CHAPTERS
Through the manual flame control switch, posi-
tion the cam so that the adjusting screw adjacent
to the end
or
high fire screw contacts the cam
follower. Perform a combustion analysis at this
point.
If
an adjustment
is
necessary, tum the
adjustment screw accordingly
to increase
or
decrease the fuel flow. Take a combustion read
..
ing to verify the input. Repeat as necessary until
the desired flow
is obtained. Repeat this process,
stopping at each adjusting
screw,
until the low
fire adjusting screw
is
reached.
CAUTION!
Do
not
use
any
lubricant
on
the
adjusting
setscrews.
These
have a
nylon
locking
Insert
In-
tended
to
provide
locking
torque
and
resistance
to
loosening
and
could
damage
·equipment.
Standard Burner
Low
Fire Adjustment
With the low fire cam screw, the fuel input should
be
adjusted to approximately
25%
of
that at high
fire (Table 3). At low frre the
C02
flue gas
content should be
8.8-9.1% with 4-4.5%
02.
It
may be necessary to readjust the setting
of
the
low fire stop screw in order to obtain the proper
air/fuel ratio at the low fire rate. To ensure that
the low fire position
of
the gas butterfly valve
is
always the same, allow one tum
of
the stop screw
for overtravel.
If
the air damper needs to be adjusted in order to
provide the correct low fire air/fuel ratio,
com-
bustion must be rechecked at higher firing rates
and adjusted as required.
If
all cam screws are properly adjusted, none will
deviate from the general overall contour
of
the
cam face.
750-150
ADJUSTMENT
PROCEDURES
High Turndown Burner
Low
Fire Adjustment
With the low fire cam screw, gas flow should be
adjusted
to obtain a minimum fuel input 10%
of
that at high frre (Table 4). The resulting flue gas
COz
content should be
5.8-6.
7% with a cor-
responding
02
content
of
11-9.5%.
It
may
be
necessary to readjust the setting
of
the
low fire stop screw in order
to obtain the proper
air/fuel ratio at low fire. To ensure that the low
fire position
of
the gas butterfly valve
is
always
the same, allow a half tum
of
the stop screw for
overtravel.
H the air damper must be reset
to
meet the low
fire air/fuel requirements, combustion at higher
firing rates must be rechecked.
The second cam adjusting screw may need
to
be
adjusted
in
order to maintain a smooth cam
profile.
If
all screws are properly adjusted, none
will deviate from the general overall contour
of
the cam Jace.
R.
LOW GAS
PRESSURE
SWITCH
Adjust the scale setting to slightly below the
normal burning pressure. The control circuit
will
be
broken when the pressure falls below this
point.
Since gas line distribution pressure may
decrease under some conditions, shutdowns may
result
if
the setting
is
too close to nonnal. How-
ever, regulations
reqqire that the setting may not
be
less
than
50%
of
the
rated
pressure
downstream
of
the regulator.
Manual resetting
is
necessary after a pressure
drop.
Press the reset lever after the pressure
is
restored.
Make
sure
that a mercury switch
equipped control
is
level.
CHAPTER 5-17
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