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5 Functional Description with Process Diagrams
5.2.6.3 Functional Description
The gas valve leakage test checks the integrity of main gas valves 1 & 2. The supply gas pres-
sure is used to carry out this automatic test procedure. After a controlled burner shutdown,
any gas in test line (the space within the pipework between the two main gas valves) will have
been burnt off and so the pressure in the test section should be atmospheric i.e. gas pressure
> min = 0.
The CMS checks this and if true then Main gas valve 1 is opened for a short time to allow gas
to flow into the test line.
The CMS checks that the gas pressure > min value changes to = 1. This pressure condition
must remain for 30 seconds after which the gas valve leakage test is deemed successful and
complete.
If the valve leakage test line is not empty at the start (e.g. as a result of a previous fault shut-
down), main gas valve 2 opens first. The valve leakage test line is vented (into the combustion
chamber or over the roof, depending on the system; for suggested circuit, see Appendix). It is
checked, whether the line remains pressureless for 30 seconds. Otherwise the procedure is,
as described previously.
The valve leakage test is performed before ignition.
The pressure monitor for the valve leakage test line must be connected to ’Gas pressure >min’
input (terminal 47). This also monitors the minimum gas pressure during normal operation. If
there is a requirement for another minimum pressure device to be monitored during normal
operation then this should be incorporated into gas safety interlock for this purpose.
However, the test line must be designed to ensure that the test time of 30 seconds per valve
is sufficient for reliable detection of a 0.1% leak of the fuel gas consumed at maximum com-
bustion heat output, but at least 50 dm
3
/h.
NOTICE
Respect the national safety regulations and standards.
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