US3906737A

US3906737A - Sewer laying system

Info

Publication number: US3906737A
Application number: US404847A
Authority: US
Inventors: William R Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-10-09
Filing date: 1973-10-09
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

The sewer laying system comprises a tile setting apparatus which rides along the bottom of a ditchline and lays compacted layers of aggregate material under and over tiled sections, and which provides mechanical force for setting sections of tile into the pipeline.

Description

United States Patent 1191 Brown Sept. 23, 1975 1 SEWER LAYING SYSTEM 2,738,745 3/1956 Harpold 61/72.l 3,290,804 12/1966 6l/72.l X [76] Invent f' Bmwn, BOX 3,421,609 1/1969 Schmunk 193 2 Kmgston, ldahO 83839 3,820,345 6/1974 Brecht 61/72.l x [22] Filed: Oct. 9, 1973 Primary Examiner-Jacob Shapiro [211 App! 404847 Attorney, Agent, or Firm-John W. Kraft; Charles L.

Kraft, II [52] US. Cl. 61/72.5; 61/41 A; 214/1 PA;

214/17; 404/106 57 B TRACT [51] Int. Cl. E02F 5/10 1 A S [58] Field of Search 61/72.1, 72.2, 72.5, 72.7, The Sewer laying System comprlses a settmg pp 61/41 A; 404/106, 101; 214/1 PA, 17, 185 PH ratus which rides along the bottom of a ditchline and lays compacted layers of aggregate material under and 5 References Cited over tiled sections, and which provides mechanical UNITED STATES PATENTS force for setting sections of tile into the pipeline. 2,656,800 10/1953 Reising 61/72.1 18 Claims, 13 Drawing Figures US Patent Sept. 23,1975 Sheet10f6 3,906,737 I US Patent Sept. 23,1975 Sheet 2 of6 3,906,737

US Patent Sept. 23,1975 Sheet 3 of6 3,906,737

US Patent Scpt. 23,1975 Sheet 4 of6 3,906,737

US Patent Sept. 23,1975 Sheet 5 of6 3,06,737

FIG. M)

Era? 2: il-F FIG. 1111 US Patent Sept. 23,1975 Sheet 6 of6 3,906,737

FIG. 13

SEWER LAYING SYSTEM FIELD OF THE INVENTION The present invention relates to apparatus for laying subterranean pipelines, and, more particularly, to apparatus for mechanically laying tile, which may propel itself along a ditchline.

DESCRIPTION OF THE PRIOR ART Laying of tile for subterranean sewers and pipelines and the like may be conveniently divided into a tile setting function, and a tile and aggregate feeding function. The tile setting function entails placing a base layer of aggregate material which supports the tile, feeding and setting the tile into the ditchline, and placing a cover layer of aggregate material over the top to hold and drain the tile. This process has been accomplished by a variety of apparatus having variously configured housings which usually include solid walls of the ditchline, having means for laying aggregate material adjacent the tile, and having various aggregate feeding means, tile hoists, lifts and chutes, and the like. It is typical of the prior art that the apparatus be propelled by lifting or dragging the housing along the ditchline. Further, it is an apparent convention that the housing of the tile laying apparatus be fabricated of rigid walls which necessitate the removal of the entire apparatus from the ditchline when encountering pipelines, telephone and power cables, and similar obstructions, or the temporary disconnection of utility lines. Thus, it may be seen that tile laying apparatus of the prior art required large capacity lifting apparatus to be operable.

A tile laying apparatus of the prior art has provided a multiplicity of aggregate feeding means which merely lay aggregate in place. It is broadly recognized that this loose, uncompacted aggregate laid in a smooth line will necessarily settle in an even repose. It is a further element of the prior art that some back force may be applied to the tile as it is set. High-back force on the en- -tire line is seldom appliedpthus, joints aligned during the initial tile-setting steps may become loosened, or not fully engaged, as the pipeline progresses. Some well received tile laying apparatus of the prior art have attempted to mitigate these problems by laying a base layer of aggregate-like curvature in which the pipe may rest. This solution assumes that the lower apex of the concave arc of the aggregate is in alignment with the ideal centerline of the pipeline; this is seldom true. It should be noted that guidance of pipe laying apparatus characteristically omitted any integrated guidance and alignment indicating meansgalignment has conventially .been accomplished by a simple transom shot over the top of the pipeline housing.

