Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SHUTTLE FOR USI~ IN INSERTION OF A DRAW LINE INTO A CONDUIT
BACKGROUND
The present invention relates to an apparatus for use in the insertion of a draw line inside
5 a conduit and more particularly relates to an air flow activated shuttle for use in effecting
that insertion. The invention will be described with reference to the use of the shuttle for
the insertion of a draw line in telecommunications cables but this is not to be construed
as limiting of the applications to which the invention in all its forms may be put.
10 PRIOR ART
Telecommunications cables are nowadays generally laid underground in specially
constructed trenches. In order to protect the cables from potential damage by water,
debris and vermin, typically, communications cables are laid inside plastic ~usually
polyvinylchloride (PVC)) conduits. ~here are many thousands of kilometres of such
15 cables already laid in underground conduits, but due to the rapid increase intelecommunications and thus the need for more cables, conceivably hundreds of
thousands of kilometres of cable will be required in the future.
There are generally three categories of installed conduits, those that are left empty in
20 reserve awaiting receipt of new cables, those that are already partially filled and those
that are fully occupied with cables. lt is the first and second of the two aforesaid
categories that the invention is principally concerned with. The process of inserting
cables into conduits is time con.c~ming, labour intensive and thus expensive. Existing
methods of insertion of draw lines in conduits are slow, cumbersome and inef~lcient.
In order to feed a cable through a conduit, it is necessary to first insert a draw line inside
the conduit which is then anchored to the leading end of the cable so it can be pulled
through to the end of the length of conduit. Draw lines may be inserted in advance and
simply left Iying in a conduit awaiting later insertion of a cable. This is helpful to the
30 cable installer as in this case, the draw line is already placed in the conduit in advance of
the cable in~t~llation, enabling the draw line to be readily attached to the leading end of
the cable which is then pulled through by the draw line. One existing method for
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insertion of a draw line in a conduit includes the use of a crude parachute to which a
draw line is connected. The parachute is inserted via an entry end into the conduit.
Pressurised air is then delivered from an air source to the parachute causing it to inflate
following which it exits the pipe taking the draw line with it. In order to m~int~in the
5 positive air pressure required, the entry end of the conduit must be sealed to prevent
escape of air through the entry end. This is presently effected in a crude manner by the
insertion in the entry end of the conduit of rags and the like which must be manually held
in position whilst positive pressure is delivered to the inside of the pipe. Positive
pressure is introduced into the conduit via a copper tube which is connected to a source
10 of pressurised air. The rags and other packing surround the copper tube. The draw line
must be loose enough to travel through or around the packing resulting in a colnpro~ise
to the integrity of the seal and in a pressure loss in the conduit via the entry end.
Another problem arising from use of the above method is that of unwanted collapsing or
bunching of the parachute. The presently used parachute essentially conlp.ises a sheet of
15 textile or like material to which is connected at peripherally located points one end of
each of multiple lengths of string or the like, each of which terminate at their other end at
a junction which also receives the leading end of the draw line.
The parachute is prone to collapsing within the conduit particularly if the air is collected
20 asymmetrically in the parachute allowing greater air by pass around one edge compared
to symmetric by pass and proper chute balance in normal operation. This imbalance can
cause the parachute to rotate, t~neline the connecting strings in which case the string can
capture the air collecting textile material of the parachute. This means that the tangled
parachute can jamb in the pipe and has to be 'fished' out of the conduit and the insertion
25 process recommenced increasing the time and labour involved in drag line insertion. In
practice this problem can occur repeatedly before successful insertion is achieved.
A further problem may occur where cables inside a partially filled conduit cross over to
form a V which then catches the parachute in the throat of the V shape. When this
30 occurs the draw line (string) continues to be air blown beyond the capture point ofthe
parachute conveying an impression to the operating personnel that the parachute is still
drawing the draw line through the conduit when in fact it has jammed. The parachute
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must be released from the capture point by pulling the draw line back through the
conduit followed by repeated attempts at insertion until the parachute successfully travels
through the pipe. This is inefficient, labour intensive and time con.~uming.
