Note: Descriptions are shown in the official language in which they were submitted.
~31L~98~
Pipeline systems generally consist of individual pipes
of different lengths, and also of different diameters, which
are joined together at their ends with pipe couplings. Located
at various points along the systems are fittings of various
kinds, for example cocks, valves or shut-off gates which are
connected to adjoining pipes in the same way. All of these
joints must be as strong and leakproof as the individual
lengths of pipe. This applies to both metal pipes and plastic
pipes. The latter may be made entirely of plastic, to wit a
thermoplastic synthetic material, but they must also be made
of a composite material, with reinforcements and reinforcing
elements, more particularly in the form of glass fibres
embedded in a duroplastic material. These are known as GFR
pipes. Since they are, in any case, made in layers, it is
possible to make different layers out of different plastics
which are particularly well suited to particular purposes.
In the case of high-strength metal pipes, it is normal
to use coupling elements made oE metal, so-called "fittings",
the ends of the pipes and the coupling parts being provided
with cut threads so that they can be screwed directly together.
There are also cutting ring joints i.n which the end cutting
edge of a cutting ring is forced into an internal cone, so that
the end cutting edge contracts and cuts into the pipe
surrounding it. This kind of pipe joint may also be used for
low-strength metal pipes but not for plastic pipes.
~k
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For plastic pipes there are permanent joints in which
pip2 sections are joined together by welding or gluing, or by
means of coupling elements. When the ends of two pipes are
welded together, an internal burr is often produced at the
weld. This may substantially restrict the internal diame-ter
of the pipe and cause turbulence in a fluid passing
therethrough. Glued joints require considerable care in their
execution which must be carried out by skilled tradesman. Even
then, glued joints cannot always be produced on site with
lo sufficient reliability. Moreover, glued joints may be attacked
by certain fluids and/or by the content of the fluid and, for
this reason alone, they cannot always be used. One great
disadvantage is that susceptibility to a fluid, or to the
content thereof, may be discovered, ovex the course of time,
after the joint has been made, in which case the whole system
may have to be replaced. Another major disadvantage of both
welded and glued joints is that the joints can never be
disconnected again when changes are needed in the system and
when additional connections are required.
For pipeline systems using plastic pipes there are also
detachable joints in the form of clamped connections of
different designs. Common to all of these is a clamping part
which can be deformed, a clamping ring, between which two
conical locating surfaces, adapted to move in relation to each
other, are clamped axially. As a result of the resilient
change in shape produced, the clamping ring bears tightly, on
the one hand against the pipe and, on the other had, against
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another part of the pipe coupling, thus uniting khe two ends
of the pipe firmly together.
In many of the clamped pipe connections, a supporting
sleeve is frequently required. This may either be a loose part
which is inserted into the end of the pipe, or it may be
moulded to the ccupling element, being pushed into the pipe
with the coupling part when the pipe is joined.
These supporting sleeves, which are of many kinds, have
the major disadvantage of bringing about a considerable cross
sectional constriction in the pipeline. This always results
in a corresponding pressure drop and is often associated with
a considerable amount of noise. In the case of pipeline
systems comprising a large number of fittings, pressure drops
at successive joints may add up to a very high value. The use
of supporting sleeves also has another major disadvantage,
namely that the end of the pipe must be heated before the
supporting sleeve is pushed into it or before the pipe is
pushed into the coupling element with the moulded-on sleeve.
Unskilled heating may damage the pipe. There are also clamped
pipe connections without supporting sleeves, in which the
clamping rings are always slotted continuously at a peripheral
location because, in the absence of the supporting sleeve,
resilient deformation of the pipe is relatively major,
especially in the vicinity of the conical surfaces between the
supporting ring and the coupling screw. ~n additlon to this,
and especially in the case of pipes made of a thermoplastic
synthetic material, it is known that dimensional tolerances are
very larqe and a large change in diameter and/or diametrical
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tolerance, must be bridged. This longitudinal slotting makes
it impossible for the clamping rings to ensure a seal, making
it necessary to use an O-ring as the actual sealing element.
A recess is provided in the coupling element.
In one type of clamped pipe connection, the O-ring is
inserted into a groove having two shoulders on the inside of
the coupling element. It is pressed by the fluid itself
against the shoulder lying outside in the direction of
pressure, and this provides the sealing action. In ano-ther
type of clamped connection, the 0-ring is inserted into an
axial recess in the coupling element, where it bears against
one side of the O-ring and this is pressed against the 0-ring
by the pipe joint coupling screw. It is thus deformed
resiliently in the remaining cavity and bears tightly, in the
radial direction, on the one hand against the coupling element
and, on the other hand, against the outside of the pipe.
In the first of these clamped pipe connections, the pipe
is held by a clamping ring which is seated upon the pipe
externally of the O-ring and is pressed against the coupling
element by a coupling nut. The latter comprises an internal
conical surface which co-operates with an external conical
surface on the clamping ring and, when the coupling nut is
tightened, ensures that the sharp inner edges of the peripheral
annular ribs, located on the inside of the clamping ring, cut
into the outside of the pipe. In the second of these clamped
pipe connections, the clamping ring is located between the
thrust-ring for the O-ring and the internal conical surfaces,
remote therefrom, of a coupling screw. This clamping ring,
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when the coupling screw is tightened, is also dePormed
radially, inwardly and resiliently so that, here again, the
internal annular ribs cut into the outside of the pipe. At the
same time, the head of the coupling screw presses the thrust-
ring against the O-ring.
In these two types of clamped pipe connection, the 0-
ring ensures sealing at the joint, whereas the annular ribs on
the inside of the clamping ring provide the necessary holding
force between the pipe and the coupling. This force cannot be
provided by the O-ring alone but is necessary to prevent the
pipe system from being pulled apart by the pressure of the
fluid. These clamped pipe connections having O-rings have the
disadvantage that the O-rings do not have a very long life and
that they undergo changes in the course of time when used with
fluids at varying pressures and, especially, at varying
temperatures, as a result of which the sealing action declines
or disappears completely. In this connection, the increasing
creep in the material of the O-rings is a disadvantage.
