APPARATUS AND METHOD FOR CLEARING SEWERS

Abstract: Grit (G) is removed from a sewer (10) by reciprocating trawling means (13) to-and-fro along a predetermined rectilinear path in the sewer and depositing the collected grit at a location at or adjacent an extraction pump system (15) which conveys the grit to a collection hopper (37) or skip above ground level. The grit may be fluidised to assist its upward conveyance and the grit/water mixture separated in the collection hopper (37) or skip with the water being returned to the sewer (10) possibly to assist in grit fluidisation.

Description: APPARATUS AND METHOD FOR CLEARING SEWERS This invention relates to apparatus for and method of clearing sewers or other underground conduits, tunnels, excavations and chambers (hereinafter and in the claims referred to simply as "sewers") of settled grit, other small-sized debris, and sewage trapped therein (hereinafter and in the claims for convenience simply referred to as "grit"). The settlement of grit in sewers is a major problem in that the grit restricts flow of sewage along the invert of the sewer and also ' it traps sewage which ferments causing unacceptable environmental problems when sewage is discharged, for example, into estuaries. In a known method of clearing settled grit from sewers, a potable water jetting system is used to try and drive the settled grit to a manhole for extraction therethrough from the sewer by suction. This has not proved successful in that the percentage quantity of grit extracted from a given quantity of water/grit extracted is extremely small. This method would generally be used in sewers up to about 2 feet in diameter. Another known method of clearing sewers is "bucketing". In this method a bucket is dragged along a sewer length to scoop up grit. At an away hole, it is disconnected from the drag line, hoisted out of the sewer, emptied, returned to the sewer, reconnected to the drag line, returned along the sewer and the dragging operation is repeated. It can be seen that this method is slow, laborious and extremely inefficient in terms of quantity of grit extracted per unit of time. It is an object of the present invention to provide an improved apparatus for and method of removing grit from sewers which obviate or mitigate the drawbacks and disadvantages of the aforesaid known apparatus and methods. According to the present invention there is provided apparatus for removing grit from sewers comprising an extraction pump system adapted to extend from the sewer to above ground level or other •upper level for the upward conveyance of grit, and trawling means disposed within the sewer for dragging grit along the sewer to, or adjacent to, an inlet of the extraction pump system. Also according to the present invention there is provided a method of removing grit from a sewer, the method comprising pumping grit which may be fluidised out of the sewer to a collection location above ground or at an upper level, and reciprocating trawling means to-and- fro along the sewer to deposit grit in the region from which it can be pumped. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which:- Fig. 1 is a diagrammatic sectional side elevation of a sewer with the grit removing apparatus according to the present invention in position; Figs. 2 and 3 are respectively a perspective view and a side view of a grit-collecting trawling sledge according to the invention; Fig. 4 is a perspective view of a preferred modified trawling sledge; Figs. 5 and 6 are diagrammatic detail sectional views of modified trawling sledges; Fig. 7 is a perspective view of another modified trawling sledge; Fig. 8 is a detail perspective view of yet another modified trawling sledge; Figs. 9 and 10 are diagrammatic plan views of still another trawling sledge in operational and non-operational modes; Figs. 11 and 12 are diagrammatic side views of alternative trawling sledge drive means; and Fig. 13 is a diagrammatic view of an alternative extraction pump system. Referring to the drawings a large diameter sewer to be cleaned is indicated at 10 and communication to the sewer is through manholes 11 and 12. Manhole 11 will hereinafter be referred to as the upstream manhole and manhole 12 as the downstream hole. Referring to Figs. 1 to 4 of the drawings, the apparatus according to the invention comprises three main components, namely a trawling means 13, a track 14 along which the trawling means 13 is reciprocable to-and-fro, and an extraction pump system 15 for upward conveyance of grit from the sewer 10 to above ground level. The track 14 is in the form of a "ship's type" link chain 16 which is secured at each end to a fixed anchor 17 of any convenient construction, for example an extensible strut or prop (for instance Acrow props) engaging opposed regions of the sewer