FIGURE 3. AIR DUCT DETECTOR SAMPLING TUBE
SAMPLING TUBE ENDCAP
ARROW MUST FACE
INTO AIR FLOW
AIR FLOW
DIRECTION
H0551-00
CAUTION:
The sampling tube end cap, included with the detector, is criti-
cal to proper operation of the duct smoke detector. The end cap is needed to
create the proper air flow to the sensor of the duct smoke detector. Once any
sampling tube length adjustments are made, plug the end of the sampling tube
with the provided end cap.
A plastic exhaust tube is included with the unit. Install into the housing con-
nection that is downstream from the sampling tube connection. The exhaust
tube can be installed from the front of the detector or the back. A longer 1
foot exhaust tube, model ETX, is available as an accessory in cases where the
molded exhaust tube does not extend at least 2 inches into the duct.
[5.2] SAMPLING TUBE INSTALLATION
1. For tubes shorter than the width of the duct, slide the sampling tube,
with installed end cap, into the housing connection that meets the air-
flow first. Position the tube so that the arrow points into the airflow as
shown in Figure 3. Per NFPA sampling tubes over 3 feet long should be
supported at the end opposite of the duct detector. In ducts wider than 8
feet, work must be performed inside the duct to couple the other section
of the sampling tube to the section already installed using the ½-inch
conduit fitting supplied. Make sure that the holes on both sections of the
air inlet sampling tube are lined up and facing into the airflow.
2. For tubes longer than the width of the air duct, the tube should extend
out of the opposite side of the duct. Drill a ¾-inch hole in the duct op-
posite the hole already cut for the sampling tube. Ensure that the sam-
pling tube is angled downward from the duct smoke detector to allow for
moisture drainage away from the detector. The sampling tube should be
angled at least ¼˝ downward for every 12˝ of duct width per Figure 4.
There should be 10 to 12 holes spaced as evenly as possible across the
width of the duct. If there are more than 2 holes in the section of the tube
extending out of the duct, select a shorter tube using Table 1. Otherwise,
trim the tube to leave approximately 1 to 2 inches extending outside the
duct. Plug the end with the end cap and tape closed any holes in the
protruding section of the tube. Be sure to seal the duct where the tube
protrudes.
FIGURE 4.
DETECTOR
3
/
4
˝
HOLE
12˝
1
/
4
˝
2˝
H0215-00
NOTE: Air currents inside the duct may cause excessive vibration, especially
when the longer sampling tubes are used. In these cases, a 3-inch floor flange
(available at most plumbing supply stores) may be used to fasten the sam-
pling tube to the other side of the duct. When using the flange/connector
mounting technique, drill a 1 to 1¼-inch hole where the flange will be used.
[5.3] MODIFICATIONS OF SAMPLING TUBES
There may be applications where duct widths are not what is specified for the
installation. In such cases, it is permissible to modify a sampling tube that is
longer than necessary to span the duct width.
Use a 0.193 inch diameter (#10) drill and add the appropriate number of holes
so that the total number of holes exposed to the air flow in the duct is 10 to 12.
Space the additional holes as evenly as possible over the length of the tube.
CAUTION:
This procedure should only be used as a temporary fix. It is not
intended as a permanent substitute for ordering the correct length tubes.
[5.4] REMOTE SAMPLING TUBE INSTALLATION
The detector arrangement can also incorporate the remote mounting of the
sampling tube and/or exhaust tube. In this case both the detector, sampling
tube and exhaust tube (if included) should be rigidly mounted to withstand
the pressure and vibrations caused by the air velocity. The location of the
detector’s sampling tube should be such that there is uniform airflow in the
cross section area.
Pressure differential across the sampling and exhaust ports in the detector
housing shall be verified to be between 0.01 and 1.11 inches of water. Do so
by measuring the pressure difference between the inlet and outlet ports on the
detector housing using a manometer as described in Section 6 Measurement
Tests.
[6] MEASUREMENT TESTS
[6.1] AIR FLOW
The DNRA is designed to operate over an extended air speed range of 100 to
4000 FPM. To verify sufficient sampling of ducted air, turn the air handler on
and use a manometer to measure the differential pressure between the two
sampling tubes. The differential pressure should measure at least 0.01 inches
of water and no more than 1.11 inches of water. Because most commercially
available manometers cannot accurately measure very low pressure differen-
tials, applications with less than 500 FPM of duct air speed may require one
of the following: 1) the use of a current-sourcing pressure transmitter (Dwyer
Series 607) or 2) the use of aerosol smoke, see below for test descriptions.
FIGURE 5. PROCEDURE FOR VERIFYING AIR FLOW
HIGH
LOW
9 VOLT
BATTERY
9 VOLT
BATTERY
9 VOLT
BATTERY
TO SAMPLING TUBE
TO EXHAUST TUBE
DIFFERENTIAL
PRESSURE
TRANSMITTER
MODEL #607-01
15 TO 36
VDC SUPPLY
1000 OHM 5%
1 WATT RESISTOR
VOLT METER FLUKE
MODEL 87 OR
EQUIVALENT
+
–
H0163-01
[6.2] LOW FLOW AIR FLOW TEST USING DWYER SERIES 607
DIFFERENTIAL PRESSURE TRANSMITTER
Verify the air speed of the duct using an anemometer. Air speed must be
at least 100 FPM. Wire the Dwyer transmitter as shown in Figure 5. Con-
nect the leads of the meter to either side of the 1000
Ω
resistor. Allow unit to
warm up for 15 seconds. With both HIGH and LOW pressure ports open to
ambient air, measure and record the voltage drop across the 1000
Ω
resistor
(measurement 1), 4.00 volts is typical. Using flexible tubing and rubber stop-
pers, connect the HIGH side of the transmitter to the sampling tube of the duct
smoke detector housing, and the LOW side of the transmitter to the exhaust
tube of the duct smoke detector housing. Measure and record the voltage drop
across the 1000
Ω
resistor (measurement 2). Subtract the voltage recorded in
measurement 1 from the voltage recorded in measurement 2. If the difference
is greater than 0.15 volts, there is enough air flow through the duct smoke
detector for proper operation.
3
I56-3104-004
4/18/2019
