Cleaver-Brooks CBH 40 - Page 41

fire position. There possibly may be air trapped in
the high fire oil lines and it may be necessary to
operate the burner for several cycles to assure that
these lines become filled with oiL Failure of oil to
flow through the high fire nozzles promptly may
cause the increased combustion air to extinguish
the low fire flame.
After
the unit is thoroughly warmed a combustion
analysis test should be made with instruments and
fuel flow and/or air flow regulated as required.
Refer to adjustment procedures in Chapter 5. To
properly perform this test and adjustment it is
necessary that burner be allowed to fire at maxi-
mum rate sufficiently long enough to achieve
desired results.
Refer to Section E of this chapter for normal firing
operating and shutdown sequences.
CAUTION: It is advisable to check for tight shut-
off ol" fuel valves. Review Chapter 5.
D. GAS BURNER STARTsUP
(200 and 700 Series)
PREPARATION FOR INITIAL FIRING
Close main gas cock and open pilot gas cock.
On a 200 series boiler, set the gas-oil selector
switch to "gas". Although not mandatory, it is sug-
gested that oil pump belt be removed during
periods of extended gas firing.
Check
the linkage attached to the butterfly valve
to insure that it has free movement and that all
connections and set screws are tight. The linkage
was set at the factory but if adjustment is required
see Chapter 5.
Verify the presence and availability of gas. On a
new
installation, a representative of the gas utility
should be present when gas is first turned into the
system to supervise purging of the new gas line
unless this has already been done.
Determine that sufficient gas pressure exists at the
entrance to the gas train. This can be noted by in-
stalling a gas pressure test gauge in the line. Refer
to Chapter 5 for information on pressures and flow
rates.
Check that damper positioning switch is set to
"low". Turn burner switch to "on". The blower
motor will start and the programming control
timer will begin rotating.
The damper will open for the pre-purge period and
allow a flow of air through the fireside area of the
pressure vessel. The damper motor will return to
the low fire position after this pre-purge period is
completed. The low fire switch must be closed for
action to continue.
Now check for ignition spark and gas pilot. When
the legend "pilot ignition" appears in the timer
Chapter 4-Starting and Operating Instructions
dial, the ignition transformer and gas pilot valve
are energized. The gas pilot flame may be viewed
through the sight glass on the rear door.
The main burner will not light since the main gas
shut-off cock is closed. When the timer dial indi-
cates "main burner" determine that the main gas
valve opens when energized. In the case of a dia-
phragm valve, the click of its solenoid will indicate
that it is energized. The valve will not actually
open since there is no gas pressure available. Dur-
ing normal operation the position of the
diaphragm valve may be determined by observing
the flag in the window on top of the valve which
shows
black when the valve is closed and yellow
when opened. In the case of a motorized valve,
yellow showing on the stem indicates that the
valve is closed. ·
As soon as valve action is confirmed, turn the bur-
ner switch off and let programmer finish its cycle.
Check
to see that the gas valve has closed.
With evidence of a good pilot and operating main
gas valve, unit is ready to be fired. Reset the safety
switch in the event programmer locked out prior to
the burner switch being turned off.
Review
of the sequence of operation given in Chap-
ter 3 for a complete description of the action that
takes place during a starting and operating cycle.
INITIAL START-UP AND FIRING
Set damper positioning switch to "low". Turn the
burner switch "on" and when the timer dial indi-
cates "main burner", slowly open the main gas
cock. Main flame should ignite unless there is air
present in the line. In this event, turn the burner
switch "off' and allow programmer to run through
its normal shutdown cycle. Several efforts may be
necessary to "bleed" air from the line.
On
an ignition failure, the blower will continue
running to purge the burner of any unburned fuel
vapors before stopping. After ignition failure wait
a few moments before resetting the safety switch.
CAUTION: The burner and control system is de-
signed to provide a pre-purge period
of fan operation prior to establishing
ignition spark and pilot flame. Do not
attempt to alter the system in any way
that might Circumvent this feature.
When main flame is established observe that it is
extinguished promptly when burner is shut down.
Burner will normally continue to burn for a second
or two after shutdown due to the gas remaining
downstream of the cut-off valve. If flame continues
to burn for a longer period, or during blower motor
spin down, immediately turn burner switch "off'
and close main gas cock. Investigate and correct
the cause of valve leakage before re-lighting the
burner. The main gas valve is tight seating
provided nothing prevents tight closure. Foreign
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