Accordingly, it is an object of the present invention to provide an apparatus for laying subterranean pipelines having a tile setting apparatus and a closely associ- 'ated tile and aggregate feeding apparatus.

It is a further primary object of this invention to provide a self-propelled tile setting apparatus.

It is an object of this invention that the aforesaid tile setting apparatus be provided with means for laying a compacted base layer of aggregate material, and a suitable top layer. I

It is an object of this invention to provide the aforesaid tile setting apparatus with means for applying back force on tile and pipeline.

It is' another object of this invention to provide aforesaid tile setting apparatus with telescoping side walls to permit passage of the apparatus under pipelines, utility cables and the like.

It is an object of the present invention to provide aforesaid tile setting apparatus with an integrated fundamentally accurate guidance and alignment indicating apparatus.

It is an object of this invention to provide the aforesaid tile and feeding apparatus with integrated frame works and prime movers for moving tile and aggregate.

These and other objects shall become apparent from the description following, it being understood that modifications may be made without affecting the teachings of the invention here set out.

SUMMARY OF THE INVENTION The sewer laying system comprises a tile setting apparatus which rides along the bottom of a ditchline and lays compacted layers of aggregate material under and over tiled sections, and which provides mechanical force for setting sections of tile into the pipeline. The tile setting apparatus comprises a chassis trestle, a tilebed laying car which runs on the top rails of the chassis trestle, and a cover car which also rides on the top rails of the chassis trestle behind the tile-bed laying car. The tile setting apparatus may be actuated forwardly along the ditchline by forcing the tile-bed laying car against the ditchline to force the trestle forwardly.

A more thorough and comprehensive understanding may be had from the detailed description of the preferred embodiment when read in connection with the drawings forming a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a right front perspective view of the sewer laying system of this invention including the tile setting apparatus and the tile carrying and service unit.

FIG. 2 is a right side elevational view of the apparatus of FIG. 1.

FIG. 3 is a right front perspective view of the tile setting apparatus.

FIG. 4 is a fragmentary right side elevational view of the lead tile-bed laying car of this invention shown on a trestle broken away for illustrative purposes.

FIG. 5 is a front end elevational view of the lead car taken substantially from the line 55 of the FIG. 4.

FIG. 6 is a perspective view o'fa section of a top rail of the trestle, and of a typical car wheel shown with the car wheel in its respective operating positions in solid and broken lines for illustrativepurposes.

FIG. 7 is a front end elevational view of the backfill car of this invention, shown; in an environment with subsoil, tile, and aggregates.

FIG. 8 is a side elevational view of the apparatus of the FIG. 7, shown with a portion of its side wall broken away for illustrative purposes.

FIG. 9 is a left side elevational view of the tile setting apparatus shown with the cars in the first phase of operation.

FIG. 10 is a left side elevational view of the apparatus in the FIG. 9 shown with its left trestle wall removed and a compact layer of aggregate material laid by the bed laying car, and with a section of tile installed waiting to be covered with aggregate by the backfill car.

FIG. 1 1 is a left side elevational view of the apparatus of the FIG. shown with a layer of compacted backfill laid over the new section of tile.

FIG. 12 is a fragmentary perspective view of the backfill laying car showing the tamper thereof.

FIG. 13 is a schematic diagram of the hydraulic system of the tile setting apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to the FIGS. 1 and 2, the sewer laying system of this invention comprises a tile setting apparatus and a tile carrying and service unit, generally identified by the numerals 10 and 11 respectively. The present sewer laying system is intended to handle tiles 12 and fill material by means of the tile carrying and service unit 11 and to set tiles 12 and backfill aggregate material by means of the tile setting apparatus 10. As shall become more clear hereinafter, the tile setting apparatus 10 and the tile carrying and service unit 1 1 may be used as separate apparatus in their further respective purposes.

