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T-Product · BCU 465 · 2006 April
Air Valve Control of BCU 465
Purging
If the purge function is required, the
user must supply an approved ex-
ternal timer. The individual air valves
can be energized through the BCU
for purging if the system is frequency
fired. Therefore apply voltage to ter-
minal #22. If the combustion sys-
tem has a proportionally controlled
air valve the air valve will need to be
controlled externally.
Air Valve Control
The operation of the air valve output
is determined by the setting of pa-
rameters 30, 31 and 32 and 37 to 41
(see Table Parameter Setting).
When the air valve output terminal
#26 is energized, the dry contact
#50/#51 is closed.
Pre-purge
Parameter 37 (pre-purge at start-
up):
Parameter #37 can be used to
clear the chamber of explosive
gases. Selecting a time between 0
seconds and 250 seconds will open
the air valve simultaneously with the
start signal terminal #4. After the
air valve closed, then trial for ignition
will begin.
BCU program-controlled air
valve function
Parameter 30 =
0: No program control
1: Air valve opens with V1
2: Air valve opens with V2
Additional feature for programmed
air valve control: Low fire delay time;
parameter 36:
If the gas is controlled with an air/fuel
ratio regulator cross-connected to
the burner air supply piping, this time
may be factory set up to 25 seconds
on demand.
This ensures the burner is at low fire
before switching off when operating
in an off-low-high-low-off control
system.
Caution:
Use only with cross-con-
nected ratio regulator! Gas valve
remains opened while air valve is
shutdown! However, flame super-
vision is active.
If the flame fails
during this time, a safety shut
down without fault lockout will
occur.
Post-purge
Parameter 38 (post-purge after regu-
lar shut-down):
Selecting a time between 0 seconds
and 3 seconds allows the air valve to
open after normal shutdown.
Parameter 39 (pre-purge after safety
shut-down):
Selecting a time between 0 seconds
and 250 seconds will open the air
valve in the event of a safety or limit
failure. If terminal #4 remains ener-
gized and the limit failure is corrected,
the air valve will open for the selected
time period and then the minimum
off-time runs, before burner restarts.
However, this is disabled when auto
ignition flame management bypass
is active.
Post purge time may be activated
individually: Before a recycle attempt
is made (parameter 40) and after a
manual reset (parameter 41). To en-
able a recycle attempt, set parameter
12 to “1”.
Operation
