18
Maxitrol 14
Amplifier
High Temperature Limit
airflow switch to close. The high airflow switch protects against profile plate failures that cause excessive
airflow through the burner. In the event that the pressure drop across the burner is not in the range of the
airflow switch, gas flow to the burner is stopped by the Flame Safety Control.
The graphs below illustrate the approximate cfm going through the unit vs. the differential pressure
measured by the airflow switch. Simply measure the differential profile pressure drop at the airflow tubes
in the unit and match that value up to the matching unit curve below. This will show the cfms traveling
through the burner and will indicate proper airflow or airflow problems (too much or not enough). If the
pressure drop is outside of the .15” to .80” range, the blower rpm should be adjusted to fix airflow.
Size 1-3 Heater CFM vs. Burner Profile Pressure
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
Burner Differential Profile Pressure (in. w.c.)
C
F
M
Size 1
Size 2
Size 3
Size 4-5 Heater CFM vs. Burner Profile Pressure
3000
5000
7000
9000
11000
13000
15000
17000
19000
21000
23000
25000
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
Burner Differential Profile Pressure (in. w.c.)
C
F
M
Size 4
Size 5
Modulating Gas System
The second system, the modulating gas system, consists of a temperature
selector dial, a discharge air sensor, an amplifier, and a modulating gas valve.
The two types of modulating gas systems used are the Maxitrol 14 or RTC
Solutions controls and the Maxitrol 44 series. The Maxitrol 14/RTC utilizes a
discharge air sensor and modulates the Maxitrol gas valve to provide discharge
air to match the selected temperature on the temperature selector. The Maxitrol
44 utilizes a room temperature sensor to control room temperature as well as a
discharge air sensor in order to control the discharge air temperature. The
modulating gas valve controls the amount of gas flow to the burner based on
the temperature rise needed. When the modulating gas valve is all the way
open and achieving the maximum BTUs and temperature rise of the unit, it is
called “high fire”.
High Temperature Limit
One of the backup safety devices is the
high temperature limit switch.
This switch is a mechanical thermostat that measures the temperature
inside the unit downstream of the burner. If the factory-set temperature
of 170°F is exceeded, it will signal the FSC to turn off the burner. This
requires a manual reset of the high temperature limit. This insures that
the discharge does not exceed 185°F.
Operation Summary
With the blower already running and the airflow switch proven;
The outside air temperature falls below the setting of intake air thermostat
or
The optional remote panel is set to “Manual” and “Heat” mode
•
The FSC in energized and the following occurs;
FSC indicates that it has power by illuminating the OPR CTRL LED
Summary of Contents for Modular Direct Fired Heaters
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