Working With Existing Ducts Is the Key
Wouldn’t it be great if there were a convenient way to pull cable in existing conduit systems that already have cables in them? Particularly in old downtown areas where the conduit systems might be constructed from any variety of old materials such as tile, clay pipe, or even wood?
There are countless 3- to 4-inch ducts already in place that only have one or two small cables in them. That leaves plenty of extra space for something else. A fiber optic cable, or a micro duct and cable, would take up very little room in a conduit.
The problem, however, is that old conduit systems are not necessarily easy to pull cable through. Easily damaged materials like tile, clay, and wood were often used to construct conduits in a number of major U.S. cities. As a result, a host of issues, like damaged or broken ducts to build-ups of mud or silt, can make pulling cable a difficult and time-consuming process.
Hand rodding, unfortunately, is very labor intensive. Besides being slow and difficult, the work typically requires two men in the vault to push the rod and often another above ground. This is still the method of choice however, because pulling rod is less expensive and time-consuming than having to replace old conduits.
Conduit replacement not only means the difficulty of accurately locating conduit blocks and an arduous digging process, but it can also lead to drastic traffic disruptions in major metropolitan areas. So how can cable be pulled in old or damaged conduits quickly and easily?
AECON Infrastructure, Ontario, Canada, faced this situation recently when it was selected by Bell Canada to pull new fiber optic cable through several existing conduits in various metropolitan areas throughout Ontario. The entire project covered some 30,000 meters (about 90,000 feet) of conduit.
Bill Fuller, supervisor for AECON, and no stranger to this kind of work, knew what challenges he might face in trying to pull cable through old and damaged ducts. Fuller has tackled these assignments with many different methods in the past. He might, for example, try to blow a parachute through the duct using a compressor. When that didn’t work, it would be time to break out the duct rodder and begin the physically draining task of trying to push the fiberglass rod through.
Fuller considered purchasing or renting a rodder truck for this particular job in order to avoid the difficulties of hand rodding. But a rodder truck is a powerful machine. It is so powerful that there is just too much potential to damage working cables in old conduits. In some cases, the cables are old lead cables with companion air pipes. The risk of damaging working cables, combined with the high operating costs of the big machine, caused him to reject the idea, leaving Fuller still stuck with no solution.
"I was trying to find something less expensive than a rodder truck because the project really didn’t cover the cost of a rodder truck," Fuller says. "So I was searching for something halfway in between, or cheaper, other than pushing the rod by hand."
While looking for a way to reduce the physical strain of the operation and somehow improve efficiencies, Fuller’s search led him to General Machine Products (GMP), of Trevose, Penn. At the time GMP had been working to expand the capabilities of its Tornado Cable Blowing Machine. Because the principal of pushing a duct rod is very similar to that of pushing cable into a duct, only a few modifications were necessary for the Tornado for it to be able to power a duct rod from a standard duct rod cassette.
Those key modifications included adding higher torque motors, a forward and reversing valve, and a rod-length counter that counted out and subtracted back. Additionally, a feeder pipe adapted between the machine and the rod cassette allowed for worry-free and hands-free re-coiling of the rod onto the cassette. Of course, the components on the Tornado that provided the pressurized air to propel the cable were removed for the powered duct rodder.
No Underestimating This Workout
AECON’s project provided the perfect test to give GMP’s prototype machine a real workout. 30,000 meters (about 90,000 feet) of old conduit in a number of metropolitan locations is no small task. The job also provided a platform to discover what other changes might be added to further enhance the machine’s viability for this type of application.
In about two hours on the first day, nine duct sections had been rodded. Three of those nine sections were blocked; one broken and the others silted up solid. Later on that first day, the powered duct rodder was used to rod a nearly 1,000-ft section that had a 200-pair lead cable, an air pipe, and a fiber optic cable in the duct. (See Figure 1.)
An unanticipated benefit to using the powered duct rodder, one that may ultimately be more valuable than any, is a reduction in work-related injury claims. Hand rodding is very laborious work, often shoulder-straining and backbreaking.
"When you start pushing these things by hand every day or every other day," Fuller says, "people start getting shoulder and back injuries. We’re trying to get away from that, trying to find something where it was done mechanically to cut the cost of work injuries."
Fuller found his much needed mechanical assistance in the powered duct rodder. The rodder’s deployment and retraction of rod cut down on the strenuous labor associated with hand pulling. Not only that, but the rodder could help to reduce work-related injuries.
According to Ted Kyle, AECON’s Regional Safety Manager, the company averaged three medical aids per month, with the cost to process each claim averaging $5,000.00. The company is deeply interested in reducing these claims and the risks associated with this type of work. If the results of the field trial continue, the powered duct rodder may prove to be a major factor in that regard.
The powered duct rodder proved exceptionally adept at handling the problems commonly encountered with existing conduit, Fuller explains. “Going through old conduit,” he says, “we found repairs that weren’t done properly. Or, we found tree roots growing in them, or just mud. And the idea of this machine was just to help us find those blockages so we could start repairing damages to the conduit.”
The counter on the rodder also impressed Fuller, because this device helps to pinpoint conduit obstructions. As the rod feeds into the conduit, the counter indicates how far out the rod has gone. This measurement indicates precisely where the blockage is so the crew can make the necessary repairs.
“When we were doing it by hand,” Fuller explains, “we’d push it in by hand, pull it back out by hand, pull the fish tape out and stretch it across the ground so you know where you were at. That’s time consuming and physically hard on the guy who has to do it every day. And there are places you can’t do that, such as across an intersection or a driveway.”
Fuller was extremely happy with the results of his crew’s three-day trial. Previously difficult conduits were much more manageable with this prototype. Now, it’s ready to go into the marketplace. Several other options will be available on future production models. One example will be a wiping mechanism to help clean the rod of debris as it is retrieved out from the duct. This helps to prevent mud and silt, etc., from entering the machine.
Another feature includes an electronic sonde that can be attached to the front end of the rod, allowing for radio tracking by an aboveground receiver. This sonde can also be equipped with a GPS tracking system, which will allow for easy and accurate locating of conduit blocks.
More importantly, however, this GPS will allow workers to generate precise and detailed maps for conduit systems where the originals have been lost, or for conduit systems that have changed over time. This means workers will no longer have to rely on inaccurate or dated maps because they can easily create their own. Old, antiquated conduit systems will no longer be a mystery.
With this system, a worker can even use signals sent from the sonde to plot the GPS points in a computer. Then, a printout of the conduit route can be produced. This printed version can actually show the conduit route on a pre-loaded, to-scale street map making finding precise points above ground an extremely simple process.
About the Author
Bob Young is the Sales and Applications Engineer at General Machine Products Company (GMP). He has more than 30 years of experience in the telecommunications industry. For more information, visitwww.gmptools.com.