Chapter 4 • Pneumatic components – dimensioning
User Manual Series F-BO-AFE70
4
Pneumatic components – dimensioning
4.1
Purging unit
The geometry of the sampling pipe and the number and size of the aspiration holes depends on the
size and geometry of the room as well as the technical possibilities of the aspirating smoke detector
used. Thanks to the special construction of the Automatic Purging Unit F-BO-AFE70, it does not
cause an additional air resistance in the piping that is worth mentioning, and therefore it
does not
have to be taken into consideration when dimensioning
the pipe system.
Through intensive tests and experiments, the recommended values for dimensioning that are stated
below, have been established. Please note that the specified values are only approximate values
because a huge number of components (the length and the geometry of the pipe, the position of the
aspiration holes along the piping, the opening pressure of a check valve that may exist, etc.) affect
the Purging process. Therefore you can only make sure that the Purging unit is working properly by
carrying out a final test on the individual system.
First calculate the total aperture area of the aspiration holes that exist in the pipe network. In order
to keep the calculation simple, the table below shows the area of a circular hole, depending on its
diameter.
2.00
3.15
4.00
12.57
6.00
28.28
2.10
3.47
4.10
13.21
6.10
29.23
2.20
3.81
4.20
13.86
6.20
30.20
2.30
4.16
4.30
14.53
6.30
31.18
2.40
4.53
4.40
15.21
6.40
32.17
2.50
4.91
4.50
15.91
6.50
33.19
2.60
5.31
4.60
16.62
6.60
34.22
2.70
5.73
4.70
17.35
6.70
35.26
2.80
6.16
4.80
18.10
6.80
36.32
2.90
6.61
4.90
18.86
6.90
37.40
3.00
7.07
5.00
19.64
7.00
38.49
3.10
7.55
5.10
20.43
7.10
39.60
3.20
8.05
5.20
21.24
7.20
40.72
3.30
8.56
5.30
22.07
7.30
41.86
3.40
9.08
5.40
22.91
7.40
43.01
3.50
9.63
5.50
23.76
7.50
44.18
3.60
10.18
5.60
24.64
7.60
45.37
3.70
10.76
5.70
25.52
7.70
46.57
3.80
11.35
5.80
26.43
7.80
47.79
3.90
11.95
5.90
27.34
7.90
49.02
Diameter
[mm]
Area
[mm²]
Diameter
[mm]
Area
[mm²]
Diameter
[mm]
Area
[mm²]
Table 3:
Calculation aid for the determination of the total aperture area of the aspiration holes in the
sampling pipework; add up the stated values for the holes in the piping that is to be connected to
the Purging unit. The diameters that have been marked in
bold
in the table are the predetermined
standard values for the Series FAAST and VESDA.
The tables below show the operation limits of the Automatic Purging Units F-BO-AFE70-2 and
F-BO-AFE70-3, depending on the input overpressure during the Purging process and on the sum of
the aperture area of the aspiration holes of the piping that is connected to the Purging unit.
The data is based on a DN25 pipe network that has been realised as straight branch, and on a
check valve with an opening pressure of 25kPa (0.25bar) that has been installed at the end of the
pipe network. A safety factor has been added to the data and therefore it can be regarded as
approximate value for normal system configurations, but the proper functioning of the respective
system must always be verified in a test!
During the Purging process, the input overpressure decreases, depending on the quality of the
compressed-air supply and the air volume that is consumed. The input overpressure value listed
in the table is the
value when air is being consumed
, i.e., the decreased value!
I56-4252-010
D200-104-00
14
Summary of Contents for F-BO-AFE70 Series
Page 2: ......
