High pressuure coupling for plastic pipe and conduit

A length of corrugated tubing is (B) inserted into a bell (C) having an open end 42. The corrugated tubing is defined by alternating annular portions peak (22) and valley portions (24) and a cylindrical inner wall (26) connected with an inner surface of the valley portions. Annular chambers (28) are defined between the cylindrical inner liner and each peak portion. The bell has a stop (10) and a cylindrical side wall (40) with a groove (44) for receiving a gasket (30) that is disposed in one of the tubing valleys. The groove is constructed an integer number of peak and valley portions from the stop such that the gasket aligns with the groove when an end of the tubing length abuts the stop. A plurality of latch elements (60) are disposed an integer number of peak and valley portions from the gasket receiving groove toward the bell open end. The latch elements extend into another of the valley portions and engage a corrugation side wall to transfer axial uncoupling forced from the tubing to the bell side wall. Each latch element is hingedly connected (70) with the bell cylindrical side wall. The latch elements each include a cam surface (64) which engage peak portions of the received tubing length and are cammed radially outward such that the latch elements pivot radially outward to facilitate receipt of the first length of corrugated tubing.

BACKGROUND OF THE INVENTION 
The present invention relates to the art of connecting tubing, pipes, and 
conduit. It finds particular application in conjunction with the 
interconnection of large diameter, smooth interior wall corrugated plastic 
tubing and will be described with particular reference thereto. However, 
it is to be appreciated, that the invention will also find application in 
conjunction with smooth-walled, corrugated, and other types of pipe and 
tubing. 
Large diameter plastic pipe, e.g. 24 inch (60 cm) plastic pipe, is commonly 
shipped and handled in sections, e.g. 20 foot (6.5 m) sections. Each 
length has a stiff, self-supporting outer wall which includes alternating 
peaks and valleys that define a series of corrugations. Optionally, a 
lighter-weight continuous tubular liner extends along and is connected 
with the valleys to define a smooth interior diameter. Tubing with a 
smooth interior diameter has a substantially higher fluid carrying 
capacity than tubing with a corrugated interior of the same diameter. 
To connect the lengths of tubing, external bell couplers are often 
utilized. The external bell couplers include a plastic sleeve or bell 
connected to one end of a tubing length. The bell has an inner diameter 
which substantially matches the outer diameter of the corrugation peaks of 
the tubing length to be connected. Typically, a stop is defined to provide 
an abutment for the end of the connected tubing length. 
Internal couplers are also used to connect lengths of tubing. Internal 
couplers include a plastic sleeve whose outer diameter substantially 
matches the inner diameter of the corrugation valleys of the tubing 
lengths to be connected. One or more outwardly projecting corrugations are 
defined in the center of the coupler to mark the center and to provide an 
abutment for the ends of the connected tubing lengths. Internal couplers 
are generally used to connect corrugated tubing without internal tubular 
linings. The internal coupler with cleats could not be readily used in 
connection with internal tubular liners because the internal tubular liner 
interferes with the outward projecting cleats. The coupler cleats could 
not extend into the internal valleys due to the tubular liner. 
To provide a fluid tight seal, an annular gasket can be disposed in one of 
the corrugation valleys which will be received within the coupler. 
Generally, the tighter the gasket presses against the cylindrical interior 
surface of the coupler, the more pressure the joint can be expected to 
hold. As the end of the tubing length is inserted into the coupler (or the 
coupler inserted around the end of the tubing length), the gasket is 
compressed into the valley and firmly against the interior cylindrical 
surface of the bell. 
In the past, attempts to improve the seal and raise the failure pressure 
have focused on the gasket. In particular, the gaskets are now compressed 
sufficiently that water does not flow between the gasket and bell. To 
facilitate insertion with this high compression of the gasket, the 
interior surface of the coupler bell is commonly coated with a lubricant. 
This facilitates pressing the coupling and the end of the pipe together, 
typically with axial pressure from a backhoe. Although the gasket/bell 
interface withstands well over 10 psi, the couplings still fail at about 
10 psi. 
