LAARS Mighty Max HH (Sizes 320M - 400M) - Installation, Operation and Maintenance Instructions - Manual (Page 20)

Page 20
LAARS Heating Systems
• Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
If you don't smell gas, go to the next step.
7. Turn on manual gas valves.
8. Rest all safety devices (manual resets on high
limit, low water cutoff, etc.).
9. Replace control access panel.
10. Turn on all electric power to the boiler.
11. Set thermostat to desired setting.
12. If the boiler will not operate, follow the
instructions to turn off gas to boiler and call your
service technician or gas supplier.
a. Turn off main electrical switch.
b. Close all manual gas valves.
3.4.1 Setting Temperature Controls
The temperature control differential is factory
set at 15°F. This setting can be adjusted from 1 to
30°F to suit your application. Adjustment is made by
taking the cover off the temperature controller and
turning the potentiometer marked “DIFF”, which is
located just below and to the left of the controller’s
setpoint dial.
To set the temperature and high-limit controls:
a. Set the temperature controller at the system
design temperature.
b. For boilers with the temperature controller bulb
at the boiler inlet, set the high-limit 40°F to 50°F
above temperature controller setting.
c. For boilers with the temperature controller bulb
at the boiler outlet, set the high-limit 15°F to
25°F above temperature controller setting.
3.5 To Shut Down System
To shut down the boiler, turn off all manual gas
valves and electrical disconnect switch.
NOTE: There is a filter which needs to be cleaned
prior to setting pressures. See Section 4.4.2 “Filter
Service” before proceeding.
3.6 Venturi Adjustment - Natural Gas
Verifying proper operation of the combustion
flow system has two aspects - air flow and gas flow.
Air flow is checked by measuring pressures at service
taps on the venturi. Gas flow is checked by evaluating
venturi pressures and the regulator offset pressure.
In a venturi flow system the difference between
various pressures is far more important than their
“gauge” value relative to the room. The gas pressure
offset and the gas orifice pressure differential are
especially important concepts. The following section
describes this setup procedure.
3.6.1 Pressure Measurement Ports -
Natural Gas
Air flow enters the venturi through the filter box
and blower assembly. It is pushed through a
converging section and into the throat, where pressure
is reduced substantially. Gas flow is pulled into the
throat through an orifice. The orifice is located
between the throat and the regulator. Air and gas are
combined in the throat and mix thoroughly as they
proceed through the venturi tailpipe to the burner.
Service taps are provided at three places. One is
located on the chamber with the gas connection, this
tap is called the gas plenum tap. The other is located
above the gas plenum tap, this port is called the
venturi inlet tap. The third tap, gas orifice tap, is
located on the red orifice holder directly before the gas
connects to the venturi. These taps have service plugs
in them. Do not remove any of the plastic fittings or
plastic tubing. To evaluate system operation requires
accurate measurement at these taps. An inclined
manometer with a zero to 6 inches water column range
is ideal. Other instruments may be used, but the
“positive/negative” nature of the readings must be
well understood. Gas pressure offset measurements are
at very low levels (0.4" WC), the instrumentation must
be capable of determining it accurately (see Figure 15,
16 and 17).
3.6.2 Adjustment Procedure - Natural Gas
Note that an equalizer tube is connected from a
port on the side of the venturi inlet to the port of the
regulator. This is a very important component which
allows the regulator to track air pressure even when
abnormal conditions occur, such as blockage of the
combustion air. Before firing, confirm that this tube
Overall
Operation
Figure 14. Typical Venturi System.
Air
Equalizer
Tube
Negative
Pressure Regulator
Gas
Gas
Orifice
Air/Gas
Mixture
OUT OF
PRODUCTION