the weight imposed and yet cushion the load to protect
against shocks and momentary stressesO At the same time, the tension imposed
on the circumference of the gasket ensures that tight contact will be main-
tained at the upper surface of the pipe, no matter how extensi~ely the tub-
ular head may be compressed at its lower portion.
This combination of factors, including the expanded area of contact
and the cushioning action, protect against minor defects in the pipe surfaceO
Should there be a situation in which the pipe at the locus of the gasket is
seriously out of round, or locally flattened, it may be desirable to increase
the tightness of the seal by injecting a non-hardening, self-sealing material
into the circular cavity, using a syringe with a fine point for this pur-
pose. The material injected is placed under sufficient pressure to expand
the tubular head into close contact with the pipeO The pressure needed may
be supplied mechanically by the syringe, or chemically, as by
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using urethane and a foaming agent, in controlled proportions, When the
syringe is withdrawn, the self-sealing material inserted closes the opening
made by the point of the syringeO Needless to say, this expansion-producing
material is not employed until the pipe is in place.
It is noted that the contours of the A-shaped gasket previously
used are significantly less well adapted to the need than is the new con-
tour. The inverted "T" which forms the base element of the extrusion is so
firmly embedded in concrete as to be practically incapable of removal , since
the thrust imposed by insertion of the pipe is substantially normal to the
web 17, and is transmitted through a very substantial body of rubber-like
material, whereas the thrust, when using the A-shaped washer, is almost
parallel to the leg of the A which is first contacted by the entering pipe,
thus incurring the likelihood that the leg (or skirt portion) will be
stretched and thinned out, and possibly torn out by the roots, so to speak.
The rounding of the lower corners of the pear-shaped contour, in contrast,
permits the gasket to roll a little to accommodate stress, while the
embedding of the T-shaped anchoring part of the gasket positively prevents
dislodgement. The avoidance of any feather-edge at the interface between
gasket and concrete eliminates any tendency o~ the concrete to break away
or chip out in that location.
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