Xtralis VESDA VLC-505, Manual

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VESDA Pipe Network Design Guide VESDA by Xtralis
42 www.xtralis.com
9.2 Maximum Transport Time
Maximum transport time indicates the longest time taken for smoke to travel from a sampling hole to the
detector. You should aim to get the lowest possible time without compromising on the Hole % Balance and
the Hole % Share values.
Note: Subject to local codes and standards the maximum transport time is 120 seconds. We recommend
the maximum transport time of less than 60 seconds when early warning is desired.
Pipe lengths affect the time to transport a sample of air from the collection point to the detector. Factors like
bends, diameter of sampling holes and endcap holes also affect the transport time. Figure 10-1 on page 43
illustrates how the same area can be covered by different pipe lengths.
9.3 Hole Sensitivity
The relative sample hole sensitivity is a measure of the sample hole in relation to the detector’s fire threshold
sensitivity. Mathematically it is presented as:
Detector Sensitivity / (Sample hole flow / Sum of all sample point flows) = % obs/m (%obs/ft)
= 2.0% Obs/m
Detector Sensitivity
Sample Hole Flow / Sum of all Sample Point Flows
0.1
0.05
=
Figure 9-2: Hole sensitivity