GPO Vehicles


Make Karrier
Model Gamecock
Type  
Body Builder  
Use Rodding and Light Cabling Vehicle
Registration Number ALT 505H
Fleet Number 203063
Date of picture 1970

Karrier Gamecock Rodding and light Cabling vehicle. This Karrier model used the standard Commer VC cab and this particular vehicle was one of the prototype batch of vehicles for dedicated rodding and cabling work.

 


Rodding and Light-Cabling Vehicle
R. W. MARTIN
An Extract from the P.O.E.E.J Vol 64, page 22 (April 1971)

The Rodding and Light-Cabling Vehicle has been designed to enable a two-man crew to undertake rodding and the installation in duct of cables up to 45 mm diameter. It is anticipated that the crews of these vehicles will do nearly all the rodding and approximately 70 per cent of the light-cabling work of an average Telephone Area. The first vehicle of this class was introduced in February 1969. Since then, six more have been on field trial, and during 1971, 266 vehicles will be provided for use nationally.

FIG. 1 Two-ton AIRVAN

INTRODUCTION
To date, specialist rodding parties have been equipped with 1.5-ton or 2-ton vehicles modified to carry the tools, stores and mechanical aids necessary to carry out rodding operations. In this context, rodding may be defined as the installation in a duct of a drawline which is used to draw in a light cable or a heavier cabling rope.

General rodding practice requires the use of one or more of the following main mechanical aids:

  1. an air compressor which is used typically for operating a ductmotor,

  2. a mangle-type machine for pushing continuous steel rods and which also incorporates a small winch,

  3. an electric generator having an output of 2 kW at 110 volts which is used to power electric road-breaking tools, and

  4. a portable self-priming centrifugal pump-set for removing water from jointing chambers.

These machines are all self-contained and self-powered units which must be removed from the vehicle and set up near the jointing chamber before use. Thus, a considerable amount of time can be spent in off-loading, setting up, dismantling and reloading equipment.

EARLY DEVELOPMENT
A general examination of the problems involved in rodding duct showed that:

  1. for much of the work, a cable could be pulled in as easily as a drawline.

  2. higher efficiency could be achieved by using a vehicle specially equipped to do both rodding and light cabling,

  3. mechanical aids should be built into, and work from, the vehicle to minimize or eliminate off-loading and reloading of heavy plant,

  4. the vehicle should be equipped with suitable guiding devices to enable it to work from the roadside, and

  5. mechanical aids should operate from a common power source, which could be the vehicle engine, but a method of power distribution would be required.

At the time, a commercially-produced vehicle known as the AIRVAN (Fig. 1) came to the notice of the Post Office. The AIRVAN was a 2-ton payload vehicle fitted with an air compressor driven by the vehicle engine. The vehicle had several attractive features, namely that the compressed-air output of the compressor was a readily distributed means of power transmission and the compressor was mounted mainly below the vehicle floor so as not to intrude excessively into the body space.

One AIRVAN was purchased and equipped with a 1,000 lbf line-pull capstan winch, ductmotors, a 2-inch water pump
driven by an air motor and a pneumatically-operated rod pushing machine modified to use 15/16-inch diameter semi rigid polyviny-chloride (p.v.c.) tube instead of the usual steel rod. The winch was mounted in the vehicle and served by fixed piping. The other devices still required to be unloaded for use and were driven by air from the compressor via a live-centre hose reel containing 30 ft of hose. At a later date, the modified pneumatic rodding machine was superseded by the prototype of a new type of rod-pushing machine (Fig. 2) which was fixed in the vehicle and connected to the compressed-air supply by permanent piping. The rod from the reel passed through the machine and was guided from the vehicle to the duct by a flexible tubular guide. This rod-pushing machine could propel the rod backwards or forwards at a maximum speed of 130 ft/mm with a maximum force of 900 lb. Thus, after the rod has been pushed through a duct, cable can be attached and drawn in as the rod is retracted.

FIG. 2 Rod-pushing machine
FIG. 3—Compressor installation on pneumatic Rodding and Light-Cabling vehicles

INITIAL FIELD TRIAL
The field trial of the AIRVAN showed that the basic concept of in-built mechanical aids driven from a single power source could offer distinct advantages. It also demonstrated two major disadvantages of the particular installation, namely, lack of storage space due to the small vehicle size and limited power available for driving mechanical aids due to the poor efficiency of compressed air as a power-transmission medium.

Lack of space could easily be overcome by using a larger vehicle and it was decided to continue and extend the trial using a 5-ton payload chassis powered by a six-cylinder diesel engine, fitted with a three-man cab and a box body. Six chassis were purchased. One was reserved for future alternative development and the other five fitted with air compressors driven by the vehicle engine. The compressor installation used on the 2-ton AIRVAN was readily adapted to the larger chassis and mounted wholly below the vehicle floor (Fig. 3). In addition, equipment similar to that fitted on the earlier vehicle was provided. Thus, the minimum of additional development time was required to equip the five vehicles and the trial was able to continue with the least possible delay.