As shown in the FIG. 3, the tile setting apparatus 10 comprises a chassis trestle 13, a tile-bed laying car 14, and a cover fill car 15. The trestle 13 comprises a pair of parallelly disposed base rails 16 and 16', a pair of parallelly disposed top rails 17 and 17' disposed parallelly over the base rails 16 and 16' respectively, and a multiplicity of suitable pillars 18 and diagonals 19 supporting the top rails 17 and 17' over the respective base rails 16 and 16'. The

base rails

16 and 16 may be fabricated of rolled section or box girders. The

base rails

16 and 16 provide skids upon which the trestle 13 may rest and move. The top rails 17 and 17', which shall be described at length hereinafter, carry cars 14 and and are fabricated in an interiorly disposed C-shaped configuration against which the

cars

14 and 15 may act. Transverse beams 20 connect the terminal ends of the base rails 16 and 16' and the top rails 17 and 17' respectively. The forwardmost terminal end of the trestle 13 is provided with upwardly curved, boat-like nose 21 which may minimize or eliminate bulldoze effects of the forward motion of the trestle 13 over the ground, hereinafter later described.

The tile-bed laying car 14 is the forward car of the

cars

14 and 15 in the trestle 13. It is intended to apply a layer of compacted aggregate material on which the tiles 12 may rest. Referring to the FIGS. 3, 4, and 5, the tile-bed laying car 14 includes a chute-hopper 22, which is open at the top and bottom, having a pair of substantially

upstanding side walls

23 and 23, and a pair of

end walls

24 and 24 which are inclined away from the transverse centerline of the car 14. The chutehopper 22 is distally narrower than the interior distance between the

top rails

17 and 17 of the trestle 13, and rides on the

top rails

17 and 17 on trolleys 25, as shown more clearly in the FIG. 6. The trolleys 25 are mounted at the forward and rearward ends of the chute-hopper 22, each of which rides within the

top rails

17 and 17. The trolley wheels 25 are provided on transversely disposed shafts 25". The circumferential edge of each of the trolley wheels 25' is provided with centrally disposed gear teeth 26 and rims 27 and 27' at each side of the teeth 26. Thus, it may be seen that the teeth 26 are substantially flush or recessed with respect to the rims 27 and 27'. The top rails 17 and 17' have a substantially upstanding C-shaped configuration with the openings thereof disposed centrally with respect to the rectilinear central line of the trestle 13. The interior sides of the upper and lower walls of the

top rails

17 and 17 are provided with racks 28 and 28' respectively. The vertical distance between the upper and lower racks 28 and 28' is distally greater than the outer diameter of the wheels 25'. The forward trolley shaft 25" is driven by a prime mover, such as a hydraulic motor 29 mounted to the forward side of the car 14. The motor 29 may be mechanically connected to the shaft 25" by a gear box 30 in a manner which becomes more clear hereinafter. In operation, the car 14 may be driven with respect to the

rails

17 and 17 by engaging the wheels 25' with either appropriate rack 28 or 28', and activating the motor 29. It is to be understood that, although a single motor 29 has been described, a pair of motors may be employed on each shaft 25", and the corresponding idling shaft may be provided with smooth wheels.

The bottom of the car 14 is open, and the

end walls

24 and 24 are provided with spreading means distally narrower than the distance between the base rails 16 and 16. The opening of the bottom of the car 14 is operable to release a predetermined flow of aggregate; and, thus, when taken with the usual speed of the car 14 moving with respect to the trestle 13, the car 14 provides a predetermined thickness of compacted aggregate material at the bottom of the ditchline. The'rearward wall 24 is provided with a reciprocating tamper 31. The tamper 31 is substantially coextensive in width with the wall 24', and rides frictionlesslymithin tracks 31 fastened to the vertical edges of the wall 24'. The tamper 31 may be reciprocated with respect to the wall 24 by any of a variety of mechanical means, such as an hydraulic motor 32 connected to the tamper 31 by an eccentric linkage 33. The reciprocating tamper 31 is operable to compact material issuing from the bottom of the chute-hopper 22 as the car 14 progresses with respect to the trestle 13.

