AAON RL-240 - Manual (Page 53)

53
Figure 34 - Typical Factory Mutual (FM) Gas Piping Schematic for a Direct Fired Heater
The burner comes with a pilot to ignite the
flame and the pilot includes an adjustable
orifice. An ignition transformer and spark
igniter provide the spark to ignite the pilot
and the pilot lights the main burner. The
pilot and main burner flames are verified
with a flame rod or UV flame supervisor.
Capacity is controlled by a modulating gas
valve.
Ignition Sequence of Operations:
1. Pre-purge of the burner with fresh air for
30 seconds. Ignition will not proceed if
flame is detected.
2. Pre-ignition of the sparker for 2 seconds
in air only
3. Open the pilot gas valve for 10 seconds
and verify pilot flame detection. Safety
shutdown occurs if pilot is not detected
by the end of 10 seconds.
4. When pilot flame is proven, the sparker
is deactivated, main gas valve 1 and 2
are opened and the vent valve is closed.
5. The pilot valve is deactivated after a 10
second main flame establishing time.
6. The modulating gas valve can modulate
to maintain capacity based on 0-10 VDC
input to the modulating gas valve
controller (the modulating gas valve
controller sends a 0-20 VDC signal to
the modulating gas valve).
Safeties:
1. There is an air flow proving switch
which is a differential pressure switch
that is mounted across the supply blower
bulkhead wall. This switch needs 0.5”
wc to activate.
2. There is an adjustable air side high
pressure switch on the inlet to the burner
profile plate. This setting is application
specific and the setpoint can be located
on the unit nameplate.
3. There is an adjustable air side low
pressure switch on the outlet of the
burner profile plate. This setting is
application specific and the setpoint can
be located on the unit nameplate.
4. There are door interlock switches on the
air stream access doors upstream and
downstream of the burner. These
interlock switches will deactivate the
heater if the doors are open.
5. There is a main limit switch downstream
of the burner. This setting is shown on
the unit nameplate.
6. There is an adjustable manual reset high
gas pressure switch on Main Gas Valve
2. This switch should be set to trip at