These clamped pipe connections also have the
disadvantage that the clamping ring is clamped between the pipe
and an internal ronical surface of the coupliny nut or coupling
screw, so that as these are tightened, considered torque is
applied to the pipe through the adjacent conical surfaces. If
fittings are already connected to the pipeline, twisting of the
pipe must be prevented. If the pipe is held by existing
fittings, the clamped connections thereof may be loosened
again. If the pipe itself is held, it may be damaged since
this re~uires the use of grips.
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In these clamped pipe connections, the clamping force
of the clamping ring is produced by co-operation between the
conical surfaces and the clamping ring, on the one hand, and
the coupling nut or screw on the other hand. Since the flank-
angle is relatively steep in relation to the longitudinal axis
of the pipe coupling, the conical surfaces have only a very
short axial extension and the radial force applied to the pipe
by the clamping ring is concentrated in a very short
longitudinal section of the pipe. This means that the pipe is
subjected to very high local stresses, leading to relatively
sharp resilient constriction at this location. There is also
the danger of the annular ribs on the cutting ring cutting very
deeply into the outside of the pipe over this short
longitudinal section. This causes a considerable notch-effect
in the pipe, concentrated over a very short length, leading to
a very considerable reduction in the fatigue strength of the
pipe.
It is the purpose of the invention to provide a clamped
pipe connection which has greater fatigue strength than
existing clamped connections.
When the coupling screw or coupling nut, as the
actuating member of the clamped connection, is tightened, the
clamping ring is first of all pressed axially into the very
slender internal cone of the coupling element which is thus
constricted resiliently. As the resistance to displacement in
the unslotted longitudinal section at the front end of the
clamping ring increases, so does the axial locating force at
the rear end of the clamping ring, and the also flat locating
MLS:HWR 6
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surface on the actuating member increases. This increases the
frictional force between these two surfaces in the peripheral
direction. The spiral slot then causes the adjacent turns of
the clamping riny to constrict, so that its external conical
surface bears less heavily against the internal conical surface
of the coupling element, while the cylindrical inner side bears
increasingly heavily upon the pipe. In this way, the unslotted
longitudinal section at the front end of the clamping ring is
pushed over further into the internal cone of the coupling
element which, because of its resilient, inward, radial
deformation, bears fully upon the pipe. If the pipe is smaller
in relation to the nominal diameter of the clamping ring,
and/or if the radial elasticity of the pipe i5 greater, the
unslotted longitudinal section may also be deformed
plastically, i.e. it may be permanently constricted. When the
unslotted longitudinal section is constricted, the annular ribs
thereon dig into the outside of the pipe and ensure a
satisfactory seal between it and the clamping ring. On the
outside, the very slender conical surfaces of the unslotted
longitudinal section of the clamping ring and of the coupling
element, ensure very good sealing between them as they bear
against each other, with no need for additional sealing
elements in the form of O-rings.
During this procedure, the turns of the clamping ring
adjacent the unslotted longitudinal section gradually enter an
axial area of the coupling ring where they not only bear firmly
upon the pipe with theix internal surfaces, but where their
external conical surfaces bear firmly upon the internal conical
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surface of the coupling element. The annular ribs on the
insides of the turns of the clamping ring dig into the outside
of the pipe. In the case of the turns adjacent the unslotted
longitudinal section of the clamping ring the wall thickness
increases constantly towards the rear end, and in these turns
the moment of resistance to bending also increases constantly
and progressively. The result of this is that, under the
action of the peripheral force arising when the coupling screw
or coupling nut on the rear side of the clamping ring is
tightened, the turns of the slotted longitudinal section bear
with decreasing intensity upon the pipe, and the annular ribs
thereon accordingly dig, with decreasing intensity, into the
wall of the pipe. The pipe is thus clamped and held over the
entire length of the clamping ring. However, there is no local
mechanical overstressing of the pipe at any point in the axial
area of the clamping ring. Since the depth to which the
annular rings dig in decreases towards the rear end of the
clamping ring, the ribs cause no unwanted notch-effect at the
transition to the free section of pipe outside the clamping
ring. As a result of the large number of annular ring, or
annular-rib sections, digging more or less deeply into the
outside of the pipe, the pipe is prevented from being pulled
out o~ the coupling by the pressure exerted by the fluids in
the pipeline system.
Since there are no sealing elements made of elastomeric
materials, no ageing of the seals can occur. Since a greater
length of pipe end is clamped, with correspondingly improve
distribution of radial and axial clamping and retaining forces,
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local overstressing of the pipe n~ed no-t be ~eared. A clamped
pipe connection of this kind thus acquires a fatigue strength
at least approaching that o~ the pipe outside the joint, if not
equalling it. This is far greater than the fatigue strength
to be expected with conventional clamped pipe connections.
Another advantage of this clamped pipe connection is
that the unslotted longitudinal section of the clamping ring
has the least wall-thickness and is therefore easily deformed,
even with a closed ring. Because of this, and of the great
elasticity of the turns in the slotted area of the clamping
ring, the thread for the coupling screw or coupling nut may be
relatively coarse. It is even possible to use the thread
normally used with metal fittings for the relevant pipe
diameter. If necessary it is possible to screw a normal drain
plug into the coupling element, or to screw a fitting having
a normal pipe thread thereto. This eliminates the need for
adapters with different types of thread.
In one configuration of the clamped pipe connection
according to this invention, the production of spiral slots is
~0 facilitated by making it possible to clamp the clamping ring
at both ends. The unslotted longitudinal section also prevents
the final turn from running out to a pointed end which, because
of the decreasing moment of resistance to bending, would be
more exposed to the constricting action of frictional contact
with the coupling screw or coupling nut. This also prevents
sharp points at the rear ends of the clamping rings which could
cause injury when handled, especially if the points have been
inadvertently bent. The cylindrical external surface of the
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unslotted longitudinal section prevents the latter from
becoming jammed in the external cone o the coupling element,
before the remaining parts of the clamping ring have been
pushed far enough into the internal cone of the coupling
element.
