Cleaver-Brooks CBH 40 - Flame Loss Sequence

Chapter 3-Sequence of Operation
main gas valves are simultaneously energized and
open, the normally open vent valve is also
energized and closes.
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 pi-
lot 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.
The cause for loss of flame or any other unusual
condition should be investigated and corrected be-
fore attempting to restart.
With the main flame established, terminal 11 is
powered (from terminal 10) transferring power to
the damper motor positioning switch and releasing
burner from low fire position subject to following
conditions:
With the damper positioning switch in the "low"
position, the circu-it to the damper mqtor is broken
and motor remains in a closed or low fire position.
With the switch in the "high" position, the damper
motor is powered directly and moves to an open or
high fire position.
With the switch in the "auto" position, power is
routed through the high-low fire control which
makes or breaks the circuit to the damper motor as
load demands.
On an oil fired unit, the opening of the damper
motor actuates switches which in turn energize the
intermediate and high fire solenoid valves increas-
ing the size of the fire to the high fire rate. Closing
of the motor de-energizes the high fire valves re-
ducing the flame to the low fire rate.
On a gas fired unit, the opening of the damper
motor actuates, through linkage, the disc in the
butterfly valve to allow a greater flow of gas, in-
creasing the size of the flame to high fire rate.
Closing of the motor decreases gas flow to a low
fire
rate.
BURNER SHUTDOWN
Dial at "Pos~ Purge"
The burner will fire until steam pressure or water
temperature in excess of demand is generated.
With the high-low fire control properly adjusted,
the damper motor should return to the low fire
position before the operating limit control opens.
When the limit control circuit is opened, the
following sequence occurs:
Relays lK, 3K and 4K drop out. The main fuel
valve(s) is de-energized and closes. Flame is ex-
3-6
tinguished and flame relay 2K drops out. The
blower motor continues to force air through the
boiler in a post-purge period. The timer begins
rotating.
Power is removed from terminal 11 breaking the
circuit to the damper motor. The motor returns to
the low fire position if it is not already in that
position.
At the end of the operating cycle, terminal 8 circuit
opens and de-energizes the blower motor. The
timer stops as it reaches its original position.
The control is now in readiness for subsequent re-
cycling and when steam pressure or water tem-
perature drops to close the contacts of the opera-
ting control the burner again goes through its nor-
mal starting and operating cycle.
E. flAME lOSS SEQUENCE
The CB-20 and CB-40 programmers recycle auto-
matically each time the operating control closes or
after a power failure. Both will lockout following a
safety shutdown caused by failure to ignite the
pilot, or the main flame, or by loss of flame. Lock-
out will also occur if flame or flame simulating
condition occurs during the pre-purge period.
Both controls will prevent start-up or ignition if
the pre-ignition or air flow interlocks open. The
CB-20 control will recycle in an attempt to correct
the shutdown situation (if it is self-correcting). The
CB-40 control will lockout upon any abnormal
condition affecting fuel or air supervisory controls.
The lockout switch must be manually reset follow-
ing a safety shutdown. A short cool down period is
necessary before the switch button can be de-
pressed and operation resumed.
The cause for loss of flame or any unusual condi-
tion should be investigated and corrected before
attempting to restart.
A. No pilot flame.
The pilot flame must be ignited and proven within
a 10 second period after the ignition cycle begins-
terminals 5 and 6 energized. The flame is proven
by the pull-in of relay 2K. If 2K is not energized
within this period, the fuel valve circuit (terminal
7) will not be powered and the fuel valve(s) will
not be energized. The ignition circuit is -immedi-
ately de-energized and the pilot valve closed. -
The blower motor will continue to operate. The
timer will stop after a short period of operation.
Approximately 30 seconds after the ignition circuit
is interrupted, the lockout switch (LS) will trip.
Master relay lK is de-energized. The flame failure
light and the alarm bell (optional) are energized.