Cleaver-Brooks CBH 40 - Page 34

Chapter 3-Sequence of Operation
The cause for loss of flame or any other unusual
condition should be investigated and corrected
before 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 circuit to the damper motor 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
the 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 valve reduc-
ing 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.
This is the end of the burner starting cycle. Timer
stops. Demand firing of boiler continues as re-
quired by load conditions.
BURNER SHI.HDOWN
Dial at "Post 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 operating limit control is opened the
following sequence occurs:
Relay 1K drops out. The main fuel valve(s) is de-
energized and closes. Flame is extinguished and
flame relay 2K drops out. The blower motor con-
tinues 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
3-4
timer stops as it reaches its original position.
The control is now in readiness for subsequent re-
cycling and when steam pressure or water temper-
ature drops to close the contacts of the operating
control the burner again goes through its normal
starting and operating cycle.
D. SEQUENCE Of' OPERATION-
Oil or Gas
Applicable to an optionally equipped boiler with
the CB-40 flame safeguard and program control
system.
The CB-40 control is used to comply with require-
ments of insurance underwriters such as Factory
Insurance Association (F.LA.) and the Factory
Mutual Engineering Association (FM) and certain
other codes. This programmer contains several in-
terlock circuits requiring the use of some or all of
the following devices in addition to those men-
tioned in Section B. Refer to the boiler wiring
diagram to determine the controls provided and to
follow this sequence.
High fire switch (HFS) (IRI)
Low oil pressure switch (LOPS)
100 and 200 series only
Low gas pressure switch (LGPS)
200 and 700 series only
High gas pressure switch (HGPS)
200 and 700 series only
This sequence covers burner operation from start-
up thru shutdown. No attempt is made to correlate
the action of the fuel supply system or feedwater
system except for those controls that directly affect
the action of the programming relay. Refer to the
wiring diagram supplied for this boiler in following
this sequence.
NOTE: The legend on the timer dial (Figure 1-3) in-
dicates the position of the timer and the
stage reached in the burner operating cycle.
The bar-graph shown in Figure 3-2, or on
the wiring diagram, indicates the sequence
of the various circuits. The technical
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: