CHAPTER3
to its full open
or
high fire position. This allows
a flow
of
purging air through the boiler prior to
the ignition cycle.
On certain boilers the circuitry will include a high
fire switch
(HFS).
The
purpose
of
this switch is
to prove that the modulating damper motor
(MOM) has driven the damper to the open posi-
tion during the pre-purge cycle. In this instance,
the "high fire proving circuit"
is
utilized.
The controls wired into the "running. interlock
circuit" must be closed within
10 seconds after
the start sequence.
In the event any
of
these
controls are not closed at this time,
or
if
they
subsequently open, the program relay will go into
a safety shutdown.
At
the completion
ofthe
high flre purge period,
the program relay signals the modulating damper
motor (MDM)
to
drive the air damper to its low
fire position.
To assure that the system
is
in
low fire position
prior to ignition, the low fire switch
(LFS) must
be
closed to complete the
"low
fire proving cir
..
cui t." The sequence will stop and hold until the
modulating damper motor (MDM) has returned
to
the low fire position and the contacts
of
the
low fire switch
(LFS) are closed. Once the low
fire switch
is
closed, the sequence
is
allowed to
continue.
NOTE:
The
ignition
trial
cannot
be
started
if
flame
or
a
flame
simulating condition is sensed
during the pre-purge period. A
safety shutdown will occur
if
the
flame
is
sensed at this time.
Ignition
Cycle -
The
ignition transformer (IT)
and gas pilot valve (GPV) are energized from the
appropriate pilot ignition
terminal.
NOTE:
An
oil-fired
burner
may
be
equipped with an oil pilot rather
than a gas pilot
..
The ignition
se-
quence
of
both is identical.
CHAPTER
3--8
SEQUENCE
OF
OPERATION
The pilot flame must be established and proven
by
the flame detector (FD) within a 10 second
period in order for the ignition cycle to continue.
If
for any reason this does not happen, the system
will shut down and safety lockout will occur.
NOTE:
Depending
upon
the
require-
ments
of
the regulatory body, in-
surer
or
fuel being burned, either
the
10
or
15 second pilot ignition
terminal may be used. Both
pro-
vide the same function but differ
in
the time interval allowed for
proving
main
flame
ignition.
Refer
to
the
boiler
wiring
diagram.
With a proven pilot, the main fuel valve(s)
(OV
or MGV)
is
energized and the main fuel valve
light (FVL)
in the panel
is
lighted. The main
flame
is
ignited and the trial period for proving
the main flame begins. It lasts
10 seconds for
light oil and natural gas, and 15 seconds for heavy
oil. At the end
of
the proving period, if the flame
detector still detects main flame, the ignition
transformer and pilot valve are de-energized and
the pilot flame
is
extinguished.
NOTE:
If
the main flame does not light,
or
stay lit, the fuel valve will
close. The safety switch will trip
to lockout the control. Refer to
flame loss sequence section for
description
of
action.
!WARNING
The cause
for
loss
of
flame
or
any
other
unusual
condition
should
be
Investigated
and
cor-
rected before
attempting
to
res-
tart. Failure
to
do
so may
result
In
serious
personal
Injury
or
death.
Run
Cycle-
With main flame established, the
program relay releases the modulating damper
motor (MDM) from
its low fire position to con-
trol by either the manual flame control (14FC)
or
75()..150
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