5 There are other problems with use of the prior art arrangements: for instance, the string
of the draw line comes in contact with the users hands during feeding posing a risk of
'rope burn', and the copper tube must be held in position by an operator along with the
packing rags and sponges to prevent blow out. Further, two men are usually required in
the conduit pit, one feeding the draw line and the other holding the copper air line and
10 rags in position.
In another prior art method, rods may be inserted from either end of a conduit until they
meet in the middle whereupon the conduit is cut and joined creating a further undesirable
join and thus another place through which unwanted water can penetrate. Push rods may
15 be inserted from one end of a conduit up to 100 metres. This method is cumbersome and
may lead to cable damage within the conduit particularly where a push rod engages a V
formation described above.
T~ INVENTION
20 The present invention provides an apparatus which enables the trouble free insertion of
draw lines inside conduits adapted for carrying cables such as, but not limited to,
telecommunications cables. The present invention is used in conjunction with an
apparatus which has been made the subject of a co-pending application by the present
applicant which overcomes the problems of the prior art methodology referred to above.
25 According to the present invention there is provided an air assisted self supporting
shuttle for pulling a draw line through a length of conduit.
In its broadest form the present invention comprises:
an air flow activated shuttle for pulling a draw line through a length of conduit having
30 entry and exit ends, said shuttle comprising;
a shaft having a leading end and a trailing end;
means on said trailing end which receives and retains a leading end of said draw line,
... .
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at least one air flow mitigation element attached to said shaft which at least partially
interrupts an air flow introduced into the entry end of said conduit from an air source to
said shuttle from the trailing end thereby urging said shuttle along said pipe urging said
draw line therealong and through said exit.
Preferably, the air flow retarding means comprises at least one air collector intermediate
the ends of the shaft and disposed radially about said shaft and flared in the direction of
the trailing end. Each shuttle preferably comprises at least one radial array of air
collecting cells or at least one flexible skirt.
According to an alternative embodiment air collectors may be defined by a flexible skirt
wherein the skirt of each air collector captures the air and displaces radially of said shaft
responsive to positive air pressure thereby creating a low friction fit between a flared end
of each said skirt and the internal wall of the conduit. The leading edge of the shaft
15 terminates in a nose cone and the leading end of each of any ~e~ -g collectors include
a small opening allowing positive air pressure to exit in the direction of the leading
collector to ensure that the leading collector is not starved of air.
The skirt of each collector terminates at or near said nose cone and allows positive air
20 pressure in each collector to exit via said nose cone thereby reversing the direction of air
exiting each said collector. The collectors may be individually fixed to the shaft.
In an alternative embodiment the air collector may comprise an umbrella like structure
connected to the shaft. The configuration, material and texture of the air collectors may
25 be varied according to circumstances such as the internal state of the conduit in which a
draw line is to be inserted.
According to an alternative embodiment, the shuttle may include means at the leading
end and trailing end to enable coupling of one shuttle to multiple shuttles where required.
30 Said means may comprise releasable couplings. The coupling may be effected by means
of threaded male/female profile parts on the end of adjacent shaft elements.
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The present invention will now be described in more detail according to a plel~ ed but
non limiting embodiment and with reference to the accompanying illustrations wherein;
Figure 1: shows an isometric view of a shuttle having a pair of air collectors and
inserted in a conduit according to one embodiment of the invention;
Figure 2: shows an exploded view of a shuttle comprising two shaft elements;
Figure 3: shows the shuttle of figure 2 with shaft elements coupled together;
Figure 4: shows a shuttle with one air collector comprising an array of collecting
cells,~0 Figure 5: shows a tandem shuttle with leading and trailing collectors wherein the
trailing collector has by pass holes.
Referrin~ to figure I there is shown a shuttle I according to one embodiment adapted to
travel along the inside of a conduit 2 under the assistance of positive air pressure from an
15 air source (not shown) applied at an entry end of the pipe. It will be recognised that the
embodiment of the shuttle shown in figure 1 is merely an example of a wide possibility of
shuttle configurations. For instance, a shuttle may comprise one shaft element with one
or more collectors which may be of the flexible skirt type or air colJection cell type.
Thus, in the case where multiple collectors are used on one shaft element, the collectors
20 may be the same type or a combination of the skirt variety and air collection cell variety.
