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It is the responsibility of the installer to make sure
that only the correct recommended fuel is sup-
plied to the generator fuel system. Thereafter, the
owner/operator must make certain that only the
proper fuel is supplied.
For further information on the various types of
fuel systems, refer to Engine-Generator Standby
Electric Power Systems Installer's Guide and
Reference Manual (part #46622).
DIESEL FUEL SYSTEM
Diesel fuel is generally supplied to the generator set
from a suitable day tank or base-mounted fuel tank.
Either of these tanks may be used in conjunction with
a main (bulk) supply tank.
Diesel fuels are less volatile than gaseous fuels, how-
ever, careless installation can lead to safety hazards
and/or serious problems with engine/generator per-
formance and reliability.
Appropriate care must be taken in applications
where extremely low ambient temperatures are
possible. Ensure the temperature of the diesel fuel
is not allowed to fall below levels where "gelling"
could occur.
LP FUEL SYSTEM
LP is supplied as a liquid in pressure tanks. It is usu-
ally made up of propane, butane, or a mixture of the
two gases. Propane tends to vaporize readily even at
temperatures as low as -20° F (-29° C). However,
butane reverts to its liquid state when temperatures
drop below 32° F (0° C).
LP in a liquid withdrawal system must be converted
to its gaseous state before it is introduced into the
engine carburetor. A vaporizer-converter is generally
used to accomplish this. In such a converter, heated
engine coolant is ported through the converter to pro-
vide the necessary heat for conversion of the fuel
from a liquid to a gaseous state.
On units with LP gas liquid withdrawal fuel sys-
tems, a block heater is included as standard
equipment. The heater is powered by the UTILITY
power source during nonoperating periods. Thus,
heated coolant is always available to aid the fuel
vaporization process.
NATURAL GAS FUEL SYSTEM
Natural gas is supplied in its vapor state. In most
cases, the gas distribution company provides piping
from the main gas distribution line to the standby
generator site. The following information applies to
natural gas fuel systems.
6
Generac
®
Power Systems, Inc.
Section 1 – General Information
Generac Standby Generator Sets
NOTE:
NOTE:
NOTE:
• Gas pressure in a building is usually regulated by
national, state and local codes.
• To reduce gas pressure to a safe level before the gas
enters a building, a primary regulator is needed.
The natural gas supplier may or may not supply
such a regulator.
• It is the responsibility of the gas supplier to make
sure sufficient gas pressure is available to operate
the primary regulator.
• Gas pressure at the inlet to the fuel shutoff sole-
noid should not exceed approximately 15 inches
water column (0.75 psi). Optimum pressure at the
fuel shutoff solenoid is 11 inches water column
(0.4 psi).
COMBINATION LP/NATURAL GAS
FUEL SYSTEM
In some areas, the cost of natural gas may be reduced
considerably by procuring the gas on "interrupted
service" rates. Such rates may be obtained by using
LP gas as an emergency fuel when natural gas is not
available. Automatic changeover is accomplished by
using two regulators, i.e., a line pressure regulator
and a vacuum-operated regulator for natural gas. The
difference in pressure compensates for the greater
Btu value of LP gas.
During operation on natural gas, a positive pressure
exists in the common line to the carburetor. This
pressure closes the LP gas regulator and stops the
flow of LP gas. Loss of natural gas pressure causes a
partial vacuum in the line, and the LP gas regulator
then opens to admit LP gas into the system. Adjusting
a separate power mixture in the LP gas line permits
precise setting of air-to-fuel ratios on each of the
fuels. Changeover is automatic with the engine oper-
ating.
PROPANE VAPOR WITHDRAWAL FUEL
SYSTEM
This type of system utilizes the vapors formed above
the liquid fuel in the supply tank. Approximately 10
to 20 percent of the tank capacity is needed for fuel
expansion from the liquid to the vapor state. The
vapor withdrawal system is generally best suited for
smaller engines that require less fuel. The installer
should be aware of the following:
• The Generac natural gas and LP gas systems are
similar. However, the natural gas system delivers
gas at a pressure of approximately five inches
water column to the carburetor. The LP gas system
delivers gas at a slightly negative pressure (about
negative one inch) to the engine carburetor.
• When ambient temperatures are low and engine
fuel consumption is high, the vapor withdrawal
system may not function efficiently.
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