wall, located at or adjacent to the manholes 11 and 12. It will be manifest that the chain 16 provides a rectilinear path which can be set up with its anchors 17 to extend along a length of sewer 10 to be de-gritted and thereafter dismantled and set up in the next, and usually succeeding length of sewer 10 to be de-gritted. It is to be noted that the anchors 17 of whatever construction may be fitted with automatic water flow powered de-ragging devices. If the length of chain 16 exceeds the length of the path between the anchors 17 then the excess chain length may be stored at the upstream manhole and in any convenient manner. The trawling means 13 is in the form of a sledge 18 with a flat deck 19 and a pair of narrow side runners 20 defining a tunnel 21 open at the front of the sledge 18 but closed at the sides by the runners 20 and at the rear of the sledge 18. The closed rear end 21 of the sledge 18 allows the latter to ride over any grit G in the sewer 10 during its rearward movement. A plate 22 closes the rear end of the sledge 18 and is inclined downwardly and forwardly of the deck 19 to act as a fixed drag trawl or plate for grit collection and movement. Forwardly of the fixed drag plate 22 and pivotally connected to the underside of the deck 19 is a pair of longitudinally-spaced pivotal drag plates 23 which, when the sledge 18 is forwardly moving, are downwardly and forwardly inclined relative to the deck 19 but which, when the sledge 18 is rearwardly moving, tend to pivot upwardly about their pivot connections 24 towards the underside of the deck 19 if they encounter grit during such rearward movement. The flat deck 19 mounts at or adjacent each end a drive arrangement 25. Each drive arrangement 25 comprises a reversible air motor 26 connected by a coupling 27 to a reduction gear 28 which drives a chainwheel 29 in engagement with the chain 16. An idler chainwheel 30. is provided adjacent to but lower than its respective drive chainwheel 29. In setting up, the track constituted by the chain 16 and the trawling means 13, the chain 16 is fixed to one of its anchors 17, is threaded around one drive chainwheel 29 and its respective idler chainwheel 30, extends along and above the deck 19, is threaded around the other idler chainwheel 30 and its drive chainwheel 29, and is then secured to the other anchor 17. The chain 16 is disposed generally centrally of the sides of the sledge 18 with a drive arrangement mounted on the deck 19 at either side thereof. The reversible air motors 26 are synchronously driven by compressed air delivered from an above-ground air compressor 31 by an air delivery hose 32 connected to both motors 26. The starting/stopping and direction of rotation of the reversible air motors 26 is controlled by a valve arrangement 33 which receives its control signals (air pulses) from a pair of small diameter hoses (not shown) housed within the air delivery hose 31. The latter may also enclose another small diameter hose for delivering lubricant to the reversible air motors 26. It can, therefore, be seen that the sledge 18 can be driven along the chain 16 forwardly and backwardly with, in the forward movement, the fixed and pivotal trawl or drag plates 22 and 23 collecting and moving grit along the sewer floor to the forward end region of the chain 16 and with the sledge 18, due to its closed rear end 21 and due to the forward and upward pivotal action of the trawl or drag plates 23, riding over grit during rearward movement. The sewer 10 to be de-gritted will normally contain water to a greater or lesser degree and consequently the air hose 32 is preferably a trailing loop floating high pressure robust air hose and the compressor 31 is a high pressure compressor serving to overcome frictional losses in the air hose 32 and to ensure design pressure is supplied at the motor inlet ports. The reversible air motors 26 will be appropriately protected to prevent water entering them via submersed exhaust ports and it is preferred that the motor casings be lightly pressurised as an added precaution. The motors 26 may have vertical exhaust pipes. * To' lay the chain 16* in position a light weight rope may, if necessary, be "floated" through the sewer 10 with the assistance of a floating "drogue" if required and this rope would be used to pull a winch wire rope through the sewer 10 between the upstream manhole 11 and the downstream manhole 12 and, in turn, the wire rope would be used with a suitable roller gear to pull in the "ships type" link chain 16 which would then be tautly connected between the two struts or props 17. The trawling means 13 would then be lowered down the downstream manhole 11 and drivingly connected to the chain 16 as aforesaid. The third component of the de-gritting apparatus is the extraction pump system 15. In this