A smoke ducting system consists of one or more smoke machines, and some
ducting, if it is an "active" system it also includes an air blower. The
blower is usually contained in a metal fabricated housing the Distribution
Box or Expansion Box. In an active system, the smoke machine can be directed
into the intake side of the expansion box without any ducting at all.
An expansion box may have (as ours does) a 4" flange on the output side
that couples with a 4" duct. The intake side has an open 4" port without
a flange that draws smoke from the output of the smoke machine. The suction
from the air blower is sufficient to draw all the smoke that the smoke
machine can deliver without being coupled directly to the expansion box.
The expansion box is large enough to act as a smoke reservoir. From the
expansion box, the ducting is routed from the output of the box throughout
the area to be covered with smoke. An illustration showing the basic components
of an active smoke ducting system is at right.
An excellent material to use for smoke ducting is ADS drainage hose (Advanced
Drainage Systems, Columbus, Ohio, 800/733-7473). ADS is a durable, flexible,
ribbed 4" hose normally used for irrigation and drainage systems. It easily
attaches to other components with RTV silicon rubber. There are several
fittings made by ADS, like couplers, "T" fittings, 90 degree fittings,
end caps, etc., that can be used to design complex ducting systems. ADS
hose is very reasonably priced and usually easy to find. It is normally
stocked in nursery supply outlets and retail hardware and lumber stores
in most metropolitan areas of the United States. Other types of ducting:
Larger diameter ducts provide less resistance to the flow of smoke and
are recommended for large volumes of smoke and/or a long run of duct,
dryer hose is not recommended, it is not nearly as durable as ADS. A good
smoke expansion design should take into consideration the airflow of the
room... the location of the air conditioning registers. The smoke should
be discharged at a location farthest away from the air conditioning intake
for maximum smoke effectiveness.
The air conditioning registers (output) will tend to stir up and dissipate
the smoke. The ducting may be branched off in order to deliver smoke to
different locations. A duct may extend one or two hundred feet or more
provided the proper air blower is used. The longer the run is, the longer
the delay will be between enabling the smoke machine and the delivery
of the smoke. Typically, a one hundred foot tube (duct) will take a few
seconds for the smoke to come out. Under normal circumstances, a large
volume of smoke will pour out of the end of the ducting even if the ducting
is perforated.
Delivering Smoke to various locations
Perforations in the ducting help deliver smoke if it is needed along the
route of the ducting, rather than dumping the entire contents out of the
end of the duct. A perforated tube acts much like a sprinkler system for
smoke. ADS ducting is durable, yet lightweight enough to be easily perforated
with a pocketknife or a cordless drill. A drill bit makes a big enough
perforation to deliver smoke, the bigger the hole the more smoke at that
location. It's best to start with an unperforated tube. Turn on the system
and begin perforating, then examine the results to see if more perforations
are needed and if the perforations are delivering the proper amount of
smoke to the proper locations. Keep in mind that each perforation causes
a slight drop in pressure along the length of the tube. Therefore, the
perforations should be larger in diameter and greater in number farther
away from the air blower to get the same volume of smoke at the end. The
end of the ducting can be capped to help maintain pressure along the entire
length of the tube.
Over time, smoke fluid will tend to condense inside the ducting because
it cools as it is being delivered. ADS is ribbed, so the excess smoke
fluid will collect in the ribbing. However, if the ducting is installed
in a sloping fashion, gravity will cause the fluid to drip through perforations,
if perforated. Therefore, it is best to design the slope towards the blower
in order to force the excess smoke fluid to collect in the expansion box
rather than on the floor. In a fixed installation, it is recommended that
every year or so, you check and drain the expansion box.
American Safety ASHP
(1-888-BUY-ASHP,
www.buyashp.com)
markets an expansion box tailor
made for permanent installations. It is constructed of galvanized aluminum
and is supplied with a 4" flange for coupling to ADS. The air blower is
a squirrel-cage fan that delivers 495 cubic feet per minute under no-load
conditions. It can be ordered for 115V at 50/60 Hz or for 230V at 50/60
Hz operations. The blower mounts on the inside of the expansion box with
four bolts. The mounting holes are pre-drilled in the expansion box for
convenience. To assemble the expansion box simply insert the flange from
the inside of the box using RTV silicon to form a seal between the box
and the flange, then place the flange of the air blower over the expansion
box flange and bolt in place. The inside of the expansion box is easy
to access because the entire lid is a separate piece that can be removed
without the use of tools.
Once the air blower is mounted, it must be wired to the mains supply.
A good method of wiring it is to use a Greenlee punch and punch a hole
in the sheet metal large enough to mount a junction box. Then, conduit
can be run to the junction box and back to the relay panel or other switching
device (such as an ordinary light switch). The blower draws about 3.25
amps and medium size smoke generator draws about 14 amps at 115VAC. They
can both be supplied from the same 20-amp circuit provided there are no
applicable de-rating factors (in the United States, refer to the National
Electrical Code or to local regulations). The dimensions of our smoke
expansion box are given in the diagram for reference.
Once the system is installed and the electrical connections made, the
smoke machine and the air blower can be powered up at the same time and
kept on continuously. One of the advantages of building a smoke distribution
system is that it allows the smoke machine to be located in an area with
convenient access for changing fluid containers and for maintenance. Avoid
locating a smoke machine over people's heads or directed at a high traffic
area with a smooth floor, it can get slippery. Smoke machines produce
very hot particulate that could spew onto someone. It's also a lot more
difficult to service a smoke machine on a ladder than in an electrical
closet. By using a distribution/expansion system, the smoke machine may
be located in the most convenient place.