The capacity of the chute-hopper 22 may be increased by providing telescoping walls 34. The telescoping walls 34 may comprise a variety of nestling segments 35. Each segment 35 comprises a polygonal enclosure of upstanding metal strips. The upper terminal edge of each segment 35 is provided with lips (not shown) which interlock with each respective segment 35 above and below, with the lowest segment 35 fastened to the uppermost edge of the chute-hopper 22. The walls 34 may be lowered and extended by a hydraulic cylinder 36 which is pivotally mounted between the uppermost terminal end of the hopper-chute 22 and the uppermost terminal end of the telescoping walls 34. In operation, when the car 14 encounters an obstacle which could collide with the telescoping walls 34, the hydraulic cylinder 36 may be permitted to contract to collapse the telescopic walls 34. When the car 14 progresses past the obstacle, the hydraulic cylinder 36 may be extended to extend the walls 34. It may be seen that the walls 34 permit the car 14 or the trestle 13 to be moved through a ditchline having obstacles without necessarily removing the tile setting apparatus 10.

The car 14 includes a tile setting bumper 38 by which compressive force may be applied to the bell flange portion 12' of a tile 12 being installed in a pipeline. The bumper 38 comprises a rearwardly projecting sideframe 39 issuing from the lower and upper rearward terminal side of the chute-hopper 22, at'the rearward end wall 24, and a push-ring 40. The sideframe 39 may include a suitably stressed structure consisting of a lower beam 41 fastened to the lowermost terminal end of the rearward wall 24' of the chute-hopper 22, a but tress of stringers 42 which provide a box-like support structure for the lower beam 41," and crossties 43' and diagonals 44 to provide structural strength. The pushring 40 is an upstandingly disposed member which may be fabricated as a wall to contact the terminal "end of the bell flange 12', or as a member operable to both contact the terminal end and engage the bell flange 12'. In operation, the motor 29 may be used to drive the car 14 in a rearward direction with respect to the trestle 13, and the resultant force thus'provided may be transmitted through the bumper 38 to the tile 12. It may be seen that the force applied by'the bumper 38 would almost necessarily be in alignment with the pipeline, thus providing better engaged tiles 12.

Referring again to the FIG. 3,the rear cover car 15 is operable to cover the tile 12 with a compacted layer of aggregate material. As shown in'FIGS. 7 and 8, the car 15 is fabricated similarly to the car 14. The ca'r 15 includes a chute-hopper 45 including upstanding side walls 46 and 46' and forward and

rearward incline walls

47 and 47; and is open at the uppermost terminal ends in the same fashion as the chute-hopper 22. The car 15 also includes telescoping walls 48 similar to the walls 34, controlled by a hydraulic cylinder 49. The car 15 is also provided with trolleys 52, comprising geared wheels 51 on a transverse shaft 52' driven by a motor 53 in the manner of the trolleys 25 set out above.

As shown more clearly in the FIG. 12, the cover car 15 is also provided with a reciprocating tamper 54. The tamper 54 is actuated in a frictionless track 55 by a prime mover, such as an hydraulic motor 56 mounted to the rearward side of the chute-hopper 45 and connected to the tamper 54 by a pivotally, eccentrically mounted linkage 57. As shown in the FIG. 7, the lowermost terminal edge of the tamper 54 is provided with a centrally disposed curve recess 54' which permits the lower edge of the tamper 54 to follow the intended curvature of the tile 12 covered with aggregate. The lowermost terminal edge of the

end walls

47 and 47 of the chute-hopper 45 is provided with a curved recess to apply a uniform layer over the upper curvature of the compacted, aggregate-covered, tile 12.

Referring again to the FIGS. 3 and 13, each side of the forwardmost end of the trestle 13 is provided with a pair of substantially upstanding cylinders 58 having weight-distributing pads 59 at the lowermost terminal ends of the respective pistons and valve means 58.. The tile-bed laying car 14 is provided distally from each side of the forwardmost end wall 24 with upstanding cylinders 60. Each of the cylinders 60 is provided with weight-distributing pads 60 on the lowermost end of the pistons, and valve means 60". The car 14 having a suitably powerful motor 29 may be used alone to actuate the trestle 13. It may be seen that the car 14 operates through the central balance region of the trestle 13 to carry and distribute the weight of the apparatus during relocation along the ditchline. Each side of the rearward, cover-fill car may be provided with upstanding cylinders 61 having pads 61 at the lowermost terminal ends of the pistons, and control valves 61". The cylinders 61 of the car 15 may provide further weight support. The cylinders 61 may also be projected from the car 15 at a suitable angle to provide means for applying resultant force if the car 15 is used to drive a trestle 13 along the ditchline as shall be described hereinafter.

