Fuel Consumption; Fuel Pressure; Power Loss; Fuel Pipe Sizing - Briggs & Stratton Fortress Installation And Operation Manual

Fuel Consumption

Estimated fuel supply requirements at half and full load
for natural gas and LP vapor fuels are shown below.
LP Vapor (Propane)
Cu Ft/Hr
Gal/Hr
Full Load
(liquid)
BTU/Hr
Cu Ft/Hr
Gal/Hr
3/4 Load
(liquid)
BTU/Hr
Cu Ft/Hr
Gal/Hr
1/2 Load
(liquid)
BTU/Hr
Cu Ft/Hr
Gal/Hr
1/4 Load
(liquid)
BTU/Hr
Cu Ft/Hr
Gal/Hr
Exercise
(liquid)
BTU/Hr
Natural Gas
Cu Ft/ Hr
Full Load
BTU / Hr
Cu Ft/ Hr
3/4 Load
BTU / Hr
Cu Ft/ Hr
1/2 Load
BTU / Hr
Cu Ft/ Hr
1/4 Load
BTU / Hr
Cu Ft/ Hr
Exercise
BTU / Hr
18
20kW 17kW
135 118
3.75 3.28
337500 295000
109 99
3.03 2.75
272500 247500
83 74
2.31 2.06
207500 185000
56 54
1.56 1.5
140000 135000
40 40
1.11 1.11
100000 100000
20 kW 17 kW
(18 kW) (15.3 kW)
260 248
260000 248000
240 218
240000 218000
187 170
187000 170000
135 128
135000 128000
99 99
99000 99000
Recommended
Energy Content of
Fuel
Heating Value:
BTU per gallon (gross**)
Cubic feet (gas)

Fuel Pressure

Both LP vapor and natural gas fuel supply pressure
at the generator's fuel inlet port should be between
the following levels at full load with all gas appliances
turned on and operating.
• NG is 3.5-7"
• LP is 11-14" W.C.
Ensure that all gas line shutoff valves are OPEN and
that adequate fuel pressure is available whenever
automatic operation is desired.
For natural gas fuel pressure levels of 3.5-5" W.C.,
replace regulator assembly with service kit 6331-00.

Power Loss

Air density is less at high altitudes, resulting in less
available engine power. Specifically, engine power
will decrease 3.5% for each 1,000 feet (300 meters)
above sea level and 1% for each 10° F (5.6°C) above
77°F (25°C). Make sure you and your installer consider
these factors when determining total generator load.

Fuel Pipe Sizing

There are numerous on-line or otherwise-published
references for fuel pip sizing. For example, NFPA
54-Natural Fuel Gas Code, 2006 (Item #: 320-6031-06)
is a common resource.
The installer should consider the specific gravity of gas
and compensate for a nominal amount of restriction
from bends, fittings, etc. If an unusual number of
fittings, bends, or other restrictions are used, refer to
federal and local codes for guidance.
LP Vapor Natural
Gas
91,547
2,500 1,000