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PFU 780 · Edition 02.12
38
4 .7 Air valve control PFU . .L
Parameter 30, Behaviour of the air valve during operation
Parameter 31, Behaviour of the air valve during start-up
Parameter 32, Behaviour of the air valve in the event of a
fault lock-out
The PFU..L features an adjustable air valve control. The display
shows that purging is currently being carried out with
P 0
.
A
indicates that the air valve is being activated for cooling
or heating.
The PFU..L supports the following functions:
–
Purge
– Cooling in start-up position/standby
– Switching of the burner between low and high burner out-
put during operation via the air valve
– To start up the burner as intended, external activation of
the air valve can be blocked during start-up (prevents
synchronisation problems between the PFU and the cen-
tral control system)
– Controlling the air valve so that it
– opens with valve V2,
– opens once the main burner has reached its operating
position
– Low fire over run time t
KN
after a normal shut-down
4 .7 .1 Purge
Parameter 42 = 0: The air valve is closed when voltage is
applied to terminal 30e.
Parameter 42 = 1: The air valve is opened when voltage is
applied to terminal 30e.
In the case of multiple burner applications, burners with me-
chanical combustion air supply are used. The air for combus-
tion and pre-purge is supplied by a central fan controlled by
a separate logic. This logic determines the purging time.
The PFU..L supports centrally-controlled pre-purge or post-
purge. The PFU..L is informed that purging is currently being
performed by input 30e. It then opens the air valve, regard-
less of the status of the other inputs (purging has priority). The
display indicates
P 0
.
PFU 780..K2: For purging, the safety interlock (limits) must
activate input 26e and input 30e of the PFU.
4 .7 .2 Cooling in start-up position/standby
The air valve can be activated externally via input 10a for cool-
ing in the start-up position. During activation of the air valve
the display shows
A 0
, indicating that cooling is currently
being carried out.
4 .7 .3 Burner start
Parameters 30 and 31 determine the behaviour of the air valve
during burner start.
Parameters