One form of the clamped pipe connection makes it
possible to achieve a balanced relationship between axial
displacement and axial displacement force, on the one hand, and
adequate radial and axial clamping force, on the other hand.
This applies more particularly to GFR pipe which can be
produced with relatively small dimensional tolerances. In the
case of pipes made entirely from one thermoplastic synthetic
material, which usually have larger dimensional tolerances, it
may be desirable to make the angle of inclination of the
internal conical surface on the coupling ring larger, up to
about 10. Reducing the angle of inclination of the external
conical surface of the clamping ring ensures that the increase
in the angle of inclination of a surface enclosing the clamping
ring, such as occurs when the turns of the slotted longitudinal
section are pushed together, is again compensated for and is
adjusted to the constant angle of inclination of the internal
conical surface of the coupling element.
Another configuration of the clamped pipe connection of
this invention ensures that, when the coupling screw or
coupling nut is tightened, the annular ribs on the clamping
ring dig sufficiently far into the outside of the pipe, not
only sealing it well to the outside but also holding it
mechanically. On the other hand, and especially in the case
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of GFR pipes, the glass-fibre reinforcing is not cut through,
at least not detrimentally. The vertical front sides of the
annular ribs ensure very great resistance by the clamped pipe
to being pulled out. The rounding of the rear sides ensures
that the material on the outside of the pipe is not displaced
too much to the side and is not thereby detached from the
underlying layers of material.
The configuration of the clamped pipe connection also
ensures satisfactory clamping of the slots of the central
longitudinal section and ade~uate stabilizing of the turns with
central guidance.
The configuration of the clamped pipe connection further
ensures a balanced relationship between secure clamping and
retention of the pipe and restriction of the overall length of
the connection.
The clamped pipe connection according to this invention
ensures that the annular ribs are strong enough to penetrate
into the outside of the pipe and have adequate resistance to
bending in order to withstand forces seeking to pull the pipe
out.
Furthermore the clamped pipe connection of this
invention makes it possible for a corrosion protection agent
to protect the clamping ring, specifically or generally
prophylactically, at the ends and at the stepped section,
against corrosive attack by fluids or by the contents thereof.
This makes it possible to protect a brass clamping ring from
dezincificati~n, so that there is no need to use a special
material for the clamping ring in the presence of either very
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pure fluids or very aggressive fluids. The stepped part of the
exkernal conical surface on the unslotted longitudinal section
of the clamping ring serves to take up the corrosion protection
agent with a layer thickness preferably of o.l mm and, when the
clamping ring is slid, and above all pressed, into the external
cone of the coupling housing, the coating of corrosion
protection agent is not shaved off. The groove at the end of
the stepped section serves to take up the amounts of corrosion
protection agent which project from the geometrical boundary
of the external conical surface and are therefore pushed away
by the pressure of the clamping ring. The sharp edged
transition between the rear wall of the groove and the
unstepped external conical surface ensures that any corrosion
protection agent adhering -to the internal conica~ surface of
the coupling element is shaved off when the clamping ring is
pressed in, so that the agent cannot impair the uniformly close
fit of the unstepped section of the unslotted longitudinal
section of the clamping ring. Since the end of the spiral slot
is secured at a certain distance from the groove, this ensures
2~ an adequately wide supporting surfacs for the unslotted
longitudinal surface of the clamping ring upon the inkernal
conical surface of the coupling element which provides external
sealing of the clamping ring. In the developm~nt of the
clamped pipe c~nnection the corrosion protection agent may be
applied relatively easily and reliably. ~he choice of the
corrosion protection agent depends upon circumstances at the
point o~ use.
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When glass-fibre reinforced plastic is used for the
clamping ring and the coupling element, these parts have the
same, or at least similar, properties as regards resilient
deformation and/or changes in shape and dimensions. In this
way, the behaviour of the clamped pipe connection, and that of
the pipe coupled thereto, are approximated. It is also
possible to ensure that the annular ribs on the inside of -the
clamping ring have relatively high dimensional stability,
permitting reliable penetration and digging into t~e outside
of the pipe to be secured, the outer layer of which usually
has relatively little strength.
The clamped pipe connection may be configured to ensure
that the pipes may be pushed into the connection easily and
without damaging either the clamping ring or the pipe itself,
if the connection is already preassembled and the clamping ring
is seated loosely in the internal cone of the coupling element
and is held and covered by the partly screwed-in coupling screw
or the partly screwed-on coupling nut.
The clamped pipe connection according to this invention
makes it easier to insert the coupling ring into the coupling
element, especially since, because of the spiral slot, the
clamping ring has less dimensional stability than an unslotted
ring and is therefore more readily subjected to slight changes
in shape during storage and handling.
In another configuration of the clamped pipe connection,
when the coupling screw or coupling nut is tightened, the
locking ring placed between it and the clamping ring is
deformed in such a manner that its outer edge digs into the
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matching cylindrical surface of the coupling element and the
locking ring is locked to some extent to the coup]ing element,
so that the clamping ring, which clamps and seals the pipe~ is
held in its clamping and sealing position if the coupling screw
or coupling nut, for any reason whatsoever, becomes loose or
yields in some other way. This conEiguration may therefore be
considered for pipe connections which either need never be
released or which require greater safety against becoming
disconnected and/or leaking~ This applies above all to covered
pipelines which are not easily accessible at a later date.
In the case of yet another configuration of the clamped
pipe connection of this invention, the radial depth of the
recesses between the annular ribs follows the depth of
penetration of the annular ribs into the outside of the pipe,
which decreases from the front to the rear end of the clamping
ring. Thus in the central and rear part of the clamping ring,
the peripheral surface of the recesses guiding and retaining
the clamped pipe is also made use of, so that the pipe is not
hollow in this area between the annular ribs. This prevents
a possible notch effect by the annular ribs, especially in the
rear part of the clamping ring when the clamped pipe is
subjected to bending. This applies in particular to designs
of the clamping ring in which there is an unslotted
longitudinal section at the end which has a smooth internal
surface.
