BACKGROUND

The present invention relates to an apparatus for use in the insertion of a draw line inside 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 ofthe shuttle for the insertion of a draw line in telecommunications cables but this is not to be construed as limiting ofthe applications to which the invention in all its forms may be put.

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. There are many thousands of kilometres of such cables already laid in underground conduits, but due to the rapid increase in telecommunications 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 reserve awaiting receipt of new cables, those that are already partially filled and those that are fully occupied with cables. It is the first and second ofthe two aforesaid categories that the invention is principally concerned with. The process of inserting cables into conduits is time consuming, labour intensive and thus expensive. Existing methods of insertion of draw lines in conduits are slow, cumbersome and inefficient.

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 ofthe cable so it can be pulled through to the end ofthe length of conduit. Draw lines may be inserted in advance and simply left lying in a conduit awaiting later insertion of a cable. This is helpful to the cable installer as in this case, the draw line is already placed in the conduit in advance of the cable installation, 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

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 maintain the positive air pressure required, the entry end ofthe 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 ofthe conduit of rags and the like which must be manually held in position whilst positive pressure is delivered to the inside ofthe pipe Positive pressure is introduced into the conduit via a copper tube which is connected to a source 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 compromise to the integrity ofthe 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 ofthe parachute. The presently used parachute essentially comprises a sheet of 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 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, tangling the connecting strings in which case the string can capture the air collecting textile material ofthe parachute This means that the tangled parachute can jamb in the pipe and has to be 'fished' out ofthe conduit and the insertion 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 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

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 consuming

There are other problems with use ofthe prior art arrangements, for instance, the string ofthe 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 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 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.

THE INVENTION 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 ofthe prior art methodology referred to above 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 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,

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 ofthe 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 ofthe conduit. The leading edge of the shaft terminates in a nose cone and the leading end of each of any remaining 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 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 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 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.

The present invention will now be described in more detail according to a preferred 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 ofthe 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, Figure 5 shows a tandem shuttle with leading and trailing collectors wherein the trailing collector has by pass holes

Referring to figure 1 there is shown a shuttle 1 according to one embodiment adapted to travel along the inside of a conduit 2 under the assistance of positive air pressure from an air source (not shown) applied at an entry end ofthe pipe It will be recognised that the embodiment ofthe 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 collection cell type Thus, in the case where multiple collectors are used on one shaft element, the collectors may be the same type or a combination ofthe skirt variety and air collection cell variety Shuttle 1 comprises a generally elongated shaft 3 having a leading end 4 and a trailing end 5 In use, shuttle 1 pulls a draw line 6 from an entry end ofthe pipe to an exit end Trailing end 5 of shaft 3 includes connecting means 7 which receives the leading end of draw line 6. Connecting means 7 may comprise a simple loop to which is tied said leading end 6a ofthe 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 ofthe shuttle Intermediate the ends ofthe 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 shaft 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

generated by the air pressure, tending to rotate or tumble the shuttle compromising 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 1 1 each of which comprise a flexible material. Each of said collectors are at least partially fixed to shaft 3 Each collecting skirt 1 1 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 1 1 of shuttle 1 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 1 is then uncoupled from draw line 6 for re use.

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 ofthe pipe is achieved. This will result in the skirt or cells engaging the inner wall of conduit 2 as the skirt or cell envelopes 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 ofthe skirt or air collecting cells.

Figure 2 shows an exploded view of a double shuttle similar to the embodiment ofthe invention shown in figure 1.

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 elements 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) ofthe 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 ofthe invention

Figure 5 shows a tandem shuttle 40 comprising shaft elements 41 and 42 including thereon 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 and modifications may be made to the invention as broadly described herein without departing from the spirit and scope ofthe invention