Laars Mighty Max VW Series, Installation, Operation And Maintenance Instructions

Page: 21 / 32

Mighty Max Volume Water Heater
Page 21
c. Gas Orifice Differential Pressure
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 11, the correct
input rate and gas to air ratio is achieved.
3F-3. Venturi Setup Procedure
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 11, “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.
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 11. Venturi Pressure Settings.
3. Measure the gas offset pressure. Using the
regulator only, adjust the gas offset pressure
according to the installation’s altitude in Table 11
(+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 11,
adjust the regulator as needed.
5. Measure the gas orifice differential pressure.
This pressure must be adjusted according to
Table 11 (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 11.
7. After setting all pressures, turn the heater off and
replace each shutoff valve with the factory
installed threaded plugs. The venturi has now
been adjusted for proper operation.
SECTION 4
Maintenance
4A. General Instructions
1. Oil the water circulating pump in accordance
with the manufacturer's instructions.
2. Oil the blower motor bearings every 6 months.
Figure 17. Gas Orifice Differential Pressure.
4.0" WC