The inventors herein have discovered an unexpected failure mode. With 
reference to FIGS. 1A and 1B, the internal pressure in the pipe feeds back 
around the end of the pipe to the gasket. The gasket acts like a piston in 
the coupler sleeve. The pressure tries to push the piston or gasket out of 
the coupler sleeve in a direction which tries to compress the pipe 
axially. This first axial compressire force is combined with a second 
force which also urges the pipe to compress axially. The annular chambers 
defined between the smooth inner liner and the corrugation peaks typically 
have a very small weep hole to allow the pressure within these annular 
regions to equalize with the external environment. As the pressure in the 
interior of the pipe increases, there is an increasing pressure 
differential between the interior of the pipe and the annular regions 
below the corrugation peaks. This pressure differential causes the inner 
liner to arc into the annular regions and the corrugation peaks in the 
coupler bell to draw together axially or fold in an accordion-type style. 
Backfill around corrugations outside the coupler tends to fill the 
corrugation valleys and resist this accordion-type contraction. However, 
the corrugations adjacent the gasket are shielded from the backfill by the 
bell. The corrugations on the high pressure side of the gasket are not 
subject to the first axial compressire force and are only subject to the 
second compressive force until the pressure equalizes through the weep 
hole. The corrugations on the low pressure side of the gasket are subject 
to both pressures. 
As these two axial pressures cause the corrugations to contract in an 
accordion-like manner, the length of tubing section becomes shorter. 
Because the central region of the tubing section is well anchored by the 
backfill, the gasket and the end of the tubing move toward the central 
portion of the tubing section and are withdrawn from the coupler. In a 
double bell connector, the end of the tubing connected to the other bell 
withdraws analogously, but in the opposite direction. This axial 
compression or shortening of the pipe continues until the gasket is pulled 
from the bell or until the pipe compresses further on one side than the 
other. Such uneven compression or crushing of the pipe causes a rotation 
of the gasket out of the vertical plane (when the longitudinal axis of the 
pipe is horizontal) which also pulls the gasket away from the bell. The 
lubrication which was used to allow the gasket to seal more completely to 
the interior surface of the bell actually facilitates the movement of the 
gasket and failure of the joint. In this manner, the solution dictated by 
the conventional wisdom discussed above, i.e., compressing the gasket so 
hard that a lubricant is required for its insertion, is actually promoting 
the failure. 
The present invention contemplates a new and improved coupling arrangement 
which overcomes the above-referenced problems and others. 
SUMMARY OF THE INVENTION 
According to one aspect of the present application, a tubing coupling 
system is provided. The tubing coupling system includes a length of 
corrugated tubing having a corrugated side wall defined by alternating, 
annular peak and valley portions and a cylindrical inner wall connected 
with an inner surface of the valley portions. Annular chambers are defined 
between the inner liner at each peak portion. A bell is provided having an 
open end into which the corrugated tubing length is received and a 
generally cylindrical side wall. The cylindrical side wall has a 
cylindrical interior surface in which a gasket receiving groove is 
defined. Latch elements are configured circumferentially around the bell 
side wall extending radially inward. Each latch element extends into one 
of the valley portions of the received corrugated tubing length and 
engages a corrugation side wall to restrain axial movement between the 
bell and the length of corrugated tubing. 
According to another aspect of the present application, each latch element 
is hingedly connected with the cylindrical wall such that the latch 
elements pivot radially outward to facilitate receipt of the first length 
of corrugated tubing. 
In accordance with another aspect of the present invention, the bell 
defines a stop to limit receipt of the corrugated tubing length. The 
gasket receiving groove is defined on integer number of corrugation peak 
and valley portions from the stop such that a gasket received in one of 
the corrugation valleys is received in the groove. The latch elements are 
disposed on integer number of peak and valley portions from the groove 
toward the bell open end such that the latch elements are received in 
another corrugation valley of the tubing length. 
One advantage of the present application is that it insures a more reliable 
coupling between corrugated tubing lengths having a smooth inner tubular 
liner. 