embodiment, this extraction pump system 15 comprises a submersible pump 34 disposed at the bottom of the downstream manhole 12 with its inlet at the bottom adjacent to, but spaced from, the invert of the sewer 10. The submersible pump 34 has its inlet contained within a basket 35 to which is secured a high pressure water jet (not shown). This high pressure water jet is connected by appropriate hosing to a high pressure water pump (not shown) disposed above ground. The purpose of the high pressure water jet is to clear any solid debris ("rags" for example) which may block the basket 35 and consequently the inlet to the submersible pump 34. The high pressure water jet is intermittently or periodically operated. The submersible pump 34 is connected to above ground level by a hose 36 which is adapted to deliver a liquid/grit mixture into, for example, a tanker or hopper or skip or similar 37 of a vehicle 38. A return hose or pipe 39 returns the liquid from the hopper or tanker 37 within which the grit settles to the region around the submersible pump 34, which liquid assists in fluidising (liquidising) grit in the region of the submersible pump 34. Additional water may be supplied from a mains supply, if necessary, to the region of the submersible pump 34 to assist this fluidisation (liquidisation) of the grit. The submersible pump 34 may, if necessary, to assist upward suction and conveyance of as much of the collected fluidised grit as possible be moveable rectilinearly and/or laterally so that it can "sweep" the area around the bottom of the downstream manhole 12. For this purpose, the submersible pump may, for example, be mounted on a trolley or sledge connected to and moveable by the chain 16, whereof the length would be extended beyond the downstream manhole 12. Such an arrangement would impart rectilinear movement to the submersible pump 34. The hose 36 and submersible pump 34 may be pivotally or otherwise secured to the trolley or sledge to allow lateral movement to be imparted thereto by a suitable drive remotely controlled from above ground level for example. The hose 36 and/or the submersible pump 34 may alternatively be directly connected to the chain 16 in a manner permitting rectilinear and possibly lateral movement thereto. In a preferred arrangement (Fig. 4), the sledge 18 is fitted at each side with one or more laterally-extending drag trawls or plates 40 vertically hinged or pivoted to a respective runner 20, each drag trawl or plate 40 being also connected to the runner 20 by a chain 41 or similar. If more than one drag trawl or plate 40 is secured to a runner 20 then they are, as shown, longitudinally spaced along the runner 20. In the forward movement of the sledge 18 these lateral trawls or drag plates 40 pivot outwards or spread like wings to collect and move grit towards the submersible pump 34, the chains 41 restricting opening movement of these trawls or drag plates. During rearward movement of the sledge 18 the trawls or drag plates 40 fold forwardly and inwardly towards the runners 20. In a first modification of the sledge 18 (Fig. 5) fixed outrigger bars or strips 42 are secured to the runners 20 to assist in directing grit from the side of the sewer inwardly towards the sledge 18 for collection during a subsequent forward run by the sledge 18. In a second modification of the sledge 18 (Fig. 6), pivotal lateral plough plates 43 are connected to the runners 20 also to direct grit from the sides of sewer 10 towards the sledge 18 for collection during a subsequent forward run by the sledge 18. These pivotal plough plates 43 are not connected to the runners 20 by chains but otherwise have the same pivotal action as the trawls or drag plates 40. A sledge 18 may be fitted with lateral trawls or drag plates 40, or fixed outrigger bars or strips 42, or pivotal plough plates 43, or any combination thereof. A modified sledge 18A is shown in Fig. 7, and parts similar to parts of the sledge 18 are indicated by the same references with the suffix "A". In this sledge arrangement, the lateral or side runners 20A are disposed only towards the rear end 21A of the sledge 18A and the front part of the sledge 18A is provided with a central runner 44 to which are pivoted trawls or drag plates 40A connected to the central runner 44 by chains 41A. The lateral trawls or drag plates 40 or 40A instead of being vertically hinged or pivoted may (see Fig. 8) be replaced by trawls or drag plates 40B pivotal about a horizontal axis 45 so that in rearward movement of the sledge 18B they pivot upwards as indicated by arrow "X". Abutments 46 are provided on lateral runners 20 or central runner 44 or restrict rearward movement of the trawls or drag plates 40B during forward movement of the sledge 18B. Another form of trawling means 13 is shown in Figs. 9 and 