Using a coupling nut instead of a coupling screw makes
it possible for the coupling element to be considerably shorter
because the thread for it can be located on the outside of the
LCM:HWR 14
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coupling element in approximately the same longitudinal section
as that upon the inside of which the internal conical surface
for the clamping ring is located. In addition to this, i-t is
usually possible also to reduce the outside diameter of the
coupling element, since the internal thread for the coupling
screw has a larger inside diameter than the internal conical
surface must have with its large diameter. The configuration
of such a connection, with the collar-like extension of the
coupling nut, permits longer axial travel of the rear end of
the clamping ring since, in case of need, the extension may be
moved into the coupling element. This reduces the dependency
upon close production tolerances in thesè connections, above
all in the case of the pipe.
In another configuration of the clamped pipe connection
a shoulder ensures that a pipe, inserted into the connection,
is inserted as ~ar as is necessary to achieve reliable clamping
and sealing. This also prevents the pipe from being
inadvertently pushed beyond the correct position and into the
area of the adjoining clamped pipe connection, in which case
the pipe to be inserted can no lon~er reach its correct
position. Since a cylindrical surface adjoins the shoulder,
and matches the outside diameter of the pipe, the pipe inserted
into the connection is centred accurately in the coupling
element itself, i.e. independently of the random axial and
radial position of the clamping ring in the coupling element.
The internal conical surface adjoining the cylindrical surface
facilitates insertion of the pipe into the longitudinal section
with the cylindrical surface and, at the same time, prevents
LCM:HWR 15
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the pipe from belng halted before it reaches the cylindrical
surface. This configuration is always used in preference to
the basic design when the resulting extension of the basic
element does not prevent its use.
Plastic pipes having greater resiliency, e.g. pipes made
of a thermoplastic synthetic material, may be joined reliably
together or connected to a fitting. In this case the axial
extension of the coupling element acts as a supporting collar
for the end of the pipe which supports itself radially, with
the matching recess on its inside, upon the supporting collar.
This ensures that, when the coupling screw or coupling nut is
tightened, the wall of the pipe cannot yield inwardly under the
action of radial force, that the annular ribs in the unslotted
longitudinal section of the clamping ring can diy into the wall
of the pipe, and that the pipe is reliably sealed. This also
holds the pipe securely.
The invention is described in greater detail
hereinafter, in conjunction with a plurality of embodiments
illustrated in the drawing attached hereto, wherein:
Fig. 1 shows a longitudinal section through a pipe
coupling having two clamped pipe connections, each with a
clamping ring;
Fig. 2 shows a longitudinal section through one of the
clamping rings;
Fig. 3 shows a detail of the clamping ring according to
Fig. 2, on an enlarged scale;
~ig. 4 shows part of a longitudinal section through
another embodiment of the clamped pipe connection;
LCM:HWR 16
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Flg. 5 shows a part of a longitudinal section through
a modified embodiment of the clamping ring, to an enlarged
scale;
Fig. 6 shows a part of a longitudinal section through
a further embodiment of the clamped pipe connection, in the
preassembled condition:
Fig. 7 shows part of a longitudinal section through the
embodiment accordin~ to Fig. 6, in the assembled condition;
Fig. 8 is in part a longitudinal section through, and
in part a side elevation of, an embodiment of the clamped pipe
connection comprising a coupling nut;
Fig. 9 is in part a longitudinal section through, and
in part a side elevation of, an embodiment of the clamped pipe
connection comprising a supporting collar.
Pipe coupling 10, shown in Fig. 1 unites two pipes ll
and 12. These two pipes are made of a composite material, to
wit glass-fibre reinforced plastic, for which reason they will
be referred to hereinafter as GFR pipes.
Pipe coupling 10 comprises, for each pipe 11,12 a
clamped pipe connection 13,14 each connection being arranged
at one end of the pipe coupling in mirror-image of the other.
The following comments regarding clamped pipe
connections 13,14 also apply accordingly to other types of pipe
couplings, such as a T-shaped design, or to a wide variety of
fittings equipped with at least one clamped pipe connection
corresponding to connections 13 and 14.
Each of the two connections 13 and 14 comprises a
coupling housing 15,16 of the same design, each forming part
LCM:HWR 11
of a one-piece basic element 17 which is made of metal, more
particularly of brass. However, consideration may also be
given to other materials normally used in pipeline systems.
Basic element 17 is an elongated hollow body of approximately
cylindrical configuration. An internal shoulder 18 is located
longitudinally centrally of basic element 17, i.e. at the inner
end of each coupling element 15,16. The internal, cylindrical,
peripheral surface thereof has an inside diameter which is
preferably no smaller than that of GFR pipes 11,12 to be
united. Internal shoulder 18 constitutes, with its two flat
end surfaces which are at right angles to the longitudinal axis
of basic element 17, a stop for the ends of GFR pipes 11,12,
thus ensuring that the two pipes can be inserted only as far
as the middle of basic element 17 and cannot be pushed on into
the area of the other connection.
In view of the fact that connections 13,14 are mirror-
images of each other, the following explanation is limited to
right hand connection 14 in Fig. 1, although it also applies
to connection 13.
In additional to coupling housing 16, clamped pipe
connection 14 comprises a coupling screw 19 and a clamping ring
20.
Coupling element 16 comprises two longitudinal sections
21,22. The internal surface of longitudinal section 21
adjoining internal shoulder 18 is formed by a very slender
internal conical surface 23 running at an angle of at least
4.5 to the longitudinal axis of coupling element 16. Second
longitudinal section 22 of coupling element 16 has a
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cylindrical internal surface equipped with an internal thread
24 matching thread 25 of coupliny screw 19. These threads are
generally cylindrical pipe threads such as are common in pipe
line systems consisting of metal pipes.
