VESDA by Xtralis VESDA PipeNetwork Design Guide
www.xtralis.com 9
4 Air Sampling Methods
Site requirements and conditions determine the best sampling method. Local codes and standards may have
a bearing on the selection of sampling methods used. Air from an Address (Zone) is drawn through sampling
holes in the pipe network. The pipe network transports the sampled air to the detector. The position and
spacing of sampling holes is dependent upon the pipe network design. Refer to Table 4-3 on page 25 for
examples of sampling methods that can be used for various applications.
There are three basic air sampling methods (as described below). Typically, a site will use more than one.
4.1 Standard Pipe Sampling
These guidelines are used for all pipe network designs. In addition, guidelines specific to different sampling
methods may also apply. Refer to Chapter 8 for further information.
1. Parameters and values specified in your local codes and standards have precedence over anything
suggested in Xtralis documentation.
2. We recommend smooth bore pipe with 25 mm OD and 3/4 inch IPS internal diameter. The preferred
CPVC, PVC, ABS or UPVC pipe internal diameter is 21 mm (0.874 in).
3. Maintain at least 500 mm (20 inches) of straight pipe before the pipe terminates at the detector.
4. Use bend or elbow connectors to change the direction of the pipe. Bends maintain better airflow than
elbows.
5. All sampling pipes should be fitted with an endcap. Use the ASPIRE2 software to assist in determining
the size of the hole in the endcap.
6. For optimum detector performance you should keep pipe runs to a similar length.
7. For optimum detector performance you should keep a similar number of holes in each pipe.
8. It is better to use multiple pipes of shorter total length, than a single pipe of longer length.
A simple grid layout can be used to suit most rectangular spaces. Refer to Section 6.1 on page 29 for further
information.
4.2 Capillary Tube Sampling
Capillary tubes are used to sample air some distance away from the sampling pipe and in enclosed areas like
cabinets. The guidelines for capillary sampling are:
1. When possible use capillaries of the same length.
2. The maximum capillary tube Internal Diameter (ID) should be 5 mm (3/8 in.).
3. Maintain balance within the pipe network by using the ASPIRE2 software to determine the size of the
sampling hole required
4. Capillary tubes should not exceed 8 m (26 ft).
5. The positioning of the sampling hole for in-cabinet sampling is dependant on air flow conditions. In most
instances the sampling hole is positioned close to the top of the interior of the cabinet. Refer to Figure 4-
16 on page 17 for further information.
If you wish to use capillary sizes outside these guidelines then please use the ASPIRE2 software to check
that you will still have an acceptable design.
4.3 Open Area Protection
4.3.1 On-ceiling Sampling
Typically the pipe network is suspended approximately 25 mm to 300 mm (1 in to 1 ft) below the ceiling in the
area to be protected.
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