VDOT-ASD-100 Aspiration Detector
Velocity Detection
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VDOT-ASD-100 Aspirating Smoke Detector User’s Manual V1
Sampling Pipework Design
Aspirating system design is inherently simple. It is often possible to achieve good system
performance with very simple installations. There are however a few rules, which must be
adhered to, and these rules are equally applicable to all aspirating systems. The information
contained in this manual is intended as an overview only. For further information please see
the complete Velocity ASD Design Manual.
Considerations
o
Primary Detection Sampling Systems
Are usually arranged to monitor the flow of air movement by the use of pipework and air
sampling points mounted directly in the airflow. This type of system is usually regarded as
supplementary to other forms of detection due to its limited response capability once the
air movement ceases.
In such a system when monitoring a single point of supply or extract, its system sensitivity
may be directly related as equal to the sensitivity of the central detector due to the
cumulative effect. In the case of a system monitoring more than one point of supply /
extract then the system sensitivity will only be determined in discussions with the
manufacturer or his representative.
Always locate the sampling points in a position to which smoke may reasonably be expected
to travel. This may sound obvious, but, for example, do not expect ceiling mounted sampling
points to operate satisfactorily if air flow prevents the cool smoke from an incipient fire from
reaching ceiling level. In this instance it is usually better to locate the sampling pipes directly
in the airflow (for example in an air conditioning unit air intake). There is no substitute for
carrying out smoke tests prior to installation of pipes to indicate suitable sampling point
location.
o
Secondary Detection Sampling Systems
Are arranged such that the air sampling points are sited and spaced as if they are point type
smoke detectors. They can be positioned to satisfy NFPA 72, NFPA 76, BS 5839-1, BS 6266