Compressor Installation
The compressor used on all vehicles was a single-stage oil-cooled rotary type driven at 2,300 rev/mm and rated to deliver 100 ft3 of air free air delivered (FAD) at a pressure of 100 lbf/in2. It was driven by the vehicle engine via a drive-line power take-off with a 1/1 transfer gear ratio. This ratio was later changed to 1/1 33 to enable the engine speed to be reduced to about 1,750 rev/mm to diminish noise levels. Engagement of the power take-off automatically increased engine revolutions to the speed required to drive the compressor. This was effected by a solenoid connected to the engine throttle linkage and energized by the operation of a micro-switch when the power take-off engaged.

Secondary control of engine speed was effected by a bellows mechanism inserted in the engine throttle control linkage and operated by air pressure feed back from a suction unloader assembly on the compressor. This mechanism operated to reduce engine speed to approximately 1,000 rev/mm when pressure in the air receiver rose to 100 lbf/in2 and automatically increased engine revolutions to normal working speed when pressure in the air receiver fell.

Alternative Power Transmission System
To overcome the major disadvantage of poor efficiency of the compressed-air system, possible alternative systems were investigated and the obvious choice seemed to be an oil hydraulic system. Such a system offered a number of advantages including:

  1. high efficiency, which for individual hydraulic components can be better than 90 per cent and with reasonably careful design, a system efficiency of 60-70 per cent can be achieved,

  2. easy power distribution as pipes could be run to any part of the vehicle,

  3. a wide choice of hydraulic equipment is readily available,

  4. hydraulic pumps and motors are compact units with a high power-to-weight ratio, and

  5. hydraulic systems, when properly set up and commissioned, are generally reliable in operation.

A decision was, therefore, made to proceed with the design of a Rodding and Light-Cabling vehicle on which all the inbuilt mechanical aids would be hydraulically driven.

An experimental hydraulic system was designed and fitted to a standard British Post Office 4-ton vehicle. Full advantage was taken of the increased power available from the hydraulic system to equip the vehicle with all necessary mechanical aids which could be built into, and operate from, it. When complete, the vehicle was subjected to a short intensive field trial for the purpose of gaining operational experience with the hydraulic system and assessing the usefulness of the mechanical aids fitted.

PROTOTYPE HYDRAULIC RODDING AND LIGHT CABLING VEHICLE

From experience with the experimental vehicle it was decided that a prototype should be equipped with:

  1. a low-pressure (100 lbf/in2) air compressor to operate a road breaker and other pneumatic tools,

  2. a high-pressure (200 lbf/in2) air compressor to operate ductmotors,

  3. a hydraulically-powered version of the new rod-pushing machine,

  4. a 2 kW, 110-volt, 50 Hz electric alternator,

  5. a 2,000 lbf line pull variable-speed capstan winch, with power-driven rope take-up reel, and

  6. a 3-inch self-priming centrifugal pump.

Each appliance had its own motor and the hydraulic system was designed to allow any one item to be powered by an hydraulic pump driven via a power take-off fitted to the offside of the vehicle gear box. Maximum system pressure was 2,000 lbf/in2.

A pump rated to deliver 10.5 gal/mm at a vehicle engine speed of 1,000 rev/mm was chosen. This output closely matches the requirements of items (c) and (e). Items (b), (d) and (f) each require less than l0.5 gal/mm so the flow was restricted by a pressure-compensated flow-control valve in series with each of these appliances. The low-pressure compressor, required a flow of 15 gal/mm and this was provided by increasing the vehicle engine speed to approximately 1,400 rev/mm while the compressor was in use.

The system of automatic selection of engine speed when the power take-off is engaged was adapted to the hydraulic vehicle and extended so that, when the low-pressure compressor control valve was operated, a second solenoid increased the engine speed to 1,400 rev/mm.

FIG. 4 Prototype hydraulic vehicle showing left-hand racking and winch with rope arranged

Control valves were mounted at operationally convenient points and, where possible, so that they could be operated without entering the vehicle. To guard against more than one appliance being operated at any one time, open-centre valves were used and connected in series so that with all valves in neutral, the full pump output passed through each one in turn and then to the reservoir. When a valve was operated, the pump output was directed to the appliance controlled by that valve and if two appliances were selected, only the one nearest in the circuit to the pump would operate.

The winch consisted of a capstan unit mounted externally below floor level at the rear of the vehicle (Fig. 4) and a rope take-up reel drive unit fitted inside the vehicle. Each part was driven by a separate motor but the motors were connected in series and controlled by a single valve. Rope sheaves were provided to guide the rope from the capstan to the take-up reel and to regulate the layering of the rope on the reel.

