LAARS Mighty Max HH (Sizes 320M - 400M) - Installation, Operation and Maintenance Instructions - Manual (Page 21)

Mighty Max Hydronic Boiler Page 21
and the venturi pressure switch tubes are in place and
firmly connected.
The field checkout involves measuring gas and
venturi pressures, and observing the flame through the
sight glass. If necessary, the gas input rate can be
measured by timing the gas meter.
Install shutoff valves at the gas orifice (regulator
outlet) tap (red), at the venturi inlet tap and at the gas
plenum tap. Do not remove any of the plastic fittings
or plastic tubing. After installing the shutoff valves, be
certain they are closed.
a. Unfired Venturi Differential Pressure -
Natural Gas
NOTE: Turn off the main manual gas valve.
The difference in pressure between the venturi
inlet tap and the gas plenum tap (see Figure 15). This
measurement is taken by connecting the positive side
of the manometer to the venturi inlet tap and
connecting the negative side of the manometer to the
gas plenum tap. This measurement is taken with the
boiler not firing. It is a temporary setting used to start
the boiler and check for air flow problems.
b. Gas Offset Pressure - Natural Gas
The difference in pressure between the venturi
inlet tap and the outlet of the gas regulator (see
Figure 16). This measurement is taken by connecting
the positive side of the manometer to the venturi inlet
tap and connecting the negative side of the manometer
to the gas orifice tap. This measurement is an
indication of the gas to air ratio and must be
performed while the unit is firing.
c. Gas Orifice Differential Pressure -
Natural Gas
This measurement is the pressure drop across the
gas orifice. This measurement is taken by connecting
the positive side of the manometer to the gas orifice
tap and the negative side of the manometer to the gas
plenum tap (see Figure 17). This measurement in
conjunction with the gas orifice size is an indication of
the gas firing rate and must be performed while the
unit is firing.
By setting the gas offset pressure and gas orifice
differential pressure according to Table 10, the correct
input rate and gas to air ratio is achieved.
GAS GAS ORIFICE UNFIRED
ELEVATION, OFFSET DIFFERENTIAL VENTURI
FT PRESSURE PRESSURE DIFFERENTIAL
inch W.C. inch W.C. inch W.C.
SEA LEVEL +0.4 +4.0 +5.8
2000 +0.4 +3.7 +5.3
4000 +0.4 +3.4 +4.9
6000 +0.4 +3.2 +4.6
8000 +0.4 +2.9 +4.2
10000 +0.4 +2.7 +3.9
Table 10. Venturi Pressure Settings - Natural Gas.
3.6.3 Venturi Setup Procedure -
Natural Gas
1. Loosen the nut on the blower shutter to allow for
adjustment. Turn the heater on so that the blower
is running and the heater is not firing. Measure
the unfired venturi differential pressure. In this
unfired condition, adjust the shutter until the
unfired venturi differential pressure is according
to Table 10, “Unfired Venturi Differential” (5.8
± .3 inches wc at sea level). If this pressure range
can not be achieved, check for blockage in the
combustion air inlet, boiler and venting system.
If there is no obvious cause contact a qualified
Laars service technician.
2. Approximately 40 seconds after the blower starts
the gas valves will open. The heater is now
firing. If the heater is not running, check all
manual gas valves and heater safety devices.
Ensure proper gas supply pressures according to
Table 4 in Section 2.
3. Measure the gas offset pressure. Using the
regulator only, adjust the gas offset pressure
according to the installation’s altitude in Table 10
(+0.4 inches wc. at sea level). REPLACE THE
REGULATOR CAP BEFORE TAKING GAS
PRESSURE READINGS. Turn the regulator
screw clockwise to decrease the gas offset
pressure, turn the regulator screw
counterclockwise to increase the offset.
4. Using the toggle switch, turn the heater off. Turn
the heater back on and check the gas offset
pressure while the heater is firing. If the gas
offset pressure is not according to Table 10,
adjust the regulator as needed.
5. Measure the gas orifice differential pressure.
This pressure must be adjusted according to
Table 10 (4.0 ± .2 inches wc at sea level). Use
the blower shutter to adjust the gas orifice
differential.
6. By adjusting the gas orifice differential, the gas
offset pressure will change. Therefore you must
repeat steps 3-5 until the gas offset and gas
orifice differential pressures are according to
Table 10.
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