14 Conventional Products—DH400 Conventional Air Duct Smoke Detector
An alternate method to using the ST-10 is to use two ST-5 inlet tubes:
1.
Remove the flange from one of the tubes, and install as described
above.
2.
After the installation, use electrical tape to close off some of the
sampling holes so that there are a total of 10 to 12 holes spaced as
evenly as possible across the width of the duct.
Air currents inside the duct may cause excessive vibration, especially
when the longer sampling tubes are used.
In these cases:
1.
Use a 3 inch floor flange (available at most plumbing supply stores) to
fasten the sampling tube to the other side of the duct.
2.
When using the flange/connector mounting technique, drill a
1 to 1-1/4 inch hole where the flange will be used.
There may be applications where duct widths are not what is specified for
the installation. In such cases, it is permissible to modify an inlet
sampling tube that is longer than necessary to span the duct width.
1.
Use a 0.193 inch diameter (No. 11) drill.
2.
Add the appropriate number of holes so that the total number of holes
exposed to the airflow in the duct is 10 to 12.
3.
Space the additional holes as evenly as possible over the length of
the tube.
This procedure should only be used in an emergency; it is not intended as
a permanent substitute for ordering the correct length tubes.
Interim
Modifications of
Inlet Sampling
Tubes
