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MACH® Series
Gas-Fired Boiler Installation
Page 26
Table 3-1 Combustion Reading For Setting Gas Safety Shut Off / Control Valves
Nominal High Fire Setting Low Fire Setting
Fuel
Gas Pressure % O
2
% CO
2
% O
2
% CO
2
Natural Gas
7" W.C 5.0 +
0.2 9.0 + 0.2 5.2 + 0.2 8.8 + 0.2
Propane
11" W.C 5.0 +
0.2 10.4 + 0.3 5.2 + 0.2 10.3 + 0.3
Adjustment:
There must be sufficient load to operate the boiler at
high fire to perform the following adjustments. Start
the boiler and observe proper operating parameters for
the system.
Note: The MACH C300 and C450 boilers are each
equipped with two gas safety shut off / control valves
that operate in parallel. When making any adjustment
to the valves, the adjustment must be performed on
each of the valves equally.
Example: If an increase in the gas flow is required to
lower the O
2
level, turn each of the maximum flow
restrictors equivalent amounts (i.e. ¼ or ½ turn each)
and allow the analyzer readings to respond and
stabilize before proceeding with additional adjustment.
Adequate response time must be allowed for
combustion readings to stabilize. This response time
will be longer for low firing rates than for high firing
rates.
High Fire Setting
Set boiler to the “Test Mode High”, as described
above, to achieve maximum firing rate of the boiler.
Check combustion readings using a combustion
analyzer. If combustion readings are not in
accordance with Table 3-1 adjust as follows:
Using a slotted screw driver or 2 mm hex wrench, set
the maximum restrictor (high fire screw – see the
figure below, item “D”) on each of the gas safety shut
off / control valves by turning clockwise or
counterclockwise to achieve the desired CO
2
or O
2
level; see Table 3-1 for correct settings. (There will be
a slight time delay between the adjustment and the
response of the CO
2
/O
2
measuring instrument).
Clockwise rotation decreases gas flow.
Counterclockwise rotation increases gas flow.
Low Fire Setting
Set boiler to the “Test Mode Low”, as described
above, to achieve minimum firing rate of the boiler.
Check combustion readings using a combustion
analyzer. If combustion readings are not in
accordance with Table 3-1 adjust as follows:
Using a 2 mm hex wrench, adjust the pressure
regulator offset adjustment (see the figure below, item
“R”) to achieve the CO
2
/O
2
level prescribed in Table
3-1. Note that equal adjustments must be made to
each of the valves. Adjustments to the offset pressure
regulators should not exceed ¼ turn at a time before
allowing the readings to respond and stabilize. Please
note, the rotation of the Low Fire adjustment is
opposite of the High Fire as follows: Clockwise
rotation increases gas flow, counterclockwise rotation
decreases gas flow.
"R"
"
D
"
C300/450 Adjusting Low and High Fire