Instruments were provided to indicate system pressure, output pressure of the two air compressors, alternator output voltage and system pressure at the winch capstan motor. The latter gauge was calibrated to indicate line pull in pounds force at the winch capstan. A tachometer fitted in the vehicle cab, and driven from the engine camshaft by a flexible shaft, provided a visual indication of engine speed.

TESTING
When the prototype was complete, the unit was subjected to intensive testing designed to assess the reliability of the system and the particular installation. No attempt was made to establish the probable service life of particular components or mechanical aids which were proprietary items operating within the manufacturer’s recommended limits. A separate life test had already been undertaken on the new rod-pushing machine.

FIG. 5 Prototype hydraulic vehicle, general 3/4 rear view of whole vehicle

The test consisted of running the vehicle continuously for a period of 12 hours on five consecutive days. During the test period, one mechanical aid was always in operation, each one in turn being driven for a period of two hours either at maximum rated output or with repeated change from full load to no-load condition. For example, when operating the low-pressure compressor, a simulated road-breaker rig was used to give alternately a 30-second full-load condition followed by 20 seconds at no load. Operating pressures, temperature and speed were continuously monitored at critical points. Noise levels were measured and readings of 61 dB were obtained in the working area immediately behind the vehicle. This is comfortably within the Burns & Littler Damage Risk Criteria, permits normal speech communication, and compares favourably with levels experienced with the pneumatic vehicles.

During the test period, none of the proprietary equipment developed any fault or failed to produce the rated performance. The vehicle engine temperature did not rise above the normal working condition, the temperature of the hydraulic oil remained comfortably within permitted limits and no faults developed on the hydraulic system. Following the period of testing, the vehicle (Fig. 5) entered field service in the Sheffield Telephone Area in January 1970.

FIG. 6 Prototype hydraulic vehicle showing right-hand racking

PLANT AND TOOL STORAGE
All the experimental vehicles, except for the original AIRVAN, are fitted with racking designed to provide accommodation for all the required tools and stores and incorporate some of the mechanical aids.

The racking is made in two parts, fitted on each side within the body of the vehicle, and constructed as individual free-standing units each of which can be fitted to the vehicle as a complete section requiring only to be secured to a few built-in attachment points.

The right-hand (off-side) racking (Fig. 6) incorporates the reel for the 200 yd of p.v.c. duct rod and, on the pneumatic vehicles, the winch. It also provides accommodation for four duct motors and split ducts and incorporates the mounting for the rod-pushing machine. On the hydraulic vehicles, the winch was moved, and the space in the right-hand racking used to accommodate the high-pressure compressor.

The left-hand (near-side) rack (Fig. 4) contains a welfare unit and has accommodation for tools, guards, road signs, sectional duct rods, reels of drawrope and small stores. It also provides writing facilities and storage for such items as drawings, diagrams and works instructions. The vehicle has three external lockers, one for reinstatement materials, one for gas cylinders and one to accommodate a pneumatic road breaker and a pneumatic submersible pump.

FINAL CHOICE
The pneumatic and hydraulic versions of the vehicle perform the same function and works procedures are the same. Thus, the major factors influencing the final choice were the relative efficiency and reliability of the two power systems.
The higher mechanical efficiency of the hydraulic system makes more power available at lower vehicle engine speed. This makes it possible to provide more and higher-powered aids and produces better working conditions.

The compressors on the pneumatic vehicles did not produce their full rated output and, in consequence, the mechanical aids fitted did not operate at full capacity. The compressed-air power available from the compressor was approximately 4 horsepower and was used to the full by the appliances fitted.

The hydraulic system has operated very reliably on trial and with the vehicle engine running at 1,000 rev/mm produces about l4~5 usable horsepower or about 21 horsepower when running at the higher speed. The winch and the rodpushing machine have already been upgraded to produce a higher output than the pneumatic versions and this enables a wider range of work to be undertaken and larger or longer cables to be installed. The hydraulic system, therefore, has the development potential to cater for any new aids which might be introduced during the service life of the vehicles. One development expected to be introduced during the next two years is a redesigned duct motor which will operate from the high-pressure compressor on the hydraulic vehicle but cannot easily be catered for on the pneumatic vehicles.

A hydraulic system was, therefore, chosen as it offered most advantages.

In the field trial, virtually no use was found for the alternator which had been used mainly to operate an electric road breaker. When given a suitable compressed-air supply however, the more powerful pneumatic road breaker is preferred. Therefore, this item was eliminated from the vehicle equipment.

