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:-
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rods are used to reach the next joint box and a draw rope is attached and then pulled into the duct as the rods are withdrawn.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
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.
Cane rods being used by a cabling team.
Continuous rod on a frame
Continuous rod in use
Rods, Duct No. 3
Duct Motor about the start work
The compressor is in the back of the vehicle
The Duct Motor is in front of the manhole
Early Duct Motor
Complete Duct Motor kit
Duct Motor No. 2B
Last revised: April 18, 2023