GB2126683A - Duct motor - Google Patents

Abstract

A duct motor for use in drawing a rope through a duct is driven by air and includes a hollow tubular valve rod 43 made of a flexible plastics material through which air is fed to a gripper bag which is associated with one of a pair of telescopic members. Also described are a spool valve controlling the flow of the air and having a raised portion with square shoulders on its outer surface for co- operation with ball catches, a floating seal allowing lateral pressure on a bag to be taken up, a relief spring arranged to act as a part of a safety valve, an "O" ring seal positioned to enable deflation to occur more rapidly and a bag made from a plurality of pieces of material joined together. <IMAGE>

Description

SPECIFICATION Duct motor This invention relates to apparatus which is capable of being propelled along a cable duct in order to draw a rope or wire along the duct behind it for use in subsequently pulling, for example, a power or telephone cable through the duct.

Apparatus for this purpose, which is often referred to as a duct motor, is known and examples of previously proposed apparatus are described in the specification of U.K. Patent No.

1,044,201 and of U.K. Patent Application No.

8026892.

The present invention has a number of features, each of which enables an improvement to be obtained in the operation of the present apparatus over previously known apparatus.

The present apparatus uses the well known basic mode of operation described in the above mentioned prior patent specifications employing two inflatable devices, generally known as "bags" one on each of a pair of telescopic members, in which the bags are alternately inflated and deflated within a duct and the telescopic members are alternately extended and telescoped together so that the apparatus moves along the duct.

One feature of the present invention involves the use of a comparatively flexible centre tube or valve rod.

A second feature of the present invention is concerned with the construction and operation of a main spool valve.

A third feature of the invention is concerned with the construction of the bags.

A fourth feature of the invention is concerned with the construction and operation of a valve mechanism used in controlling the inflation and deflation of the bags.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figs. 1-3 are longitudinal sections through an apparatus in accordance with the invention; and Fig. 4 is a perspective view of a bag construction.

Referring to Figs. 1-3, which are engineering drawings of a duct motor bearing reference numerals related to a parts list set out at the end of this specification, the following description will be made with reference to the numbers employed to identify the parts in the parts list. It will be appreciated that for the purposes of illustration, the motor is divided into the three parts shown in Figs. 1-3, which it will be understood are, in fact, joined together, end-to-end in practice.

It will also be appreciated that, because the parts are identified by the reference numbers used in the parts list, a single reference numeral is, in certain instances, used to identify more than one similar part, which is used in different parts of the assembly. Thus the two similar bags are identified by the reference numeral 22. However, no confusion results from this procedure in the following description, because the parts are described with reference to specific assemblies.

Furthermore, in order to provide an illustration of the operation of the apparatus with the minimum number of representations, the various parts of the drawing illustrate the parts of the assembly in different operating positions.

The part shown in Fig. 1 illustrates the front part of the motor with a nose 25 and one of the bags 22. An intermediate part of the motor assembly, which includes a piston tube 41, is shown in Fig. 2. The forward end of the piston tube 41, which is closed by a piston tube front cap 44, is shown dotted in Fig. 1 in the position that it occupies when the parts have been telescoped together and a piston rod 42 is largely within the piston tube 41.

In Fig. 2, the piston rod 42 is shown in an intermediate position extending from the piston tube 41 and an end bush 2 of the front part of the motor, which is shown dotted, is at a distance from the piston tube front cap 44.

The rear portion of the motor assembly is shown in Fig. 3 with a rear end coupling plug 79 for coupling air to the assembly and an eye 50 for use in tying a draw wire or rope on to the assembly, whereby the wire or rope may be drawn through a duct along which the motor passes.

Extending forwards from the rear portion of the motor assembly and into the intermediate part of the assembly is a tubular valve rod 43 which constitutes a centre tube of the assembly. The rod 43, which, in one embodiment, has an outer diameter of 0.25 inches (6.35 mm) and a hole diameter of 0.15 inches (3.81 mm) is made of nylon. The use of a flexible plastics tubular rod 43, together with a flexible joint provided by a piston tube rear cap 31, a coupling member 27 having a curved outer end surface which cooperates with a curved inner surface of the cap 31 and a sleeve 30 of a resilient material, for example rubber, held in place by a union nut 28, enables the motor to negotiate bends of smaller radii than would otherwise be possible.

