9.12 Post Purge
Figure 9.12.i Post Purge
The Post-Purge phase is shown in Figure 9.12.i. When T53 is switched off to turn the burner off, the Flame Safeguard
controller will close the fuel valves and take back control of the servo. If a post purge is set, it will drive the servo to
open, purging fresh air through the burner/boiler, when the burner shuts down in normal conditions. The outputs of
the main gas valves 1 and 2, and the pilot valve are switched off (closed). See option/parameters 118 and 135.
The post purge timer begins once the motor has moved to their post purge positions and the purge interlock has
been made on terminal 81. This does not apply to NFPA post purge.
After Post-Purge, the MM will go back to the Recycle phase and the burner start-up sequence will commence as
required.
Note: If NFPA Post-Purge is selected, then the burner will also perform a Post-Purge in the event of a lockout/error
at any time after the Ignition phase, and the purge interlock on terminal 81 is not checked.
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