The outer end of coupling screw 19 has an external
hexagon. The inner end of the screw has a thread-free
cylindrical neck 26, the free end of which forms a flat
supporting surface 27, running at right angles to the
longitudinal axis of coupling element 16, for engaginy clamping
ring 20. At least in the vicinity of its end surface, the
outside diameter of neck 26 is designed in such a manner that,
in the operating condition, i.e. when coupling screw 19 is
tightened, it does not touch internal conical surface 23 of
coupling element 16. The length of neck 26 is governed mainly
~y the dimensional tolerances and by the deformability of pipes
11,12 which are to be united by pipe coupling 10.
Like coupling element 16, coupling screw 19 is made of
metal, again more particularly of brass. The same applies to
clamping rings 20.
Clamping ring 20 has a cylindrical inside 28. The
outside thereof is in the form of a very slender 2xtsrnal
conical surface 29. The angle of inclination thereof, in
relation to the longitudinal axis of clamping ring 20, is
somewhat smaller, up to 1 smaller, than the angle of
inclination of internal conical surface 23 of coupling element
16.
The end surface having the larger conical diameter, at
the rear end of clamping ring 20, serves as a locating surface
LCM:HWR 19
1.3~793~
31 for coupling screw 19, i.e. for locating surface 27 thereof.
For this reason, surface 31 on clamping ring 20 is also flat
and at least approximately at right angles to the longitudinal
axis of the ring. At the front end of clamping ring 20, the
end having the smaller conical diameter end surface 32 is also
flat and at least approximately at right angles to the
longitudinal axis of the said clamping ring.
The inside diameter of clamping ring 20 is at least
approximately equal to the outside diameter o pipes 11,12 to
be wlited. This inside diameter ~ill be referred to
hereinafter as the nominal width of pipe coupling 10.
The axial length of clamping ring 20 is preferably at
least approximately 0.5 times its nominal width.
As may be gathered from Fig. 2, the central part of
clamping ring 20 carries a helical, radially continuous slot
referred to hereinafter as spiral slot 33. The direction of
the turns in spiral slot 33 is opposite to that of the turns
of internal thread 24 in coupling element 16 and to that in
thread 25 in coupling screw 19. Spiral slot 33 preferably has
four full turns, so that the slotted longitudinal section of
clamping ring 20 is divided approximately into three adjacent
full turns 34. Spiral slot 33 terminates, in the axial
direction, both at the rear and at the front end of clamping
ring 20, at a certain distance from the end surface of the
clamping ring, so that a longitudinal section 35 at the rear
end, and a longitudinal section 36 at the front end, remain
unslotted. The axial extension of these unslotted longitudinal
sections 35,36 amounts, at least approximately, to 0.1 times
LCM:HWR 20
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the nominal width sf clamping ring 20. The pitch of spiral
slot 33 thus amounts, at least approximately, to o.l~ times the
nominal width of clamping ring 20.
Unslotted longitudinal section 35, at the rear end of
clamping ring 20, as distinct from the remainder of the
clamping ring, has a cylindrical outer surface which extends
axially at least as ar as the beginning of spiral slot 33, but
which may also extend therebeyond.
The illustration in Fig. 3, to an enlarged scale
includes a modification to the normal clamping ring according
to Fig. 2 in that, in the vicinity of the unslotted front
longitudinal section 36, in a section 38 adjoining front end
surface 32, the outer surface is stepped inwardly by an amount
at least approximately 0.1 mm in diameter. The axial extension
of this stepped section 38 preferably amounts to 2.0 mm. ~s
another part of this modification, located at the end of
stepped section 38 is a peripheral groove 39 which is, at least
approximately, 0.1 mm in depth in relation to stepped section
38 and is at least approximately 0.5 mm in width. The rear
wall of groove 39, farthest away from front end surface 32,
adjoins with a sharp edge, external conical surface 2~ of the
clamping ring.
~ f, in the case of clamping riny 20, the modified design
comprising stepped section 38 is selected, care must be taken
to ensure that spiral slot 33 terminates in the axial direction
at least approximately 0.5 mm in front of groove 39, in order
to leave, at front unslotted longitudinal section 36 of
clamping ring 20, an unstepped section of external conical
LCM:HWR 21
~ 3 ~
surface 29 0.5 mm in length and extending over the entire
periphery of the clamping ring between spiral ~lot 33 and
groove 39.
In the modified embodiment of clamping ring 20, stepped
section 38 serves to take up a corrosion protection agent which
is applied beyond steppPd section 38 to the whole of end
surface 32. When a clamping ring of this kind is slid into
coupling element 13, even when coupling screw 19 is tightened,
at least some of the corrosion protection agent remains, in the
vicinity of stepped section 38, adhering to the outer surface,
it being possible for the corrosion protection agent displaced
therefrom to collect in groove 39. Examples of corrosion
protection agent are polyethylene, polytetrafluoroethylene,
polyamide and also other thermoplastic synthetic materials, the
choice of which depends upon the fluid, ox the contents of the
fluid, against which the front end of clamping ring 20 is to
be protected. The protection agents are preferably applied to
the areas to be protected, in the original powder form, by the
vortex-sintering prosess.
As already indicated in Fig. 2, and shown still more
clearly in Fig. 3, the cylindrical inside of clamping ring 20
comprises a series of peripheral annular ribs 41, closed per
se, each arranged in a plane at right angles to its
longitudinal axis. The radial height of annular ribs 41 is at
least approximately 0.4 mm~ The axial spacing (or division)
between them is preferably between 1.2 and 1.4 mm, the small
spacing being used with shorter rings and smaller nominal width
and the larger spacing with longer clamping ribs and larger
LCM:HWR 22
~L 3 ~ 3
nominal width. Front flanks 42 of annular rigs 41, facing end
surface 32, are at lQast approximately at right angles to the
longitudinal axis of clamping ring 20. From the sharp annular
cutting edge, to the kase of the front flank of next annular
rib 41, rear flanks 43 are rounded at least approximately
constantly. This applies above all to the smaller longitudinal
spacing of annular ribs 41. With wider spacing, and above all
with greater nominal width, it may be desirable to allow the
curvature of rear flank 43 to run out before the next front
flank into a cylindrical surface.