As shown more clearly in the FIG. 13, any of a number of types of prime movers to be employed in the tile setting apparatus 10 may be selected, including a hydraulic system connected to a common source which shall hereinafter be described. Accordingly, the prime movers may be provided with closed conduit connections singularly or in several combinations, and may be provided with valve means of the type set out above. It may also be seen that equivalent prime movers may include'electric motors and winch and cable rigged connections.

Referring to the FIGS. 9, l0, and 11, the mode of operation of the tile setting apparatus 10 is shown to advantage. As shown in the FIG. 9,

cars

14 and 15 are filled with a suitable aggregate material; and are positioned at the rearwardmost terminal end of the trestle 13. It may be seen that the cover car 15 has covered the pipeline to a point distally from its forwardmost terminal end with a layer of compacted aggregate material. As shown in the FIG. 10, the forward, bed laying car 14 is moved forwardly with respect to the trestle 13, and lays a suitable layer of compacted aggregate material as set out above. Sections of the tile 12 may be laid within the trestle in the pipeline and may be engaged by the means of 'the bumper 38 as set out above. As shown in the FIG. '11, the cover car 15 may then cover the newly added tiles 12 with a layer of compacted aggregate material, as set out above, to a point distally from the new forward terminal end of the pipeline. The operation for moving the trestle 13 forwardly along the ditchline may be accomplished by first extending the hydraulic cylinders and 61 to retain the

cars

14 and 15 in a stationary position. The

motors

29 and 53 may be activated in a reverse direction of rotation engaging the drive trolleys 25 with the upper racks 28 of the top rails 17 and l7 to drive the trestle 13 forwardly with respect to the

cars

14 and 15 in alignment with the pipeline, as indicated by the arrow in the FIG. 11. The

cars

14 and 15 are then found at the rearward portion of the trestle 13, and may be filled with aggregate materials to repeat the tile laying process. The hydraulic cylinders 58 may be used to partially raise the trestle 13 to reduce friction between the

bottom rails

16 and 16 and the bottom of. the ditchline.

It may be seen that course corrections of the trestle 13 for both direction and grade may be effected by selective activation of the

cylinders

58, 60 and/or 61. Changes in direction may be made by extending one or more of the

cylinders

58, 60 or 61 on one rectilinear side of the trestle 13 more than

cylinders

58, 60 or 61 on the side opposite. In practice it has been found to advantage to control the forwardmost cylinders 58 by separate valves (not shown), thereby controlling the nose 21 with respect to the remainder of the trestle 13. Changes in grade may be made by extending the transversely paired

cylinders

58, 60 and 61 to change the depth of aggregate material laid with respect to the bottom of the ditchline. Again, it may be seen that the forwardmost pair of cylinders 58 may provide the most sensitive and responsive guide means.

Any of a number of means may be used to guide and control the alignment of the trestle 13 on a pipeline course. One suggested means is to direct a surface beam of light, such as a laser beam, through the interior of the pipeline from the rearward end of the pipeline with respect to the trestle 13 to a detector device (not shown) at the push-ring 40 of the bumper 38. One detector means may be to use a photoelectric detector mounted in the push-ring 40. The detector may be connected to servomechanisms for controlling the

hydraulic cylinders

58, 60 and 61; or be connected to indicator means to which the

cylinders

58, 60 and 61 may be controlled manually.

Having thus described in detail a preferred apparatus which embodies the concepts and principles of the invention and which accomplishes the various objects, purposes and aims thereof, it is to be appreciated and will be apparent to those skilled in the art that many physical changes could be made in the apparatus without altering the inventive concepts and principles embodied therein. Hence, it is intended that the scope of the invention be limited only to the extend indicated in the appended claims.

I claim:

1. A tile setting apparatus, comprising:

a chassis trestle including a pair of parallelly disposed base rails, a pair of top rails disposed on pillars parallelly above and in substantial alignment with said base rails, and transverse beams connecting respective terminal ends of said base and top rails;

a tile-bed laying car mounted between said top rails of said trestle on trolleys, one of said trolleys being provided with means for motivating said car along said top rail, said car having side walls and end walls forming an enclosure which is open at the top and bottom to collect and pass a predetermined layer of aggregate material and a tile setting bumper projecting rearwardly from said car and having a push ring having means for engaging a bell flange of a tile; and

a cover fill car being mounted rearwardly of said bed laying car within said trestle on said trolleys, one of said trolleys having means for motivating said cover car along said top rails, said cover car having side walls and end walls forming an enclosure which is open at its top and bottom to collect and release a predetermined layer of cover material over installed tiles.