Shuttle I comprises a generally elongated shaft 3 having a leading end 4 and a trailing
end 5. In use, shuttle 1 pulls a draw line ~ from an entry end of the pipe to an exit end.
Trailing end 5 of shaft 3 includes connecting means 7 which receives the leading end of
dtaw line 6. Connecting means 7 may comprise a simple loop to which is tied said2~ leading end 6a of the draw line 6. The leading end 4 of shaft 3 has mounted thereon a
nose cone 8 which provides an aerodynamic leading edge profile and contributes to the
balance and operation of the shuttle. Intermediate the ends of the shaft there are
provided two longitudinally spaced apart air collectors 9 and 10. Collectors 9 and 10
shown are each formed from a radial array of air collection cells disposed radially about
30 sha~ 3. According to an alternative embodiment one array only may be employed, with
a minimum of two diametrically disposed air collectors. Ideally the air collectors are
symmetrically disposed about the axis of shaft 3 to prevent out of balance forces
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generated by the air pressure, tending to rotate or tumble the shuttle co~ ulllising
directional stability. Ideally, the shuttle is of sufficient length to preclude the possibility
of overturning inside the conduit in which case the shuttle would jamb as occurred in the
prior art arrangements previously described.
Each of collectors 9 and 10 comprises a plurality of radially disposed air collecting skirts
11 each of which comprise a flexible material. Each of said collectors are at least
partially fixed to shaft 3. Each collecting skirt 11 is tapered from its leading to its trailing
edge.
Once draw line 6 is connected to connecting means 7 which may comprise a resilient
loop through which line 6 may be placed and the pipe end sealed, shuttle 1 is ready for
use. Once the entry end of conduit 2 is sealed, air from a source of pressurised air is
introduced into region 13 of conduit 2 whereupon collecting skirts I I of shuttle 1
15 displace radially as they collect the pressured air. This causes the shuttle to travel along
conduit 2 at an extremely fast rate until it exits the conduit pulling draw line 6 along with
it. Once draw line 6 is through the pipe, shuttle I is then uncoupled from draw line 6 for
re use.
20 Where a single air collector is used, it is preferable that the skirt (where the skirt variety
is used) or envelopes (where the collection cell variety is used) radially displaced to an
extent which maximises air collection. Thus, it is ideal that the displacement is such that
air collection from the full cross sectional area of the pipe is achieved. This will result in
the skirt or cells eng~ging the inner wall of conduit 2 as the skirt or cell envelopes
25 radially displace. Where multiple collectors are used the trailing collectors will include a
leading end opening to allow air by pass to ensure that the leading end collector is not
staved of pressurised air. Also the trailing collectors will allow by pass about the
periphery of the skirt or air collecting cells.
30 Figure 2 shows an exploded view of a double shuttle similar to the embodiment of the
invention shown in figure 1.
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Each shuttle may be threadably connected to an adjacent shuttle such that uncoupling of
a shuttle from an adjacent shuttle is a relatively simple matter. Likewise draw line 6 may
as an alternative be uncoupled and coupled by means of a threaded connection on the
trailing end 5 of shaft 3.
Figure 2 shows shaft elements 20 and 21 mutually separated. Shaft element 20 includes
flexible skirt collector 22 and shaft element 21 comprises flexible skirt collector 23.
Shaft el~melltc 20 and 21 are engageable by means of threaded male female interfitting.
Element 20 comprises threaded male profile part 24 and element 21 female profile part
25. This arrangement enables convenient adjustment to the length ofthe shuttle
according to requirements.
Figure 3 shows skirt collectors 22 and 23 as they appear when the shaft elements(concealed) of the shuttle of figure 2 are coupled together.
Figure 4 shows a single shaft element 30 with a collector 31 comprising air collecting
cells 32 according to an alternative embodiment of the invention.
Figure 5 shows a tandem shuttle 40 comprising shaft elements 41 and 42 includingthereon respectively collectors 43 and 44. Collector 43 includes in each air collecting
cell 45 an opening or openings 46 which provides an air by pass facility which prevents
leading collector 44 from pressurised air starvation.
It will be recognised by persons skilled in the art that numerous variations andmodifications may be made to the invention as broadly described herein without
departing from the spirit and scope of the invention.