The inside of longitudinal section 35 is chamfered
conically at the rear end of clamping rin~ 20. The angle of
inclination of chamfer 44, in relation to the longitudinal axis
of clamping ring 20, amounts to about 30. The axial extension
of chamfer 44 amounts to about 1.0 mm. The cham~er makes it
easier to push the pipe to be coupled into the clamping ring.
It is preferable for pipe coupling 10 to be delivered
in a pre-assembled condition. To this end, a clamping ring is
inserted loosely into each coupling element 15,16 and coupling
screw 19 is screwed so far into coupling element 16 that its
locating surface 27 bears against locatiny surface 31 of
clamping ring 20. In this connection, turns 34 of clamping
ring 20 must not bear against each other - in other words
spiral slot 33 must still be at least partly open. Pipes 11,12
to be united are pushed into relevant coupling element 15,16
until their end surfaces bear lightly against internal shoulder
18. As soon as coupling screw 19 is screwed into coupling
element 16, turns 3~ of clamping ring 20 come together,
LCM:HWR 23
~ 31~8.~
whereupon front unslotted longitudinal section 34 of clamping
ring 20 is displaced axially along internal conical surface 23
of coupling element 16. Because of its slight wall thickness,
it now constricts, initially resiliently, but subsequently also
plastically. In accordance with this constriction, annular
ribs 41, on the inside oE longitudinal section 36, cut into
pipe 12 and into the outer layer of the GFR pipe. As the axial
resistance increases when front unslotted longitudinal section
36 is pressed in, so does the frictional force between locating
surface 31 on the clamping ring and locating surface 27 on
coupling screw 19. As a result of this, turns 34 of clamping
ring 20, adjoining rear unslotted longitudinal section 35, are
carried along from front to rear to an increasing degree, so
that the turns constrict and annular ribs 41, located on the
inside thereof, also dig into the outside of the GFR pipe to
an increasing degree. As soon as this procedure has been
completed, the end section of pipe 12 is secured and sealed to
pipe coupling 10.
Up to now, the explanations have covered the uniting of
GFR pipes which can be produced to relatively small dimensional
tolerances and which have relatively slight resilient
elongation. Pipes made exclusively from a thermoplastic
synthetic material, i.e. which lack glass-fibre reinforcement,
have not only larger dimensional tolerances but also greater
elongation.
In order to unite such pipes, it may be desirable to use
a modified design of the clamped pipe connection in which the
angle of inclination of the internal conical surface at the
LCM:HWR 24
~3~7~
coupling housing is up to 10 larger, so that the internal
conical surface, and the internal thread, need not be
excessively long. Because of the larger angle of inclination
of the two conical surfaces, it may al50 be desirable to use
a fine thread, instead of the normal pipe thread, between the
coupling element and the coupling screw so that, in the case
of the coupling screw, the ratio between the peripheral force
applied to the external hexagon and the advancing force is
increased in order to equalize the higher radial force when the
front unslotted longitudinal section oE the clamping ring is
constricted.
According to another modification of the clamped pipe
connection, both the coupling element and the clamping ring are
made of glass-fibre reinforced plastic. This may be desirable,
even necessary, if the fluid flowing through the pipeline
system does not permit the use of metal or suggests a change
to plastic parts. In the case of composite GFR materials, the
innermost wall layer exposed to the fluid may be adapted,
within wide limits, to the requirements of the fluid, with no
need for any substantial change to the remaining layers of the
composite material.
The transition to a GFR material may also be indicated
if, especially when there are large numbers of joints and/or
fittings in the pipeline system, the overall weight of the
system, or even only the "weight of metall' will be very high,
or if, for other reasons, it is desirable or necessary to
reduce the proportion o~ metal in thè pipe syskem.
LCM:HWR 25
~ 7~
In the case of a clamped pipe connection made of GFR
material it is a great advantage for the glass-fibre
reinforcement in the clamping ring, in the vicinity of the
ànnular ribs, to be at least thicker or, better still, to be
aligned completely in the peripheral direction. It is also
desirable to use larger amounts of glass-fibre in the material
of the annular ribs than in the material of the remaining parts
of the clamping ring. This imparts to the annular ribs
increased dimensional stability which, in spite of the use of
GFR, allows them to dig far enough into the outside, i.e. the
outer layer, of the pipe to be coupled, thus sealing it and
holding it reliably.
Fig. 4 shows another embodiment of a clamped pipe
connection 45 in which the coupling housing 46 is modified to
some extent in relation to coupling housing 16 in the basic
version.
Adjoining shoulder 47 or, to be more precise, adjoining
end surface 48 thereof, is a cylindrical surface 49 and then
an internal conical surface 50. The axial extension of surface
49 is preferably not less than 2 mm. The inside diameter
thereof is at least approximately equal to, or slightly greater
than, the nominal width of clamped pipe connection 45 or of the
outside diameter of pipe 1~. Cylindrical surface 49 acts as
a guide for the front end of pipe 12, especially if it is
inserted into preassembled connection 45~ This ensures that
the front end of pipe 12 is guided centrally of the
longitudinal axis of coupling housing 46. Internal conical
surface 50 serves as a lead-in for the front end of pipe 12.
LCM:HWR 26
~3~7 ~
The angle of inclination of the internal conical surface 50 is
therefore preferably between 30 and 45. Adjoining this lead-
in cone, in the case of pipe connection 45, is internal conical
surface 51 for clamping ring 20 which is of the same design ~s
corresponding internal conical surface 23 in coupling housiny
16 (Fig. 1). The remaining parts of coupling housing 46, like
coupling screw 19, are the same as the corresponding parts in
the design according to Fig. 1.