10. The trawling means, in this instance, comprises a pair of trawls or drag plates 47 adapted to extend across the diameter of the sewer 10 but capable of being moved into a substantially face-to-face position. For this purpose the trawls or drag plates 47 are geared together as is diagrammatically indicated at 48. The trawls or drag plates 47 are fitted with small ski-like formations 49 top and bottom to prevent engagement with any uneven fabric of the sewer wall. The intergeared trawls or drag plates 47 are supported on a carriage 50, preferably sledge mounted but possibly wheel mounted. The trawling means 13 is reciprocated to and fro along the sewer 10 between the upstream manhole 11 and the downstream manhole 12. This reciprocation may be effected manually by upstream and downstream drag lines connected to the trawling means, or such drag lines may be connected to appropriate winches disposed within the sewer 10 or above ground level for powered reciprocation. In this embodiment, the movement of the trawling means 13 along the chain track 16 between the upstream manhole 11 and the downstream manhole 12 is by means of a reversible air motor 51 driving a chainwheel 52 meshing with the chain 16. Reference is made to Fig. 11 which shows a grit-collection sledge 18C identical with that shown -and described with reference to Figs. 1 to 4 but with a single drive arrangement 25A identical with the drive arrangement 25. However, in this instance the drive arrangement 25A is disposed centrally (longitudinally and laterally) of the deck 19A and the chain 16 is constrained and guided by front and rear guides 53, 54 which may, for example, be in the form of eyebolts. An alternative sledge-reciprocating arrangement is shown in Fig. 12 where there is shown a grit-collecting sledge 18D identical with the sledge of Figs. 1 to 4. In this instance, the chain 16 is anchored to the sledge 18D in any convenient manner to ensure rectilinear to-and- fro movement and the ends of the chain, or alternatively a rope, 16 are secured to winches 55 and 56 which alternately pull (wind-up) the chain or rope 16 to move the sledge 18D in the direction of the respective winch 55 or 56. These winches 55, 56 may be located in the sewer 10 or above ground level or other convenient upper level. It has been mentioned that to ensure satisfactory removal of the collected grit G it may be necessary to move the inlet of the extraction pump system 15 longitudinally and/or laterally. An alternative is shown in Fig. 13 where a grid-like ramp 57 is built at the grid-removal location with a submersible pump 58 disposed thereunder, a removal hose 59 being connected to the pump 58. In this arrangement, the sledge 18E (identical with that of Figs. 1 to 4 for example) at the end of its grit-collection travel (forward movement) is pulled up the ramp 57 which causes grit G to fall below the latter directly into the region occupied by the pump 34 whereat the grit G is fluidised as aforesaid and pumped upwardly via hose 59 out of the sewer 10. The ramp 57 at its lower inclined end may be imperforate to ensure the deposit of grit G close to the pump 58. As regards the extraction pump system 15 it will be manifest that any convenient form of pump may be employed. Also the pump of whatever construction need not be at the bottom end of the system. It may, in fact, be, above ground level with grit entering the system directly through the hose. The pump may, inter alia, be a jet pump, an example of which is a water-driven venturi pump. To assist grit extraction and ensure that it is not washed downstream the sewer 10 may be dammed, for example by sandbagging, a short distance downstream of the extraction pump system location. The separation of grit from water in the hopper or skip 37 may be effected in any convenient way but preferably by grit settlement and a meandering grit-water path may be provided in the hopper or skip 37 to assist such settlement. Where laterally-extending trawls or drag plates are provided on the grit-collection sledge, these may be protected by bowed resilient metal buffers connecting the front and rear regions of the sledge and extending outwardly of the trawls or drag plates. Any lateral impediment, such as a ladder down a manhole or inspection hole, would thus be encountered by the appropriate buffer and not directly struck by the trawl or drag plate which otherwise might be damaged or even broken off. The lateral trawls or drag plates may alternatively be designed to fold backwards if they encounter an overload or severe obstruction. In this instance re-set means such, for example, as air pistons may be provided to restore them to their working dispositions. The trawling means may be symmetrical in design and fitted with "banjo" air connections to permit upside down working.