Another advantage of the present application relates to the ease at which 
the corrugated tubing is inserted into the coupling bell. 
Another advantage of the present invention is that it permits water tight 
and non-water tight connections with the same coupling bell. 
Still further advantages of the present invention will become apparent to 
those of ordinary skill in the art upon a reading and understanding of the 
following detailed description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 2, a double bell coupler A receives ends of a first 
and second lengths of corrugated tubing B in opposite facing coupling 
bells C. The double bell coupler A defines an inward valley or stop 10 
annularly around its geometric center. The stop 10 serves to limit the 
extent of engagement of the tubing ends to assure that each is received to 
the same, proper depth. 
With continuing reference to FIG. 2 and further reference to FIG. 3, each 
length of corrugated tubing B includes a stiff, strong corrugated outer 
wall 20 made up of alternating ridge or peak portions 22 and recess or 
valley portions 24. The corrugated outer wall has sufficient strength to 
withstand flattening compression from surrounding earth. To provide for 
higher fluid carrying capacity, a cylindrical inner liner 26 extends along 
an inner diameter of the corrugation valleys and is integrally connected 
thereto. The cylindrical liner or wall 26 is lighter weight than the 
corrugated outer wall but still carries a significant part of the axial 
load. The inner liner 26 and each of peaks 22 define an annular region 28. 
Each peak contains a weep hole which allows pressure in the annular 
regions 28 to come into equilibrium with the external pressure. 
For a fluid-tight seal, a gasket 30 is received in one of the corrugation 
valleys 24 of each corrugated tubing length. The gasket is constructed of 
a rubber which is readily deformed by pressure. The gasket includes an 
angled, outward projecting flange or flap 32 which is compressed as the 
tubing is inserted into the coupler bell C. 
Each coupler bell C includes a cylindrical sleeve or wall portion 40 that 
has an inner diameter which is the same as or slightly larger than the 
outer diameter of the corrugation peaks 22. The cylindrical sleeve portion 
40 has a flared outer end 42 to facilitate receipt of the end of the 
tubing length and compression of the gasket 30. A force transfer means is 
provided for transferring an axial uncoupling force on the tubing to the 
bell such that the axial strength of the bell strengthens the joint. First 
the axial force transfer means includes an annular groove 44 defined in an 
inner surface of the cylindrical side wall substantially in alignment with 
the gasket 30. Most commonly, the tubing sections are cut generally 
centrally in one of the valleys 24. The gasket is placed a preselected 
number of corrugations from the end, preferably in the first valley. The 
gasket flange 32 has a generally flat end wall 46 and the groove has a 
mating generally flat end wall 48. The relative angle of the end wall 48 
is selected such that the gasket end wall 46 abuts it squarely. The axial 
force is transmitted from the tubing corrugations, through the gasket and 
gasket flange to the groove flat end wall and the bell cylindrical wall 
portion. 
In the embodiment of FIG. 3, the groove further defines a forward wall 50 
which is positioned to limit outward movement of the flange member 32. The 
groove is defined one corrugation from the stop 10 such that the gasket 
flange 32 is received therein. As the end of a length of tubing and a 
coupler are pushed together, generally with a backhoe, the flared end of 
the coupler A compresses the gasket into valley 24. Continued axial 
pressure slides the tubing end and the coupler together until the gasket 
reaches the groove. The gasket expands rapidly or snaps into the groove 
producing an audible indication that the insertion is complete. 
The axial force transfer means further includes a set of cleats or latching 
elements 60 integrally formed with the coupler bell C and which extend 
generally, radially inward of the bell cylindrical wall portion 40. The 
latching elements are spaced around the circumference of the cylindrical 
wall portion and positioned between the annular groove 44 and the flared 
end 42. Preferably, four latching elements spaced 90.degree. apart are 
utilized although a greater or lesser number could also be employed. The 
equal spacing between the latching elements provides equal retaining 
forces circumferentially around the coupling bell. 
