D500-08-00
4
I56-512-07R
In no case should more than 2 air inlet holes be cut off the
tube. There must be a minimum of 10 holes in the tube
exposed to the air stream.
B. Installation for Ducts More Than 8 Feet Wide
NOTE:
To install inlet tubes in ducts more than 8 feet
wide, work must be performed inside the air duct.
Sampling of air in ducts wider than 8 feet is accom-
plished by using the ST-10 inlet sampling tube.
Install the inlet tube as follows:
1. Drill a 3/4-inch hole in the duct directly opposite the
hole already drilled for the inlet tube.
2. Slide the inlet tube with the flange into the right hous-
ing bushing. Position the tube so that the arrows point
into the air flow. Secure the tube flange to the housing
bushing with the two #6 self-tapping screws.
3. From inside the duct, couple the other section of the
inlet tube to the section already installed using the 1/2-
inch conduit fitting supplied. Make sure the holes on
both of the air inlet tubes are lined up facing the air flow.
4. Trim the end of the tube protruding through the duct so
that 1 to 2 inches of the tube extends outside the duct.
Plug this end with the tube end cap and tape closed any
holes in the protruding section of the tube. Be sure to
seal the duct when the tube protrudes.
5. Any tube (over 3 feet long) that doesn’t protrude
through the duct (on the side opposite the housing)
must be supported by other means.
WARNING
AIR FLOW
DIRECTION
DUCT
DETECTOR
HOUSING
DOTS INDICATE POSITION OF
SAMPLING TUBE HOLES
AIR FLOW
DIRECTION
DUCT
DETECTOR
HOUSING
INLET
TUBE
EXHAUST
TUBE
AIR FLOW
DIRECTION
INLET
TUBE
EXHAUST
TUBE
INLET
TUBE
EXHAUST
TUBE
DUCT
DETECTOR
HOUSING
AIR FLOW
DIRECTION
EXHAUST
TUBE
INLET
TUBE
DUCT
DETECTOR
HOUSING
Figure 4. Tube mounting configurations with varying air flow direction and orientation of detector housing.
Vertical as well as horizontal mounting is acceptable.
A78-1812-01
NOTE:
An alternate method to using the ST-10 is to use
two ST-5 inlet tubes. Remove the flange from one
of the tubes and install as described above. After
the installation, use electrician’s tape to close off
some of the sampling holes so that there are a total
of 12 holes spaced as evenly as possible across the
width of the duct.
NOTE:
Air currents inside the duct may cause excessive
vibration. This vibration can slowly open the seal
around the tube and permit air to escape. To pre-
vent this from occurring, a 3-inch floor flange,
available at most plumbing supply houses, may be
used. This flange/connector mounting technique
makes the initial installation easier because a 1-
inch to 1-1/4-inch hole may be drilled where the
flange/connector will be used. It is easier to push
the inlet tube through the larger hole.
Modification of Inlet Sampling Tubes
There may be applications where duct widths are not what
is specified for the installation. In such cases, it is permis-
sible to modify an inlet sampling tube that is longer than
necessary to span the duct width.
