UNDERGROUND CONSTRUCTION
RODDING DUCTS

Rodding ducts is done for many reasons and there are also different types of rods used. Originally there were the cane rods which screwed together (like a chimney sweeps except longer) followed by screwed together plastic rods, then came continuous rods and finally the Duct Motor (an air driven device).

What use is a duct rod:-

To locate a blockage.
To check for blockages.
To lay a draw rope.

When checking for blockages an iron mandrel is pulled up and down the duct by a rope attached to both ends. They were made a quarter of an inch smaller diameter than the diameter of the duct and will stop if there are breakages. Click here for a picture of a modern mandrel.

A cylindrical brush was also available for cleaning the internal surface of the duct and this would be drawn through be means of a draw rope.

When cables are laid a rope is normally attached and left in the duct, with the cable, in case another cable requires to be drawn in at a later date.

Where there is no draw rope, rods are used to reach the next joint box and a draw rope is attached and then pulled into the duct as the rods are withdrawn.

Continuous rods could also be used with the Machines, Rod, Continuous - Click here for Lines, Underground F3041

The Duct Motor is driven by air from a compressor. The Motor itself is a piston with two rubber bulbs, one at each end. The air expands the back bulb and the piston expands pushing the front bulb forward. The front bulb expands, the back bulb deflates and the piston then contracts pulling the back bulb forward. It does continuously, moving up the duct until it reaches the other end.

Click here for a document on Duct Rodding Equipment - Tools and Transport, Hand Tools R1250
Click here for a document on Duct Rodding Equipment - a2d3055

Rodding in ducts - Lines, Underground F3040

Duct Motor - Operation and Maintenance - Lines, Underground F3042

Use of Rodding and Light Cabling Vehicle - Lines, Underground F3045

Rods, Duct No. 1 - Length 3m PVC.
Rods, Duct No. 2 - Length 2m PVC.
Rods, Duct No. 3 - Continuous length 250m PVC rod of 24mm diameter. Used only on the Rodding and Light cabling vehicle.
Rods, Duct No. 4 - Length 9'.
Rods, Duct No. 6A - Length 1m.
Rods, Duct No. 6B - Length 3m.
Rods, Continuous - Length 600'.