Fig. 5 shows a clamping ring 52 which is a modification
of clamping ring 20. In central longitudinal section 54 of
clamping ring 52, slotted by spiral slot 53, the radial depth
of annular recesses 55, between each two annular ribs 56,
decreases from the front end of longitudinal section 54,
towards its rear end, from a maximum value to zero. The
maximum value of the depth of recesses 55 is at least
approximately equal to the radial depth of corresponding
recesses 57 in front unslotted longitudinal section 58 of
clamping ring 52. Since the radial depth of recesses 55, at
the rear end of slotted longitudinal section 54, has reached
the value of zero, there are no internal recesses in rear
unslotted longitudinal section 59 of clamping ring 52, and
therefore also no annular ribs. This interior is therefore a
smooth cylindrical surface 60.
FigsO 6 and 7 show another embodiment of a clamped pipe
connection 61. In this case, a cylindrical surface 64 adjoins
the inside of coupling element 62 at the outer end of internal
conical surface 63 for clamping ring 20, the inside diameter
of the cylindrical surface 64 being larger than the outside
LCM:HWR 27
''
'~ :
13~79~
diameter of the rear end of the clamping ring, and ,ls thus
larger than the outside diameter of the unslotted rear
longitudinal section 35 of the clamping ringO The inside
diameter of cylindrical surface 64 is matched to internal
conical surface 63 in such a manner that transition 65, between
internal conical surface 63 and cylindrical surface 64 is
located within the longitudinal section of coupling element 62
which takes in clamping ring 20 after coupling screw 19 has
been tightened (Fig. 7). The axial extension of cylindrical
surface 64, starting from transition 65, is such that/ when
clamping ring 20 is inserted in the tightened condition, the
cylindrical surface extends beyond the rear end of clamping
ring 20 (Fig. 6).
A locking ring 66 is inserted or interposed between rear
end surface 31 of clamping ring 20 and front end surface 27 of
coupling screw 19. The inside diameter of locking ring 66 is
no smaller than the nominal width of clamping ring 20 or, even
better, is no smaller than the inside diameter of coupling
screw 19. Locking ring 66 has two end surfaces 67,68 running
parallel with each other. Locking ring 66 is made conical so
that its two end surfaces 67l68 are in the form of the surface
of a truncated cone. The angle between truncated conical end
surfaces 67l68 is between 60 and 75l preferably about 68.
With locking ring 66 in its unbraced condition of rest (Fig.
6), peripheral surface 69 thereof is a cylindrical surface in
relation to the centreline of the locking ring. Above all,
peripheral edge 70, between peripheral surface 6~ and inner end
surface 68, has a sharp edge.
LCM:HWR 28
- .
When clamped pipe connection 61 is tightened, lockin~
ring 66 is first pressed by coupling screw 19 against clamping
ring 20 and is pushed, therewith, for a certain distance, into
coupling element 62 (Fig. 7). As soon as the front end of
clamping ring 20 has contracted to such an extent that it
clamps pipe 12 and seals it, and the resistance to displacement
at the rear end of the ring has therefore risen to a higher
value, locking ring 66 is pressed flat between rear end surface
31 of clamping ring 20 and front end face ~7 of coupling screw
19 (Fig. 7). Peripheral surface 69 is thus pressed outwardly
and peripheral edge 70 thereof digs into cylindrical surface
64 of coupling element 52. Locking ring 66 is thus to a
certain extent locked to coupling element 32. Even if coupling
screw lg were to become loose, locking ring 66 would ensure
that clamping ring 20 cannot expand axially since the axial
force exerted by it would cause the locking ring to dig more
deeply into cylindrical sur~ace 64 of coupling element 62.
Clamped pipe connection 61 may be considered for pipe
connections which will not be disconnected again once they have
been united, or even when there i5 a requirement for prevention
of inadvertent release of the connection for any reason
whatsoever.
Fig. 8 shows a pipe coupling 71 which is a modification
of previously explained pipe coupling such as those of Figs.
1 and 4 in that the two connections 72,73 are e~uipped, not
with coupling screws, but with two coupling nuts 74. Thus the
longitudinal sections, which in the case of coupling housing
46 comprise the intarnal threads for the coupling screws, are
LCM:HWR 29
~317~
missing from coupling housing 75. Apart from this, the
interior of coupling housing 75, in the vicinity oE clamping
ring 20, is of the same design as coupling housing 46 ~Fig. 4).
Reference is therefore made to the explanation covering the
latter housing.
In coupling housing 75, internal conical surface 76 for
clamping ring 20 has an axial length which is shorter than
internal conical surface 51 on coupling housing 46. Internal
conical surface 76 is so short that when clamping ring 20 (Fig.
8) is in its operating or clamping position, its rear unslotted
longitudinal section 35 projects partly from coupling housing
75.
External thread 77 for coupling nut 74 is arranged
approximately in the same longitudinal section as internal
conical surface 76 but on the outside of coupling housing 75.
Between the two longitudinal sections with external thread 77
for the two coupling screws 74, coupling housing 75 comprises
a longitudinal section 78 which is provided with wrench flats
79 in tha form of a hexagon or an octagon.
Coupling nut 74 carries a circular shoulder 81, the
inside diameter of which is no smaller than the nominal
diameter of pipe 12 to be coupled and is preferably even
slightly larger. Adjoining the intexnal end surface of
shoulder 81r in the axial direction, is a collar-like extension
82, the inside diameter of which is the same as that of
shoulder 81. .The outside diameter of extension 82 is no larger
than the outside diameter of rear unslotted longitudinal
section 35 of clamping ring 20. The axial length of extension
LCkI:HWR 30
~ 3 ~L r~ ~ ~ r~
82 is generally between 0.5 and 2.0 mm. The end surface of
collar-like extension 82 forms locating surface 83 for clamping
ring 20. Collar-like extension 82 provides longer axial
actuating travel for cou~ling nut 74 since, in case of need,
extension 82 may be moved into coupling housing 75. This
enables coupling nut 74 to apply an axial force to the rear
locating surface of clamping ring 20 when rear longitudinal
section 35 of clamping ring 20 is already completely submerged
in coupling hose 75. This condition could occur if the
production tolerances of all co-operating parts, especially
those relating to the diameters of internal conical surface 76,
clamping ring 20 and pipe 12, were to combine adversely.
