A Twin City Fan Company
5959 Trenton Lane • Minneapolis, MN 55442-3238
Phone (612) 551-7500 • Fax (612) 551-7501 • www.aerovent.com
Units ordered with the high-low fire option are supplied
with a 1" NPT SR600 two-stage valve mounted in the
pipe train.
The SR600 provides an economical means of flame
staging where infinite modulation is not required. Turn-
down on low-fire is from 25% to 75% of high-fire. This
valve is powered by a 24 volt AC transformer. When the
coil is energized, the valve is at low-fire. When the coil
is de-energized, it is at high-fire.
Adjustments
To check the minimum or low-fire and maximum or
high-fire pressures for the limits of modulation or stag-
ing, use the following procedures:
To set minimum or low-fire
1. Remove cover plate
➀
.
2. Remove high fire adjusting screw
➁
, spring
➂
, and
plunger
➃
. A small magnet is useful for this purpose.
Handle plunger carefully to avoid marring or collect-
ing dirt. Do not lubricate.
3. Modulation or Staging: Using low-fire adjusting
screw
➄
, set manifold pressure to manufacturer’s
specifications (50% to 75% of high-fire).
4. Modulation or Staging: Cycle solenoid gas valve to
check for proper ignition.
5. Modulation or Staging: Adjust air shutter or increase
low-fire adjustment if needed.
6. Replace plunger, spring and high-fire adjusting
screw.
To Set Maximum or High-Fire:
Note:
To avoid danger of over-firing, make certain that
inlet pressure is at 1.0" w.c. above the outlet pressure.
High-Low Fire Option
1
2
3
5
4
Make sure
plunger is
installed as
above.
1. Modulation and Staging: Using high-fire adjusting
screw
➁
, set manifold pressure to manufacturer’s
specifications. See page 1, Fig. 1.
2. Staging Only: Cycle burner to check performance.
3. Replace cover plate.