The type of water pump fitted has not been found entirely suitable. The handling of 3-inch bore suction hoses, the necessity to prime the pump casing each time before use, and the disposal of the large volume of water pumped out were sources of difficulty and so this item was replaced by a pneumatic submersible pump. The latter is a compact, easily-handled item with adequate pumping capacity for general use. Also, it can be driven by the low-pressure compressor and it is cheaper than the 3-inch centrifugal unit. Removing the pump and alternator has simplified the hydraulic system and reduced costs.

FINAL DESIGN
The Rodding and Light-Cabling Vehicle, to be introduced nationally, will be a 5-ton payload vehicle with hydraulically operated mechanical aids and unit-construction racking.

The vehicle will have a coach-built body comprising a light-alloy framework with aluminium exterior panels. A translucent resin-bonded glass-fibre roof will ensure adequate illumination of the interior during daylight hours and four 15-watt fluorescent lamps provide artificial illumination. Exterior illumination, apart from normal vehicle lighting, will consist of flashing orange beacons front and rear and a floodlight arranged to illuminate the working area in the immediate vicinity of the rear of the vehicle.

The vehicle will have four built-in mechanical aids driven by the hydraulic system, two air compressors, one low-pressure and one high-pressure, a winch and a rod-pushing machine. These items will all be of the same design as those fitted to the prototype hydraulic vehicle.

The output of the low-pressure compressor will be piped to a live-centre retractable hose reel and the high-pressure compressor output to two smaller hose reels which will enable two ductmotors to be operated simultaneously. An air-blast oil cooler will be fitted to enable the capacity of the hydraulic reservoir to be reduced to 22 gallon compared with the 45-gallon reservoir fitted to the prototype. In addition to savings in cost, the smaller reservoir allows greater flexibility in siting it on the vehicle.

Instrumentation will be similar to that provided on the prototype vehicle except that no gauge is fitted to indicate system pressure. Instead, plug-in type pressure test points will be provided at each relief valve. Gauges to fit the test points will be held at maintenance workshops.

Careful attention has been paid to the layout of the system to provide good access to all components for maintenance purposes and all hydraulic pipes will be colour coded to indicate their function.

PRODUCTIVITY ASPECTS
The field trial of the Rodding and Light-Cabling Vehicle has shown that it offers a means of obtaining a substantial increase in productivity. Rates of work of 40 yd per man hour of duct rodded or cabled have been readily achieved and this compares favourably with the current national average performance of 13 yd per man hour for rodding parties and 25 yd per manhour for light-cabling.

FIG. 7 Cable-dispensing equipment

The improved performance offers the promise of a very satisfactory return on the capital invested in the vehicles. The use of a rodding machine with the combined capability of rodding and drawing-in cable has removed much of the hard labour and has brought the work to within the capacity of a two-man party. The use of appliances designed to operate in situ within the vehicle has eliminated much loading and unloading and considerably reduced the setting-up and closing-down time at work points.

However, not all the features contributing to increased productivity derive directly from the vehicle and its equipment. Of prime importance is the careful programming of work and adequate backing up by the supply organization to ensure that correct stores are available in time for carrying out programmed work. In this respect, a major factor is the provision of cable of the right size in the right length at the right time. To enable this to be achieved cable-dispensing equipment (Fig. 7) is being provided at section stocks serving Rodding and Light Cabling Vehicles. The equipment will be used to dispense measured lengths of cable from supply drums on to lightweight cable drums for issue to light-cabling parties. It is intended that cable for programmed work shall be available not less than 24 hours before it is required thus minimizing the time spent by working parties collecting stores. Rodding and light-cabling parties will carry their cable on a trailer which will carry up to three lightweight cable-drums each of which can, if required, contain a different type of cable.

CONCLUSIONS
The vehicles are being introduced into service over a period of about twelve months and training is programmed to ensure that trained crews are available in areas when vehicles are delivered.

The new system involves changes in local-line planning procedures for rodding and light-cabling work and the full effect of these will not be apparent until work in the pipeline is cleared.

ACKNOWLEDGEMENTS
Acknowledgement is made to staff in Telecommunications Headquarters, Regional Headquarters and Telephone Managers’ Offices for their part in the development of the Rodding and Light-Cabling Vehicles.

References:

  1. DEADMAN, D. J., and SLIGHT, J. R. A New Approach to the Duct-Rodding Problem - Ductmotor No. 1. P.O.E.E.J., Vol. 58, p. 91, July 1965.

  2. SULLIVAN, E. Polyvinylchloride (P.V.C.) Rods. P.O.E.E.J., Vol. 62, p. 124, July 1969.

  3. CHARLTON, E. W. Two New Cable-Drum Trailers. P.O.E.E.J., Vol. 61, p. 222, Jan. 1969.

  4. Press NOTICE. New Rod-Pushing Machine for Underground Cables. P.O.E.E.J., Vol. 62, p. 195, Oct. 1969.

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