Claims: CLAIMS 1. Apparatus for removing grit from sewers comprising an extraction pump system adapted to extend from the sewer to above ground level or other upper level for the upward conveyance of grit, and trawling means disposed within the sewer for dragging grit along the sewer to, or adjacent to, an inlet of the extraction pump system. 2. Apparatus as claimed in claim 1 in which the trawling means is moveable to-and-fro along a predetermined path at or adjacent one end of which is disposed the inlet of the extraction pump system. 3. Apparatus as claimed in claim 2, in which the path is rectilinear and in which the trawling means is reciprocated to-and- fro along the path with the extraction pump system at or adjacent one end of the rectilinear path. 4. Apparatus as claimed in claim 3, comprising a track means adapted to be laid along a length of sewer, the track means being drivingly engaged by the trawling means whereby the latter pulls itself to-and-fro along the track means. 5. Apparatus as claimed in claim 4, in which the track means is a chain anchored at opposed ends' and engaged by a driven chainwheel carried by the trawling means. 6. Apparatus as claimed in claim 5, in which the trawling means comprises a deck mounting a reversible air motor which drives the chainwheel. 7. Apparatus as claimed in claim 6 comprising, on the deck, a pair of longitudinally-spaced reversible air motors each driving a chainwheel in mesh with the chain track. 8. Apparatus as claimed in claim 6, in which the reversible air motor and its driven chainwheel is mounted centrally of the deck with, at the front and rear of the deck a fixed guide through which the chain track extends. 9. Apparatus as claimed in any one of claims 5 to 8, in which the or each air motor drives its chainwheel via a reduction gear, there being an idler chainwheel associated with the drive chainwheel to ensure meshing of the chain track with the latter. 10. Apparatus as claimed in claim 3, in which the rectilinear path is defined by a chain connected to the trawling means intermediate its ends which are operatively connected with a pair of winches which are operated to pull the trawling means to-and-fro along the rectilinear path. 11. Apparatus as claimed in any one of claims 6 to 10, in which the trawling means is a sledge comprising a pair of lateral runners secured to and depending from the deck, there being suspended from the deck a downwardly and forwardly inclined trawl or drag plate for engaging and driving grit along with the sledge. 12. Apparatus as claimed in claim 11, in which the sledge is closed at its rear between the runners and is provided with a rearwardly disposed trawl or drag blade and at least one forwardly disposed pivotally mounted trawl or drag blade adapted on backward movement of the sledge to pivot forwardly upwardly towards the underside of the deck. 13. Apparatus as claimed in claim 11 or 12, comprising a trawl or drag plate laterally-extending from each runner and pivoted thereto for forward pivoting movement alongside the runner upon backward movement of the sledge. 14. Apparatus as claimed in claim 13, in which the lateral trawl or drag plate is also flexibly connected to the runner to restrict its open grit-collection disposition. 15. Apparatus as claimed in any one of claims 11 to 14, comprising, extending from each runner, a fixed outrigger bar or strip and/or a pivotal plough, each adapted to direct grit at the side of the sledge into the path of the latter for collection during subsequent forward travel of the sledge. 16. Apparatus as claimed in claim 6, in which the trawling means is a sledge comprising a pair of rearwardly-disposed lateral runners secured to and depending from the deck, and a forwardly, centrally- disposed runner secured to and depending from the deck, there being pivoted to each side of the forward runner a laterally- extending trawl or drag plate adapted for movement between an open grit-collecting position on forward movement of the sledge and a position forwardly alongside the central runner on backward movement of the sledge. 