The use of the flexible tubular rod 43, together with the flexible joint, in addition to providing a considerable improvement in the ability of the motor to negotiate bends of small radii, also results in a reduction in the lateral pressure that is exerted on the mechanisms used to operate the bags compared with the lateral pressure that is experienced when a rigid centre tube, for example of stainless steel, is used and the motor is passing around a bend.

The use of a flexible nylon tube allows the improvements of a flexible joint to be included in arrangements in which air for operating the mechanism passes down a centre tube.

The arrangement described above enables considerable flexibility to be given to the rear part of the motor assembly. In order to improve the flexibility of the front part of the motor assembly, a flexible nylon tube 42 has been employed, in one embodiment, in place of a stainless steel tube 42 which has previously been dived for the tube forming the piston rod of the assembly. Duct motors having the improvements described above are able to negotiate bends with radii of 2 or 3 metres, whereas earlier duct motors employing a rigid valve rod and a rigid piston rod previously considered to be necessary have been unable to negotiate bends having such small radii.

Referring to the rear portion of the motor assembly shown in Fig. 3, there is shown a valve assembly including a spool 57 that constitutes the main distribution for compressed air supplied to the motor via plug 79. The function of this main distribution valve is similar to that of valve 7 described in the specification of Patent Application No. 8026892 referred to above and since this function is well known to those concerned with this type of apparatus, it will not be described in detail here.

In its operation, the valve 7 of Patent Application No. 8026892 employs a valve member having grooves in which balls 43 and 44 engage, as shown in Fig. 1 of that specification.

The grooves have angled shoulders and are separated by a flat portion of the valve. There is a tendency, with this arrangement, when the motor is operating slowly, for the balls 43 and 44 to move slowly up the angled shoulders of the valve grooves and the valve spring 1 8 to be depressed slowly, the valve being so moved that the balls reach the narrow flat portion forming a crest between the grooves, the air supply is cut-off and the arrangement becomes stuck in the middle position.

In the arrangement shown in Fig. 3 of the present application, the spool valve 57 has a raised comparatively wide portion with substantially square shoulders mid-way along its length. Ball catches 72, 73, 74 are able to bear against the shoulders of this raised portion and the valve 57 is held firmly in positions by the ball catches 72, 73, 74 bearing against the square shoulders. During one operation of the arrangement, the piston valve spring 39 depresses down until the cap head screw 47 on the valve rod 43 reaches the front spring stop 48 and then the full power of the piston 35 overcomes the ball catches 72, 73, 74 and the spring 39 "flicks" the valve 57 over to its other position.The valve 57 therefore cannot stick in the middle of its travel and the motor will not stop in a duct, but will always try to keep going.

The bag valve mechanism, which is shown most clearly in Fig. 1, will now be described. This bag valve mechanism operates, in principle, in a similar way to the valves 10 and 11 shown in Fig. 3 of the specification of Patent Application No. 8026892, and its detailed operation will therefore not be described in this specification, the general principle of operation being familiar from the earlier patent specification to those skilled in the art. In order to reduce the possibility of the bag valve mechanism jamming when lateral pressure is applied to it, resulting in the motor stopping, or in the bag becoming over-inflated and bursting when the bag comes out of a duct, the following features are incorporated in the present arrangement.

Firstly, an "0" ring seal 11 is located in a carrier 10 forming a collar. The collar is a separate part which can float against a shoulder on the bag pressure valve 14, thereby allowing lateral pressure on the bag tube 3 and 4 to be taken up without affecting the other seals.

Secondly, a relief spring 8 is arranged between the carrier 10 and a spring retainer 9 as a part of a safety valve. Any high air pressure in the bag, that would result in the over-inflation of the bag, is released by the depression of the spring 8, the movement of which allows air to be released past the "0" ring carrier 10.

Thirdly, deflation of the bag is enabled to take place more rapidly than would otherwise be the case, as a result of the fact that when the bag is forced back, as the motor moves forward, air is able to escape past the "0" ring carrier "10".

