Cleaver-Brooks CBH 40 - Page 35

PRE-PURGE PERIOD
Dial at Dot
When the burner switch is turned "on", power is
routed through the limit controls to terminals 3
and 4. Relay lK is energized. Power is also routed
to the blower motor starter.
Programmer terminal 13 is powered (from termi-
nal 10) to energize the damper motor which begins
driving the damper to the open or high fire posi-
tion. This allows a flow of purging air through the
boiler prior to ignition.
The timer will stop until the high fire switch (HFS)
i<: made. If proof of high fire position is not re-
t • .1ired, the timer will not stop but will continue its
cycle.
The running interlock circuit (to terminal 12) must
be completed within 10 seconds after the start of
timer rotation to energize relay 3K.
Continuity of the interlocks listed below allows the
sequence to continue.
In the event any of these are not closed at this
time, or if they subsequently open, relay 3K will be
de-energized. This will prevent the fuel valve cir-
cuit from being energized, or if occurring later into
the sequence, will de-energize this circuit. The
timer will complete its revolution to the starting
position and the programmer will lockout.
The blower motor starter interlock (BMSI) is
wired into the circuit to prove that the starter is
energized and to interrupt the circuit if the starter
should be de-energized for any reason.
The combustion air proving switch (CAPS) is ac-
tuated by air pressure from the forced draft fan to
prove the presence of combustion air.
When so equipped, the low oil pressure switch
(LOPS) must be closed to indicate that sufficient
fuel supply pressure exists.
Toward the end of the purging period, terminal 13
is de-energized to break the circuit to the damper
motor. The return spring in the motor brings it
back to a closed position and the damper to low
fire position.
Existing F.I.A. requirements and/or others require
additional pre-purge time beyond that normally
provided by the programmer. This is accomplished
through the use of a "purge extender" that is
plugged into the programmer. This device allows
the purging period to be extended by 30, 60 or 120
seconds depending upon the setting selected (refer
to program control bulletin for details).
IMPORT ANT: If the optional purge extender is
not used, the purge jumper provided with the re-
lay must be installed.
When the high fire switch closes, the purge ex-
tender is activated to provide the additional purge
Chapter 3-Sequence of Operation
time. The programmer timer is stopped and the
damper motor remains in high fire position until
this timing is completed. Upon completion, the
timer restarts and the damper motor returns to the
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 an interlock circuit to terminal
14. The timer will stop until the damper motor has
returned to the low fire position and the contacts
of the low fire switch are closed.
NOTE: The ignition trial cannot be started if for
any reason the flame relay pulls in during
the pre-purge. The timer will complete its
revolution and lockout at the start
position.
IGNITION PERIOD
Dial at "Pilot and Ignition"
A. Spark Ignited Oil Fired Burner
The ignition transformer is energized from termi-
nal 5. The low fire solenoid valve is energized from
terminal 6 which in this case is jumpered to termi-
nal 7. With combustion air, ignition spark and oil
present the low fire flame is ignited. When flame is
detected, flame relay 2K is energized.
B. Gas Pilot Ignited Oil or Gas Fired Burner
The ignition transformer and the gas pilot solenoid
valve are energized from terminal 5. With combus-
tion air, ignition spark and gas present the pilot
flame is established. When flame is detected, flame
relay 2K is energized.
The pilot flame must be established and proven
within a 10 second period in order for the ignition
cycle to continue. If for any reason this has not
happened, the system will shut down and safety
lockout will occur.
The cause for loss of flame or any other unusual
condition should be investigated and corrected be-
fore attempting to restart.
Dial at "Main Burru~r"
A. Spark Ignited Burner
Terminal 7 is now powered. The main fuel valve
(LFOV), already opened, will continue to be ener-
gized from this terminal when terminal 6 is de-
energized at the end of the main flame proving
period.
B. Gas Pilot Ignited Burner
Main gas valve(s) (gas fired unit) or the low fire
solenoid valve (oil fired unit) is energized from ter-
minal 7. Main flame is ignited.
F.I.A. regulations, or others, require two main gas
valves with a vent valve between them. As the
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