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106 en | Maintenance
Notice!
A hardware defect in the detector module is indicated by a permanently-lit detector module
LED.
8.4
Pipe system
Check the pipe system and the air sampling openings for obstruction in areas susceptible to
dust particles or icing. If necessary, blow out the pipe system and air sampling openings with
blast air. Use a mobile cylinder of compressed air (blowing-out system) or activate the manual
blowing-out system located on site. The components (compressors, compressed air
containers, dryers) required to supply the compressed air can be obtained directly from the
relevant compressed air system suppliers.
Caution!
Before blowing out the pipe system, disconnect the FAS-420 from the pipe system;
!
otherwise, the airflow sensor will be damaged.
Blowing out
The compressed air supply to the pipe system must be connected so that only the pipe system
itself is blown out. The aspirating smoke detector and the downstream accessory components
of the pipe system (e.g. air filter) must not and cannot be blown out.
A check valve must be installed at the end of each pipe branch. The check valve prevents
damage to the air sampling openings and prevents dirt deposits from being blown through the
pipe system. To prevent aspiration reducing film sheets in deep-freeze areas from tearing, it is
advisable to use special deep-freeze aspiration reductions.
The compressed air supply and compressed air connection must be installed so that at least
0.7 bar of pressure remains available per pipe branch within the pipe system. This means a
minimum of 0.7 bar for the I-pipe, a minimum of 1.4 bar for the U-pipe and a minimum of 2.8
bar for the double U-pipe. The minimum flow cross-section within the compressed air
connection must be taken into consideration. If the connection is made, e.g. via a quick
release coupler with a flow cross-section of 7.2 mm, an approx. pressure ratio of 1:9 occurs
due to the comparatively large flow cross-section within the pipe system (21.4 mm). If, for
example, 8 bar of pressure is available at the quick release coupler, this would drop to approx.
0.9 bar due to the larger flow cross-section in the pipe system. In this case, the pressure
would still be sufficient for an I-pipe system, but inadequate for U and double U‑pipe systems.
In plants where contamination of the pipe system/air sampling openings can be expected, the
compressed air supply can be connected via a three-way tap. In plants exposed to heavy
contamination (e.g. recycling plants) an automatic blowing-out system is recommended.
For areas exposed to moderate contamination, in which blowing out is required only at
prolonged intervals, the use of a mobile blowing-out system including refillable compressed air
cylinder is recommended.
8.5
Check the airflow sensor calibration
Check the airflow sensor value with the diagnostic software.
Functional principle
During initialization of the connected pipe system, the device saves the measured actual value
of the airflow as a target value via the integrated airflow monitoring. This nominal value then
serves as a reference value for the additional evaluation of a possible airflow malfunction.
Depending on the airflow threshold selected, the current airflow value during operation can
2020.04 | 6.1 | F.01U.029.275
Operation guide
Aspiration smoke detector LSN improved
Bosch Sicherheitssysteme GmbH
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