Furthermore, the assembly of the bag tube 4 and of the "0" ring 1 5 in the bag tube centre bearing 1 9 is such that, during this operation, the "0" ring seal 1 5 is in a position such that air is also able to escape past the seal 1 5 on the bag tube bearing, whereby the rate of deflation is further increased and the motor enabled to operate more quickly.

Referring now to Fig. 2, there is shown a perspective view of a bag 85. The bag 85 consists of four similarly shaped pieces 86-89 of polyurethane sheet, which have straight side edges 90 to end portions and main side edges 91 which are curved.

The side edges 90 and 91 of the pieces 86, 87; 87, 88; 88, 89 and 89, 86 are seam welded together to form the bag 85 which has openings 92 at each end. The pairs of tubes 3, 4 and 69, 70 shown in Figs. 1-3 can be passed through openings 92 in respective ones of the bags 85, which can be clamped to the pairs of tubes by clips 21 in the way shown in Fig. 1.

It will be appreciated that, by joining together an appropriate number of pieces, such as the pieces 86-89, a bag of any desired diameter may be manufactured. It is thus possible to make a bag which can operate in, for example, a 1 2 inch (30 cm) inner diameter pipe or duct comparatively easily.

In making a bag by this method, it is possible to shape the sides of the end portions of each piece, for example by appropriate tapering, so that the resulting openings 92 will fit on to standard pairs of grip tubes, 3, 4 and 69, 70. Alternatively, the openings 92 may be of a larger inner diameter than the outer diameter of the grip tubes and either flanges, upon which the bags may be clamped, may be provided on the grip tubes, or collars may be introduced between the grip tubes and the end portions of the bags.

In one embodiment, a bag, which is capable of being inflated to operate in a 12 inch inner diameter pipe, has openings 92 of 9 inches in diameter, and a collar is introduced between the grip tubes and the bag in order to clamp the bag to the tubes.

Previously, the bags 22 have been made from moulded plastics material and, not only are the tools which are necessary for making the bags expensive to manufacture, but they are oniy suitable for making bags for use in ducts of one particular diameter.

The bags 85 are not only cheaper to manufacture than the existing bags, but the method of manufacture described has the advantage that bags, each capable of being operated in a duct or a pipe having a diameter within a wide range of values, can easily be made.

The pieces 86-89 are seam welded together, in the embodiment described, by heat welding the material along a region close to the edges of pieces which are arranged side by side. Of course, other forms of seam and other shapes of the pieces may be used.

Thus, an outwardly curved edge of one piece may be arranged to overlap a similar but inwardly curved opposite edge of an adjacent piece, the overlapping edges being sealed together.

The edges may be sealed together by any suitable means, for example radio frequency heat welding.

Bag 85, made from 1 2 mil thickness polyurethane sheet material, have proved to be very resistant to abrasion. However, the bags may be made from other materials and with other wall thicknesses.

The comparative ease with which it is possible to produce grip bags which are made from a plurality of pieces and which are suitable for use with duct motors, increases the possibility of using duct motors in ducts and pipes having a diameter within a wide range and enables duct motors to be employed more easily in applications other than pulling-in lines and cables.

For example, by making a wide range of grip bags available more easily and cheaply, the possibility of using duct motors in the pulling of inspection equipment along pipes and ducts of different diameters is increased.

The numbered parts list referred to at the beginning of the specification is now set out below: Part No. Description 1 '0' ring 2 Front grip end bush 3 Front grip tube-back 4 Front grip tube-front 5 Front spring retainer 6 Bag valve spring 7 Circlip 8 Relief spring 9 Spring retainer 10 Bag pressure valve collar 11 '0' ring 12 '0' ring 13 '0' ring 14 Bag pressure valve 15 '0' ring 16 Grub screw Part No.Description 1 7 '0' ring 1 8 Front grip centre tube 19 Air release valve 20 Nylon insert 21 Air bag clip 22 Air bag 23 Nose cap 24 Nose seat 25 Nose 26 C'skscrew 27 Rigid coupling 28 Union nut 29 Washer 30 Sleeve 31 Piston tube rear cap 32 '0' ring 33 '0' ring 34 Piston seal 35 Piston 36 Grub screw 37 Piston stop washer 38 Rear spring stop 39 Piston valve spring 40 Rear spring stop 41 Piston tube 42 Piston rod 43 Valve rod 44 Piston tube front cap 45 Internal distributor seal 46 Scraper seal 47 Cap head screw 48 Front spring stop 49 Spring stop 50 Rope eye 51 Filter 52 Rear valve cap 53 '0' ring 54 Rear valve stop 55 Valve spindle 56 Collar 57 Valve 58 Valve rod coupling 59 '0' ring 60 Valve block 61 Front valve cap 62 C'sk screw 63 '0' ring 64 '0' ring 65 Front valve stop 66 '0' ring 67 '0' ring 68 Rear spring retainer 69 Rear tube grip-back 70 Rear tube grip-front 71 '0' ring 72 Catch screws 73 Catch spring 74 Steel ball 75 Grub screw 76 Air release valve 77 '0' ring 78 Rear grip center tube 79 Instant air female plug 3/8 bsp.

