Pipe coupling with interlocked and segmented grip ring

A pipe coupling for connecting a pipe (6) to a fitting (5). The coupling comprises an annular assembly (1) incorporating a gripping ring (4) for inserting into a radial gap between the pipe (6) and the fitting (5), and structure (8,9) for applying an axial load to the annular assembly (1) so that the gripping ring (4) is biased radially against the pipe (6). The gripping ring (4) is defined by a plurality of separable segments dimensional such that when the annular assembly (1) is axially compressed each of the segments is biased against the pipe (6).

FIELD OF INVENTION 
The present invention relates to a pipe coupling for connecting a pipe to a 
fitting. 
DESCRIPTION OF THE PRIOR ART 
Many different pipe couplings have been proposed in the past for connecting 
pipes to fittings. The pipes are generally circular in cross-section and 
the fittings may be of a variety of forms, for example fittings to 
interconnect two pipes end to end, fittings to connect a pipe to devices 
such as valve housings, and fitting to form elbows, T-junctions or the 
like. The present invention is applicable to any situations in which one 
end of a pipe has to be connected to any other component. 
It is highly desirable to be able to make secure connections to plain ended 
pipes, that is pipes the ends of which do not support formations such as 
flanges against which the coupling can bear to provide pull-out 
resistance. Such pipes are often used to convey potentially hazardous 
fluids such as flammable pressurised gases or liquids. If the couplings at 
each end of the pipe do not positively grip the pipe ends there is risk 
that the pipe ends will be pulled from the fittings. 
Couplings have been devised which incorporate a sealing ring that not only 
provides a good fluid-type seal between the fitting and the pipe but also 
grip the pipe end to provide enhanced pull-out resistance. One example of 
such a sealing ring is described in British Patent Specification GB 
2167145. In this patent specification a sealing ring is described which is 
fabricated from a resilient material in which gripping members are 
embedded. When the coupling is assembled the sealing ring is compressed in 
such a manner that the gripping members are biased radially inwards 
against the outer wall of the pipe. As the coupling is tightened up the 
gripping members bite into the pipe wall and provide good pull-out 
resistance. The manufacture of such sealing rings incorporating embedded 
gripping members is however a relatively complex procedure and as a result 
the couplings are relatively expensive. This is of particular importance 
where a full range of couplings must be provided to enable the user to 
select from the range couplings appropriate to a variety of different pipe 
diameters. Economies of scale are therefore difficult to achieve. 
It is an object of the present invention to provide a pipe coupling which 
obviates or mitigates the problems outlined above. 
SUMMARY OF INVENTION 
According to the present invention there is provided a pipe coupling for 
connecting a pipe to a fitting, the coupling comprising an annular 
assembly incorporating a gripping ring for insertion into a radial gap 
between the pipe and the fitting, and means for applying an axial load to 
the annular assembly so that the gripping ring is biased radially against 
the pipe, wherein the gripping ring is defined by a plurality of separable 
segments, characterized in that adjacent segments of the gripping ring are 
directly interlocked, and at least a plurality of the segments are 
gripping segments which are dimensioned such that when the annular 
assembly is axially compressed the gripping segments are biased against 
the pipes. 
To achieve interlocking, adjacent segments in the gripping ring may be 
interlocked by loose dovetail interengaging formations. Each segment may 
be a gripping segment, or alternatively a plurality of spacer segments may 
be provided, adjacent gripping segments in the gripping ring being 
interconnected by spacer segments with which the gripping segments are 
interlocked. 
Preferably, the annular assembly comprises a resilient sealing ring. A 
force transmitting ring is preferably interposed between the gripping ring 
and the sealing ring. The force transmitting ring and the sealing ring 
could be incorporated together so that only one component part would be 
required in the annular assembly to perform both sealing and force 
transmission functions. 
The fitting may define a housing into which one end of the pipe is 
inserted, the annular assembly extending around the pipe inside the 
housing. In such an arrangement, the fitting may comprise an annular 
housing having a first end which is in sliding engagement with the socket 
and a second end defining a shoulder extending radially inwards and facing 
towards the first end, the sealing ring being received within the first 
end of the housing, the gripping ring being located between the sealing 
ring and the shoulder, and the axial load applying means comprising means 
for forcing the shoulder of the annular housing towards the socket so as 
to compress the annular assembly between the socket and the said shoulder. 
Alternatively, the fitting may comprise a tubular body one end of which is 
inserted in the end of the pipe, the annular assembly extending around the 
tubular body inside the pipe. The tubular body may have a radially 
outwardly extending shoulder adjacent its said end, and the axial load 
applying means may comprise means connected to the tubular body for 
pushing the annular assembly against the said shoulder.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to the accompanying drawings, the coupling comprises an annular 
housing 1 in which is received an annular assembly incorporating a 
resilient sealing ring 2, a metal ring 3, and a gripping ring made up from 
a plurality of individual segments 4. The annular housing 1 engages a 
tubular socket 5, the housing 1 and socket 5 defining a fitting to which a 
pipe 6 is to be connected. The fitting of which the socket 5 forms a part 
may be of any type and could be for example a straight connector for 
interconnecting two pipes end to end, in which case the components 
illustrated in FIG. 1 are duplicated at either end of the socket 5. In the 
illustrated case the pipe 6 is of polyethylene and accordingly a metal 
insert 7 is provided in the pipe end to prevent the pipe end from 
collapsing radially inwards. Tension bolts 8 extend through the annular 
housing 1 such that when nuts 9 are tightened the annular assembly is 
pulled against the socket 5. The end of the annular housing 1 adjacent the 
socket 5 is a loose sliding fit over the socket 5. 