17. Apparatus as claimed in claim 16, in which each lateral trawl or drag plate is also flexibly connected to the central runner to restrict its open grit-collection disposition. 18. Apparatus as claimed in claim 16 or 17 in which the sledge is closed at its rear between the lateral runners which at their forward ends are joined by a forwardly and downwardly inclined trawl or drag plate. 19. Apparatus as claimed in claim 5, in which the trawling means comprises a pair of side-by-side trawls or drag plates pivotal between a first position where they extend across the diameter of the sewer during movement of the trawling means towards the extraction pump system and a second position where they lie substantially face-to-face during movement away from the system. 20. Apparatus as claimed in claim 19, in which the trawls or drag plates are inter-geared so that they automatically take up the respective positions in accordance with the direction of movement of the trawling means. 21. Apparatus as claimed in claim 20, in which the first position is imposed on the trawls or drag plates by the grit volume encountered during travel towards the extraction pump system while the second position is imposed by the action of the water in the sewer. 22. Apparatus as claimed in claim 20, in which positive drive means is connected to the gearing between the trawls or drag plates to move the latter to the appropriate position. 23. Apparatus as claimed in any one of claims 1 to 22, in which the extraction pump system comprises a pump and delivery hose extending between a region at or adjacent an end of the predetermined trawling path and a collection location above ground level or other upper level. 24. Apparatus as claimed in claim 22, in which liquid-delivery or supply means is provided at said region for fluidising or assisting in fluidising the grit for extraction purposes. 25. Apparatus as -claimed in claim 23 or 24 in which the pump is a submersible pump at the lower end of the delivery hose. 26. Apparatus as claimed in claim 23 or 24, in which the pump is a jet pump at the upper end of the delivery hose. 27. Apparatus as claimed in claim 25 or 26, in which the pump or hose end is located below a perforated ramp within the sewer and through which trawled grit falls for collection and removal. *28. Apparatus for removing grit from a sewer, substantially as hereinbefore described with reference to the accompanying drawings. 29. . Trawling means for grit collection as claimed in any one of claims 1 to 28. 3Θ. A sledge for use in trawling grit along a sewer for deposit at or adjacent to an inlet of an extraction pump system, the sledge comprising pivotal centrally and/or laterally disposed trawls or drag plates adapted in one direction of movement of the sledge along the sewer towards the extraction pump system to collect and push grit towards the latter and in a reverse direction of movement to fold against the sledge body to facilitate unimpeded return movement of the sledge. 31. A sledge as claimed in claim 30, comprising reversible drive means adapted for engagement with a fixed track laid along the sewer to move the sledge in a reciprocating manner along the sewer. 32. A sledge for use in trawling grit along a sewer for deposit at or adjacent to an inlet of an extraction pump system, substantially as hereinbefore described with reference to the accompanying drawings. 33. A method of removing grit from a sewer, the method comprising the steps of pumping grit which may be fluidised (liquidised) out of the sewer to a collection location above ground level or at an upper level, and reciprocating trawling means to-and- fro along the sewer to deposit grit in a region from which it can be pumped. 34. A method of removing grit from a sewer, substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: GRACE JOHN COLIN, GRACE, JOHN, COLIN
Applicants: TATE PIPE LINING PROCESSES LIM, TATE PIPE LINING PROCESSES LIMITED
Application year: 1990
Main classification: E03F9
IPC codes: B08B9, E03F9