2. The apparatus of claim 1 wherein said top rails have an upstanding C-shaped configuration with their openings disposed centrally with respect to said trestle, and wherein said trolleys include wheels which may ride within said top rails.

3. The apparatus of claim 2 wherein the interior side of the upper portion of said C-shaped top rails includes a rack, and wherein said trolley wheels include gear teeth which mesh with said rack.

4. The apparatus of claim 2 wherein the interior side of the lower portion of said C-shaped top rails includes a rack, and wherein said trolley wheels include gear teeth which mesh with said rack.

5. The apparatus of claim 3 wherein the circumference of said trolley wheels includes rims disposed at each side of said gear teeth to make flush or recess said gear teeth.

' 6. The apparatus of claim 2 wherein the interiormost vertical distance of said upstanding, C-shaped, top rails is distally greater than the diameter of said trolley wheels.

7. The apparatus of claim 1 wherein each side of said tile-bed laying car includes a pressure cylinder having a piston which is extensible into the bottom of a ditchline to raise said car with respect to said top rail, said cylinders being controlled by suitable valve means.

8. The apparatus of claim 1 including a pressure cylinder mounted at each side distally from the forwardmost terminal end of said trestle, said cylinders being controlled by suitable valve means.

9. The apparatus of claim 1 wherein each side of said cover fill car is provided with a pressure cylinder having a piston which may extend into the ground and raise said car with respect to said top rail, said cylinders being controlled by suitable valve means.

10. The apparatus of claim 1 wherein the uppermost terminal edge of said side walls of said bed laying car is provided with extensible telescoping walls.

11. The apparatus of claim 10 wherein said telescoping walls are extended by a pressure cylinder fastened between the uppermost telescoping wall section and said side wall portion of said bed laying car.

12. The apparatus of claim 1 wherein the uppermost terminal edge of said side walls of said cover car is pro vided with telescoping walls.

13. The apparatus of claim 12 wherein said telescoping walls are extended by a pressure cylinder fastened between the uppermost telescoping wall sections and said side wall portion of cover car.

14. The apparatus of claim 1 wherein the rearwardmost terminal side of said bed laying car is provided with a reciprocating tamper.

15. The apparatus of claim 14 wherein said tamper rides in frictionless tracks and is reciprocated by a motor connected to said tamper by an eccentric linkage.

16. The apparatus of claim 1 wherein said rearwardmost terminal side of said cover fill car is provided with a reciprocating tamper.

17. The apparatus of claim 16 wherein said tamper rides in frictionless tracts and is reciprocated by a motor connected to said tamper by an eccentric linkage, the lowermost terminal edge of said tamper is provided with a centrally disposed recess which follows a predetermined curvature of compacted aggregate material over said tile.

18. The apparatus of claim 1 including an upwardly curved, boat-like nose issuing forwardly from the forwardmost terminal end of said trestle.

Claims

1. A tile setting apparatus, comprising: a chassis trestle including a pair of parallelly disposed base rails, a pair of top rails disposed on pillars parallelly above and in substantial alignment with said base rails, and transverse beams connecting respective terminal ends of said base and top rails; a tile-bed laying car mounted between said top rails of said trestle on trolleys, one of said trolleys being provided with means for motivating said car along said top rail, said car having side walls and end walls forming an enclosure which is open at the top and bottom to collect and pass a predetermined layer of aggregate material and a tile setting bumper projecting rearwardly from said car and having a push ring having means for engaging a bell flange of a tile; and a cover fill car being mounted rearwardly of said bed laying car within said trestle on said trolleys, one of said trolleys having means for motivating said cover car along said top rails, said cover car having side walls and end walls forming an enclosure which is open at its top and bottom to collect and release a predetermined layer of cover material over installed tiles.

6. The apparatus of claim 2 wherein the interiormost vertical distance of said upstanding, C-shaped, top rails is distally greater than the diameter of said trolley wheels.

12. The apparatus of claim 1 wherein the uppermost terminal edge of said side walls of said cover car is provided with telescoping walls.