MACH® Series
Gas-Fired Boiler
Installation
Page 25
Table 3-1 Combustion Reading For Setting Gas Safety Shut Off / Control Valves
Nominal
High Fire Setting
Low Fire Setting
Model
Fuel
Gas Pressure
% O
2
% CO
2
% O
2
% CO
2
300
Natural Gas
7" W.C.
4.9+ 0.2
9.1+ 0.2
5.1+ 0.2
8.9+ 0.2
450
Natural Gas
7" W.C
5.0+ 0.2
9.0+ 0.2
5.2+ 0.2
8.8+ 0.2
300
Propane
11" W.C
4.9+ 0.2
10.5+ 0.3
5.1+ 0.2
10.3+ 0.3
450
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® Series boilers are 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.