Claims (14)

1. A duct motor including a pair of inflatable gripper bags, a pair of telescopic members, each of the telescopic members being associated with a respective one of the gripper bags for movement therewith and a telescopic member including respectively a hollow piston rod and a piston tube within which the piston rod acts, and a hollow tubular valve rod extending into the hollow piston rod for use in feeding air to operate the motor, the hollow tubular valve rod being made of a flexible plastics material.

2. A duct motor as claimed in Claim 1 including in an end of the piston tube a cap through which the hollow tubular valve rod passes, the cap having a curved end surface, and a coupling member arranged on the tubular valve rod, the coupling member having a curved end surface which co-operates with the curved end surface of the cap to facilitate relative rotational movement of the cap and the coupling member on the valve rod.

3. A duct motor as claimed in Claim 1 or Claim 2 in which the hollow tubular piston rod is made of a flexible plastics material.

4. A duct motor as claimed in any one of the preceding claims in which the flexible plastics material is nylon.

5. A duct motor including a pair of inflatable gripper bags, a pair of telescopic members, each of the telescopic members being associated with a respective one of the gripper bags for movement therewith and a telescopic member including respectively a hollow piston rod and a piston tube within which the piston rod acts, and a hollow tubular valve rod extending into the hollow piston rod for use in feeding air to operate the motor, the valve rod being coupled to a spool valve controlling the air flow, the spool valve having a raised portion with square shoulders on its outer surface, ball catches co-operating with the raised portion during the operation of the motor and a piston valve spring arranged to move the spool valve from one position to another.

6. A duct motor including a pair of inflatable gripper bags, a pair of telescopic members, each of the telescopic members being associated with a respective one of the gripper bags for movement therewith and a telescopic member including respectively a hollow piston rod and a piston tube within which the piston rod acts, a hollow tubular valve rod extending into the hollow piston rod for use in feeding air to operate the motor, a bag tube to which a bag is attached, a bag pressure valve and an "0" ring seal located in a carrier arranged on the bag pressure valve thereby allowing lateral pressure on the bag tube to be taken up.

7. A duct motor as claimed in Claim 6 including a shoulder on the bag pressure valve against which the carrier can float.

8. A duct motor as claimed in either claim 6 or claim 7 including a relief spring arranged between the carrier and a spring retainer to act as a part of a safety valve.

9. A duct motor as claimed in any one of claims 6 to 8 including an "0" ring seal arranged between a centre bearing for the bag tube and the bag tube such that during the deflation of the bag the "0" ring seal is in a position such that air is also able to escape past the "0" ring seal.

10. A bag for use with a duct motor, the bag comprising a plurality of pieces of material, each piece being joined to an adjacent piece at or near each of two opposite edges, a portion at each opposite end of each piece being left free to provide a bag having openings at each end.

11. A bag as claimed in claim 10 in which the pieces are joined together by seam welding.

12. A bag as claimed in either claim 10 or claim 11 in which each of the pieces is of the same shape.

13. A bag as claimed in any one of claims 10-12 in which the pieces are made of polyurethane sheet material.

14. A duct motor as claimed in either claim 1, claim 5, or claim 6 substantially as described herein with reference to Figs. 1-3 of the accompanying drawings.

1 5. A bag for a duct motor substantially as described herein with reference to Fig. 4 of the accompanying drawings.