FIG. 2 is an exploded view of the components shown in FIG. 1 and FIG. 3 is 
a section through FIG. 1 on the line III--III. FIG. 4 illustrates two of 
the gripping segments 4 and it can be seen that each of the gripping 
segments is identical and incorporates a tongue 10 with an enlarged end 
and a keyhole-section socket 11 into which the tongue 10 of an adjacent 
segment can be lipped in the axial direction. This is one example of a 
"dovetail" type interengagement between segments. Thus each of the 
segments can move relative to its two neighbours in both the axial and 
circumferential directions. It can also be seen from FIGS. 1 and 4 that 
the side of each segment facing the pipe 6 is provided with serrations 12. 
Referring to FIGS. 5 and 6, the sealing ring 2 in its free state defines a 
peripheral lip 13 extending radially outwards from a main body 14 which is 
of generally triangular cross-section. A groove 15 reduces the pressure 
required to cause some axial displacement between the lip 13 and the body 
14. An inclined surface 16 is in use positioned adjacent the ring 3. An 
inner lip 17 has a diameter less than that of the minimum expected 
diameter of the pipe 7 onto which the assembly is to be fitted. 
When the coupling is to be assembled, the assembly comprising the housing 
1, the sealing ring 2, the ring 3 and the gripping segments 4 is simply 
slipped over the pipe end. As the segments 4 are only loosely retained 
within the housing they easily ride up over the end of the pipe and are 
prevented from being pushed out of the assembly by the engagement between 
the sealing ring lip 13 and the mating groove 18 in the housing 1. The 
sealing ring is initially distorted as a result of the internal diameter 
of the sealing ring being less than that of the pipe. The pipe end is then 
inserted into the socket 5, the bolts 8 are inserted and the nuts 9 are 
tightened up. This pulls the annular assembly onto the socket 5. An axial 
compression force is applied by the shoulder 19 to the segments 4 and this 
axial compression force is transmitted through the ring 34 to the sealing 
ring 2. The sealing ring 3 is compressed against the socket 5 and as a 
result the sealing ring 3 fills the space between the socket 4, the pipe 6 
and the housing 1. Thus a good fluid tight seal is defined between the 
socket 5 and the pipe. The axial compression force also causes a radial 
compression force to be applied to the segments 4 as a result of the 
tapering surfaces of the ring 3 and the shoulder 19 and the tapering 
adjacent surfaces of the segments 4. The serrations 12 of the segments are 
thus forced radially inwards to engage the pipe 6. If tension is 
subsequently applied to the pipe 6 it is prevented from pulling out of the 
socket 5 by this engagement between the segments 4 and the pipe. 
As the gripping ring is in the form of a series of segments 4 and can 
easily be pulled over even a distorted pipe of oval cross-section. The 
resistance to forces tending to pull the pipe away from the fitting is 
very large, typically grater than that required to result in failure of a 
polyethylene pipe for example. 
FIG. 7 illustrates an alternative embodiment of the invention suitable for 
forming a seal with the inner wall of a pipe. In FIG. 7, a pipe 20 
receives a tubular fitting body 21 around which are positioned a sealing 
ring 22, a force transmitting ring 23, segments 24 (which may be identical 
to those illustrated in FIG. 4), a tubular push ring 25, and a nut 26 
engaging a thread 27 provided on the body 21. The nut 26 can be tightened 
to apply an axial load to the ring assembly, thereby compressing the 
sealing ring against a shoulder 28 supported in the body 21. The axial 
load also forces the segments 24 radially outwards to grip the pipe 20. 
A significant advantage of the described arrangements is that gripping 
rings of different nominal diameter can be produced simply by adjusting 
the number of segments in each gripping ring. Thus a single basic 
component can be used to form gripping rings suitable for a wide range of 
nominal pipe diameters. It is of course necessary to provide sealing rings 
and force transmitting rings matched to the particular pipe size but as 
these components are fabricated from a single material this can be done 
relatively cheaply. 
Although in the described embodiments the gripping segments are 
interengaged by dovetails it will be appreciated that alternative means 
for retaining the gripping elements in position could be provided. 
The coupling in accordance with the present invention can be fabricated 
from any suitable material. For example the gripping segments may be 
moulded from a hard plastics material such as acetal or fabricated from 
any appropriate metal. The sealing ring can be fabricated from any 
suitable elastomeric material. The invention can be used with plastics 
piping such as polyethylene or any other type of piping such as steel or 
other metal materials. The force transmitting ring interposed between the 
sealing and gripping rings may be manufactured from metal or a hard 
plastics material and may be supplied adhered to the sealing ring. Any 
appropriate mechanism may be provided for compressing the annular 
assembly, for example arrangements such as those shown in the accompanying 
drawings or any other arrangement capable of providing axial and radial 
compression. 
It is important to note that the described arrangements can form effective 
joints even with distorted pipes of non-circular cross-section. 
Furthermore, efficient joints can be formed even between components which 
are axially inclined to each other. The couplings are also capable of 
resisting pressure fluctuations in which the internal pipe pressure is 
greater than or less than the external pressure. Furthermore more than one 
sealing ring and more than one gripping ring can be provided if this is 
required to meet operating conditions. The couplings are applicable in 
systems carrying gases, liquids, solids or combinations thereof, and can 
be supplied to the end user with the ring components ready assembled.