With particular reference to FIGS. 2 and 3, each latching element includes 
a corrugation engaging wall 62 and a cam surface or tapered wall 64. The 
engaging wall is disposed generally normal to the cylindrical wall portion 
40. The latching elements are spaced an integer number of corrugations 
from the annular groove 44 such that the engaging wall squarely engages an 
outer surface 66 of one of the corrugation side walls. The camming wall 
faces generally towards the bell flared end 42 to engage and be cammed 
outward by the peak portions 22 as the tubing and coupler are pushed 
together. Preferably, in operative engagement, the latching elements 
extend into the second valley from the corrugated tubing end, and act to 
limit axial movement between the tubing and coupling bell as will be more 
fully described below. 
The plastic of the bell cylindrical wall portion defines a hinge area 70 at 
the base of the latch element cam surface 64 to allow the latching element 
to rotate or pivot resiliently outward as the latching elements slide over 
the peak portions 22 during insertion of the tubing into the coupling 
bell. A tab or flap 72 is integrally connected to the engaging wall of 
each latching element extending generally towards the bell stop 10. The 
tabs or flaps are preferably defined by a semi-circularly shaped cut-out 
74 extending from the hinge area around the cleat and back to the hinge 
area. The configuration of the cut-out 74 may depart from the illustrated 
semi-circular shape without departing from the inventive aspects of the 
subject development. For example, rather than a cut-out 74, a thin walled 
bellow, frangible perforations or the like can be provided to allow 
outward rotational movement of the latch element. The tab or flap extends 
from the engaging wall and abuts an adjoining corrugation peak. Under an 
axial uncoupling force on the tubing, the engagement between the tab 72 
and the corrugation peak 22 prevents the cleat from pivoting fully into 
the valley and cushing. 
In the embodiment of FIG. 4, the bell C is welded or otherwise permanently 
affixed to one end of a length of corrugated tubing B or other associated 
structure. An end of the corrugated tubing B defines the stop surface. The 
gasket receiving groove 44 and the latch elements 60 are again spaced 
integer numbers of corrugations from each other and the stop surface. 
It will be noted that a secure interconnection is achieved even to tubing 
B' without the gasket 30. Where an assurity of a fluid tight seal is not 
needed, the gasket need not be used. 
During installation, the first end of the corrugated tubing is inserted 
into the flared end 42 of the coupling bell C. As the tubing continues to 
be inserted, the flaps 72 rotate about the hinge region 70 allowing the 
latching elements 60 to be cammed over peak portions 22 of the corrugated 
tubing. When the latch elements clear a peak portion, they snap into 
locking engagement behind it. In this position, the engaging surface 62 
squarely engages oppositely facing outer surface of the side wall 66. 
An axial tension pulling force applied to either the corrugated tubing 
length or the coupling bell would urge the joint to uncouple or detach. As 
described above, the axial force is created by internal tube pressure. 
When the pressure in the tubing increases, there is an increased pressure 
differential between the tubing interior and the annular regions 28. As 
the pressure continues to increase, there is a tendency for the inner 
liner 26 to buckle into the regions 28 and for the side walls of the 
corrugation to move together. Backfill tends to fill the corrugation 
valleys of the central portion of the tubing lengths away from the coupler 
providing increased resistance to axial compression. Axial compression of 
the tubing tends to cause the end of one (or both) of the tubing lengths 
to pull out of the coupler. The insufficient strength relative to axial 
compression permits the side walls of the corrugations to move together, 
compressing the corrugations axially and allowing the tubing to contract 
or shorten in length. 
With the present coupler, the axial tension force is transferred through 
the gasket 30 and the latch element 60 to the coupler. In this manner, the 
axial extension strength of the coupler is added to the axial compression 
strength of the corrugated tubing. 
The invention has been described with reference to the preferred 
embodiments. Obviously, modifications and alterations will occur to others 
upon reading and understanding the preceding detailed description. It is 
intended that the invention be construed as including all such 
modifications and alterations insofar as they come within the scope of the 
appended claims or the equivalents thereof.