Bosch FAS-420-TT Series - Length Change of the Pipe System

86 en | Installation of the pipe system Aspiration smoke detector LSN improved
2020.04 | 6.1 | F.01U.029.275 Operation guide Bosch Sicherheitssysteme GmbH
3. Minimize pipe lengths and changes of direction. Pipe elbows have an extremely high flow
resistance. Therefore, they should only be used where they cannot be avoided for
structural engineering reasons. If necessary, reduce pipe lengths in proportion to the pipe
elbows used.
Notice!
Pipe bends must be given preference over pipe elbows. Too many bends and pipe elbows
reduce the air speed in the aspiration pipe, thereby increasing the detection time.
A 90° pipe elbow corresponds to a straight pipe length of 1.5m. Because of this, the
maximum total length of the pipe system is reduced by 1.5 m.
4. Fix the pipe system. It must not sag or be possible to move it. Fasten the pipes with pipe
clips without rubber inserts. The distance between the pipe clips should not exceed
80cm. At high temperatures, reduce the distance between the pipe clips to a maximum
of 30cm.
Notice!
Do not use pipe clips with rubber inserts since these do not allow length extensions and the
pipe system could thus bend or even tear.
5. Close open pipe ends with an end cap.
Notice!
On completion, test the pipe system:
For tightness
For fault-free connections
For correct planning of the air sampling openings.
6.1 Length Change of the Pipe System
Length changes (extensions and reductions) of the pipes are caused by temperature changes.
Temperature increases cause lengthening of the pipes, temperature drops cause shortening of
the pipes. The length change must be given particular consideration if the temperature of the
pipe system at the time of installation deviates from the normal operating temperature.
The length change can be calculated using the following formula:
where
ΔL = Length change in [mm]
L = Length of the pipe to be calculated in [m]
ΔT = Maximum temperature difference in [°C]
δ = Length change coefficient in [mm/m x °C]
δPVC = 0.08mm/m x °C
δABS = 0.101mm/m x °C
For example, a temperature change of 10°C on a 10m-long PVC pipe causes a length change
of 8mm.
Mounting clamps
PVC pipe clips are used as standard for installing the pipe system. These clips do not allow
any length extensions.