Cleaver-Brooks CBH 40 - Page 33

sequence of the various circuits. The techni-
cal bulletin for this control contains a
schematic wiring diagram that details the
timing sequence of the various programmer
contacts. The following description refers to
the dial indication and not to the timing,
since the timer is interrupted and governed
by other components during a normal cycle.
On a combination fuel unit, the gas/oil switch must
be set for the proper fuel.
With the programmer energized and with all other
operating conditions satisfied, the following pro-
gramming sequence occurs:
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 1K 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 running interlock circuit to terminal 12 must
be completed within 10 seconds after the start of
timer rotation.
Continuity of the interlocks listed below complete
this circuit which allows the sequence to continue.
In the event any of these are not closed at this
time, or if they subsequently open, relay lK will be
de-energized. The timer will complete its revolu-
tion to the starting position and the programmer
will recycle.
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 actu-
ated by air pressure from the forced draft fan to
prove the presence of combustion air. This switch
is not normally supplied on a 100 series boiler.
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 dosed position and the damper to 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: A burner start cannot be made if the
Chapter 3-Sequence of Operation
flame relay holds in for any reason. If, af-
ter the first 15 seconds of pre-purge, the
flame relay should pull in for any reason
the ignition cycle cannot be started. In-
stead, the timer will complete its revolu-
tion and attempt to recycle or lockout.
IGNITION PERIOD
Dial
at "Pilot and Ignition"
A. Spark Ignited Oil Fired Burner (100 Series)
The ignition transformer is energized from termi-
nal 5. The low fire solenoid valves are energized
from terminal 6, which in this case is jumpered to
terminal 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 (200
and 700 Series)
The ignition transformer and the gas pilot solenoid
valve are energized from terminal 5. With com-
bustion air, ignition spark and gas present the pilot
flame is established. When flam~ 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 Burner"
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 valves (oil fired unit) is energized from
terminal 7. Main flame is ignited.
After a 10 second trial period for the proving of
main flame, power is removed from terminal 5 de-
energizing the ignition transformer and the gas
pilot valve. The gas pilot flame is extinguished.
If for any reason main flame does not light or stay
lit, relay 2K will drop out causing the fuel valve(s)
to close. The safety switch will trip to lockout the
control. Refer to flame loss sequence section for
description of action.
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