GPO Vehicles

Make Commer
Model Walk Thru
Body Builder Trombi Rodder Air Van
Use Rodding Vehicle
Registration Number NYV 828E
Fleet Number 202381
Date of Vehicle January 1968

A prototype 'Air-Van'. This is based on a Commer 'walk-through' chassis with a power take-of driven air compressor.


Development of New Rodding Equipment
Taken from External Plant News - No. 8 April 1968

As there have been several field trials of rodding equipments the following is a review of the problems and progress that has been made.

Rodding problems
The rodding of a duct is still and probably always will be, a doubtful operation because of the wide variation of duct conditions. The causes of difficulty are:-

  1. The condition of the duct, that is has settlement, damage or silt, caused partial or complete blockage?
  2. The number and size of cables already in the duct.
  3. The access position; are buried couplings involved?
  4. Local flooding.
  5. Traffic conditions.
  6. The grease remaining in the duct from previous cable operations.

It should be noted that all new ducts will have a draw-rope which has been inserted by the contractor.  The draw-rope is highly resistant to conditions in the duct and should remain usable for many years, and will have a breaking strain of 1200 lb.  Each new cable will have a draw-rope drawn-in with the cable, if there is space in the duct for any further cable. This will mean that a better type of swivel is required since the present one does not operate well on small loads.  There is a new type of swivel on field trial at present. (See also article on Connectors Swivel in this Issue.)

Rodding methods
(a) The ductmotor is a good device provided that the following points are considered:-

  • There should be at least 2 in. diameter space available in the duct, that is if it is not already too full for the ductmotor to pass.
  • That there is no heavy silting.
  • No sharp bends in the duct line, or at boxes.

The ductmotor causes less damage than any other device, and a good supply is available.

(b) The use of cane rods has been superseded by PVC which is much better to handle has lower friction in the duct but is still subject to a PVC phenomenon, known as 'cold shatter' at low temperature. The PVC rods (Rods Duct Nos. 1 and 2) are being supplied in 9 ft. lengths for rodding parties and 6ft. lengths for jointers and can be carried in 15 cwt. vehicles.

It is possible to extrude PVC in long lengths and six hundred lengths of 200 yards on the new type of reel are on order, for use instead of steel. These reels must be mounted in the vehicle. The PVC rod has a hollow section and can be used to carry a water jet or air, under pressure, for silt clearance.

The PVC rod can be used in a space of just over 1 in. diameter, and the development of a machine to push the continuous PVC rod is in hand.

(c) Continuous Steel Rods. The b in. diameter steel rod can be pushed by hand or by machine.

  • The reciprocating machine, which uses grips to push the rod in short moves was manual but is now operated by a cornpressed air piston, powered from the ductmotor compressor.
  • The Mangle Machine, which grips the rod between two grooved rollers, is driven by either a small petrol engine, or an electric motor. This method has been developed in Scotland.

Proposed Equipment Arrangements
That all equipment must be mounted in working positions in a suitable vehicle so that no time or effort is wasted in setting up the work. Also work can continue in rain or snow, since the operator can use the rodding equipment in the vehicle.

Where the vehicle cannot park at or near enough  to the box (at either end) the party will use 9 ft. PVC rods by hand. (Two men can push 180 yards with these rods.)

A recommended fitting layout for 30 cwt. and 2 ton Utility vehicles has been issued by OP Branch.

To avoid damage risk to existing cables, particularly coaxial, the ductmotor will be tried wherever there is a 2 in. space available. To make the best use of the equipment each 2-man rodding team will be issued with four ductmotors -two with large bags and two with small - so that by setting up at one box the duct route can be rodded forwards and backwards at the same time.  Provision of ductmotors allows for this and the 15 cu. ft. compressor provides sufficient air. If there is insufficient duct space for operating the ductmotor then a continuous rod will be used.

The 5/16 in. diameter steel continuous rod can generally be pushed only about 135 yards and then must be carried from the other end.  The PVC continuous rod and the PVC 9 ft. rods can often be pushed 180 yards depending on the state of the duct.

Future Equipment Design
In view of the various tasks which can fall to the rodding party and the various equipments necessary
to carry them out, it appears that compressed air is the most attractive universal drive for the following task:-

  1. Digging out a buried box or coupling - use a pneumatic digging tool.
  2. Pump out box or manhole - use compressed air water pump.
  3. Break-down to obstruction in footway or carriageway - use pneumatic digging tools.
  4. Driving the ductmotor.
  5. Driving, by an air-motor, either the reciprocating or Mangle rodding machine.
  6. Clearance of silt - by using compressed air driven silt clearance equipment - as an optional extra.
  7. Driving a light winch - by an air motor.
  8. Air motor drive to re-reel the ductmotor hose.

Whilst these devices can individually be driven by other motive power, air power is convenient. It is possible to get this air-power from a new type of compressor mounted under the vehicle floor and driven from the vehicle engine, and this is commercially available at a reasonable price.

This concept is considered to be the specialist duct-rodding vehicle of the future and a prototype is being fitted out. The savings achieved would be:

  • Time in starting up auxiliary motors
  • In space by eliminating the auxiliary motors
  • In capital cost by having one compressor on a 'Power Take Off', this is cheaper than the several motors now used.
Reciprocating type rod pushing machine which can be used on steel or PVC continuous rods.
Interior view of prototype air-van. The air compressor is under the vehicle floor and is powered by the vehicle engine,
The continuous PVC rod reel which is a permanent fixture in the vehicle. Water/air can be forced down the rod under pressure to clear obstructions in the duct lines.
Air-powered winch in the air-van, which pulls in small diameter cables by means of the draw-rope. The draw-rope is wound on to a power driven reel above the winch.  An air hose reel can be seen above the draw-rope reel.


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