Table of Contents
Advertisement
16
Chapter 4 • Pneumatic components – dimensioning
There is a tool based on a spreadsheet which makes this dimensioning easier. In order to use it,
you need the following parameters:
- Ambient temperature
- Number of aspiration holes
- Diameter of aspiration holes
- Air vessel overpressure
- Actual input overpressure
The compressed air must always be clean and free from oil and water or other contamination. If
compressed air is used which is not sufficiently purified, these contaminations can result in mal-
functions of the Purging unit or of the aspirating smoke detector. For example, the valve piston
system of the Purging unit can ice up or the measuring device of the aspirating smoke detector
can become oily, and therefore can become useless or can even be destroyed. This can also lead
to false alarms or increased contamination of the aspirating smoke detector as a result of particles
in the compressed air, which are again drawn in by the evaluation unit of the aspirating smoke
detector after a Purging process.
Metal shavings, other foreign particles or liquids in compressed-air lines must not get into the
Purging unit because otherwise the Purging unit can be damaged.
As recommended value for the purity of compressed air, Class 2 according to ISO8573-1:2010
should be used, which for oil permits a limit value of max. 0.1mg/m³ of compressed air. This
value also makes sense with regard to the durability of the compressed-air lines.
During the Purging process the Automatic Purging Units Series F-BO-AFE70 briefly need a very
large amount of air which is withdrawn from the compressed-air vessel of the compressed-air sup-
ply. The air output capacity of a compressor is only of secondary importance for the dimensioning
of the compressed-air supply of the Purging unit because usually the time between two Purging
processes is very long and therefore the compressor has sufficient time for charging the com-
pressed-air vessel. Therefore, only the dimensioning of the compressed-air vessel is dealt with
below.
Fig. 3:
Typical construction of a compressed-air system for providing the required compressed-air
volume of an Automatic Purging Unit Series F-BO-AFE70, and explanation of the terms used in
this chapter and by the calculation tool.
A ... Air vessel overpressure: This is the pressure that prevails in the compressed-air vessel – as
B ... Input overpressure: This is the pressure at the Purging unit's input (compressed-air connec-
C ... Pressure regulator (option): The pressure regulator SHOULD be used whenever the avail-
Tables 6 and 7 contain approximate values for the calculation of the minimum size of the com-
pressed-air vessel of the compressed-air system, depending on the air vessel overpressure and the
chosen input overpressure of the respective Purging unit. The result of the table is given in litres
per second of operation of the solenoid valve, and therefore it still has to be multiplied by the
well as the reference value that has been set on the compressor and at which the compressor
should turn itself on again.
tion) that results from the number and size of aspiration holes, from the flow rate of the
solenoid valve that has been installed in the Purging unit, as well as from the pressure
losses in the compressed-air supply pipe.
able air vessel overpressure is markedly higher than the recommended input overpressure,
and MUST be used whenever the air vessel overpressure is higher than the maximum input
overpressure of the F-BO-AFE70 used.
If several Purging units are supplied by the same compressed-air vessel, it is also possible
to use one pressure regulator for several Purging units. But in this case, please note the
maximum possible flow rate of the pressure regulator.
User Manual Series F-BO-AFE70
I56-4252-010
D200-104-00
Advertisement
Table of Contents
