FloAire Compact Direct Fired Heater - Manual (Page 18)

18
Maxitrol 14
Amplifier
Air Flow Switch
Air Flow Switch
There are both high and low airflow switches contained within one housing
measuring the pressure drop across the burner. This is to insure that there is
proper airflow (.15 in. w.c. to .80 in. w.c.) across the burner and proper
combustion at all times. Both switches are wired in series and have single pole
double throw (one common contact, one normally open contact, and one normally
closed contact) switches that are ‘switched’ by air pressure. There are two airflow
tubes in the heater, located near the burner and profile plate assembly (profile
plates surround the burner and control air into the burner section). In the case of
clogged filters, blocked intake, excessive duct static pressure, or a broken belt, the
correct burner differential pressure may not be achieved, not allowing the low
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.
76 Profile Chart
400
600
800
1000
1200
1400
1600
1800
0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8
Burner Differential Profile Pressure (in. w.c.)
C
F
M
Modulating Gas System
The second system, the Maxitrol modulating gas system, consists of a temperature
selector dial, a discharge air sensor, an amplifier, and a modulating gas valve. The two
types of Maxitrol systems used are the Maxitrol 14 series or the Maxitrol 44 series. The
Maxitrol 14 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”.