With Existing Ducts Is the Key
by: Bob Young
Magazine 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?
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.
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.
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.
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?
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.
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.
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.
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
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.
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
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.
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.)
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
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
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.
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.
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."
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.
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."
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
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.
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.
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.
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, visit www.gmptools.com.