Briggs & Stratton FORTRESS Series Installation And Operation Manual page 18

recommendation values that follow can cause
performance problems.
• In engines set up to run on propane (LP), commercial
grade HD5 propane with a minimum fuel energy of 2500
BTUs/ft3 with maximum propylene content of 5% and
butane and heavier gas content of 2.5% and minimum
propane content of 90% is required.
Natural gas rating will depend on specific fuel, but typical
derates are between 10 and 20% of the LP gas rating.
Natural gas or LP engines are certified to operate on natural
or liquid propane gas. The emissions control system for this
engine is EM (Engine Modifications).
Fuel Pressure
Both LP vapor and natural gas fuel supply pressure at the
generator's fuel inlet port and must be between the following
levels at full load with all gas appliances turned on and in
operation.
• NG is 3.5-7" W.C.
• LP is 11-14" W.C.
Make sure that all gas line shutoff valves are OPEN and
that adequate fuel pressure is available whenever automatic
operation is desired.
Power Loss
Air density is less at high altitudes, resulting in less available
engine power. Engine power will decrease by 3.5% for each
1,000 feet (300 m) above sea level and by 1% for each
10° F (5.6°C) above 77°F (25°C). Generators located in
these conditions must have their transfer switch adjusted
appropriately for this power decrease. See your Automatic
Transfer Switch manual on how to adjust for the power
decrease.
The Gaseous Fuel System
Fuel Pipe Sizing
NFPA 54 and 58 are common resources. The installer must
consider the specific gravity of gas, compensate for a nominal
amount of restriction from bends and fittings, and refer to
federal and local codes for guidance.
Fuel Conversion
The engine of your generator system is factory Calibrated and
set to operate on natural gas (NG). It can also be operated on
liquefied petroleum (LP) vapor.
NOTICE The initial factory NG settings are:
• Screw C: 2.5 turns
• Screw D: 0.5 turns
To configure 12kW units for LP fuel use:
1. Push the ON/OFF Switch (A) on the side of the generator
to the "OFF" (0) position.
2. Remove utility power to the generator to de-energize the
battery charger.
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3. Remove the roof.
4. Remove the 15 Amp fuse (B) from the fuse holder at top
of the control box.
5. Disconnect the negative (-) cable at the battery.
6. Using a slotted screwdriver turn screws (C and D)
clockwise until they are snug (over tightening can
damage the mixer port).
7. Using a slotted screw driver turn screw (C)
counterclockwise ¼ turn.
8. Leave screw (D) seated.
9. Connect the negative (-) cable at the battery.
10. Install the 15 Amp fuse (B) into the fuse holder at top of
the control box.
11. Install the roof.
12. Push the ON/OFF Switch (A) on the side of the generator
to the "ON" (I) position.
13. Open Control Panel access door.
14. Push and hold the CONFIG button to access the
configuration menu.
15. Push SELECT to edit the items in the configuration menu.
16. To setup the generators control board for LP fuel you will
need to enter the Configuration Menu by using the Dealer
Password, which is available on the Power Portal.
17. Navigate to "SELECT PROFILE" and press select on the
correct profile for the generator. For example "12KW_LP"
for operating a 12kW unit running on LP fuel.
NOTICE Selecting a profile that is not intended for the
generator can cause the generator to run erratically and
could result in damage.
18. To Save the new fuel setting, press and hold the STOP/
CONFIG button until "Saving Settings..." is displayed.
19. For Additional information on the operation of the
generator controller please refer to the "Operation
Instructions GC1031 GENSET Controller Manual,"
PN: 80086364.