PFU 780 · Edition 02.12
43
4 .7 .8 Low fire over run time t
KN
after a normal shut-down
00
A8
t
t
KN
22e
26a
16c
18e
2c–4c
18a
14a
88
10e
26e
30a
28c
2e–4e
6a–6e
V1
1
V2
2
ϑ
1
ϑ
2
2
1
VR..R
PFU 780..L
A
P
L1
1
2
SPS
PLC
CPE
VAS 1
VG..N
GIK..B
1
2
ϑ
TZI
Parameter 36
Settings: 0; 3; 5; 10; 15; 25 or 60 (low fire over run time in
seconds)
This parameter is applicable to systems with a pneumatic link
between gas and air and On/Off control.
Parameter 36 = 0 (low fire over run time t
KN
= 0 s):
Without low fire over run, the gas side is closed immediately
owing to the quick-closing gas valve in the case of On/Off
control. The air side closes more slowly. The air flowing in
during the closing time increases the O
2
content in the com-
bustion chamber.
Parameter 36 = 3; 5; 10; 15; 25 or 60 (low fire over run time
t
KN
= 3, 5, 10, 15, 25 or 60 s):
The air valve closes slowly after the activation signal has
been switched off. The gas valve remains open for t
KN
. This
means that the burner, after deactivation of the main burner
start-up signal (
ϑ
2), is initially adjusted down to low fire and
then switched off completely.
Using the low fire over run function reduces the O
2
content in
the furnace atmosphere.
Flame control is still operational. Can be used only in the case
of pneumatic link and On/Off control. It must be ensured that
no excess gas occurs.
The low fire over run time has an effect on the behaviour of
the main burner only.
Background: The pilot burner is only used in single-stage
operation.
Parameters > Air valve control PFU . .L