Fig. 9 shows another modification of the clamped pipe
connection. Externally, pipe coupling 85 is similar to pipe-
coupling 71 (Fig. 8). Each clamping connection also comprises
a coupling nut 88 similar to coupling nuts 74. However,
coupling housiny ~9 has a modified central longitudinal
section, as compared with coupling housing 75. The reason for
this is that pipe coupling 85 is intended for plastic pipes
91,92 which are made of a thermoplastic synthetic material.
Because of the low strength of this material, such pipes have
much thicker walls than GFR pipes 11,12.
The inside of central longitudinal section 93 of
coupling housing 98 carries a shoulder 94, the inside diameter
of which is no smaller than the inside diameter of pipes 91,92.
On each end surface of shoulder 94, an external annular area
has an at least approximately flat end surface 95 which is at
right angles to the longitudinal axis of coupling housing 89.
LCM:HWR 31
Moulded to each side of the inwardly adjoining inner annular
area is an axial extension 96. Inner peripheral surface 97 of
extension 96 is an at least approximately cylindrical surface,
the inside diameter of which is equal to the inside diameter
of shoulder 94. External peripheral surface 98 is in the form
of a truncated cone, the surfaces of which are at an angle of
between 20 and 45~ to the longitudinal axis of coupling housing
89. In Fig. 9, this angle is 30.
Each of the two pipes 91,92 is provided, on the inside,
at the end co-operating with pipe coupling 85, with a recess
99 matching axial extension 96 and thus appearing as the
surface of a hollow truncated cone.
As may be gathered from Fig. 9, the outside diameter of
extension 96, at the transition to shoulder 94, i.e. at its
thickest point, has an outside diameter smaller than that of
pipes 91,92. This leaves a flat circular end surface loo at
the ends of pipes 91,92 externally of truncated conical recess
99 .
In order to allow recess 99 in pipe 91 or 92 to co-
operate correctly with extension 96 on coupling housing 89, andto allow extension 96 to act as a supporting collar for the
relevant pipe, it is desirable, when producing recess 99,
probably with a conical counterboring tool, to machine end
surface 100 at the same time. This ensures that end surface
100 is smooth and flat an that the sawing of the pipe has not
left any irregularities which may prevent the end of the pipe
from being pushed in until recess 99 bears against extension
96 to shoulder 94. The simplest way of accomplishing this is
LCM:HWR 32
13~7 ~ ~3 ~
to combine the conical counterboring tool with a flat
counterbore, so that recess 99 is produced and end surface 100
is machined simultaneously. In this connection, care must be
taken to ensure that the depth of recess 39 is no greater than
the length of extension 96 so that, when the pipe is inserted,
recess 99 seats upon extension 96 before end surface 100 comes
up against shoulder g4.
In the example of embodiment of clamped pipe connections
according to Fig. 9, the end of the pipe is centered internally
by conical extension 96. This makes it possible to dispense
with the external guiding surface which is formed, in the
example according to Fig. 4, by cylindrical surface 49 in front
of internal conical surface 50. In khis respect the example
according to Fig. 9 corresponds to the example according to
Fig. 1.
Instead of a truncated conical peripheral surface 98,
the axial extension to shoulder 94 may also have a cylindrical
peripheral surface, but it is desirable for the outer edge of
the free side of the extension to be chamfered, thus providing
a kind of lead-in cone. The recess on the inside of the pipe
must also be made cylindrical in order to match the cylindrical
shape of the extension. However, the cylindrical shape of
these two surfaces is more sensitive to production tolerances
in diameter dimensions.
LCM:H~R 33
1 317~38~
LI8T OF REFERENC13 NUMBRALEI
lo pipe-coupling 55 recesses
11 GFR pipe 5S annular ribs
12 GFR pipe 57 recesses
13 clamped pipe connection 58 longitudinal section
14 clamped pipe connection 59 longitudinal section
15 coupling element 60 cylindrical surface
16 coupling element 6~ clamped pipe connection
17 basic element 62 coupling element
18 internal shoulder 63 internal conical surface
19 coupling screw 64 cylindrical surface
20 clamping ring 65 transition
21 longitudinal section 66 locking ring
22 longitudinal section 67 end surface
23 internal conical surface 68 end surface
24 internal thread 69 peripheral su:rface
25 screw thread 70 peripheral surface
26 neck 71 pipe coupling
27 locating surface 72 clamped pipe connection
28 inside surface 73 clamped pipe connection
29 external conical surface 74 coupling nut
31 locating surface 75 coupling housing
32 end surface 76 internal conical surface
~3 spiral slot 77 external thread
34 turns 7~ longitudinal section
35 longitudinal section 79 wrench surfaces
36 longitudinal section ~1 shoulder
37 outer surface 82 extension
38 stepped section 83 locating surface
39 groove 85 pipe coupling
41 annular ribs 86 clamped pipe connectlon
42 front flank 87 clamped pipe ~onnection
43 rear flank 88 coupling nut
44 chamfer 89 coupling housing
45 clamped pipe connection 91 plastic pipe
46 coupling housing 92 plastic pipe
47 shoulder 93 longitudinal section
48 end surface 94 shoulder
49 cylindrical surface 95 end surface
50 internal conical surface ~6 extension
51 internal conical surface 97 internal peripheral surface
52 clamping ring 98 external peripheral surface
53 spiral slot g9 recess
54 longitudinal section ~00 end surface
LCM:HWR 34
