Generac Power Systems QT100, Owner'S Manual, Page: 9 / 80

FUEL SYSTEM
FUEL REQUIREMENTS
The Stationary Emergency Generator may be equipped with one of
the following fuel systems:
• Natural gas fuel system
• Propane vapor (PV) fuel system
• Liquid propane (LP) fuel system
Recommended fuels should have a Btu content of at least 1,000
Btu's per cubic foot for natural gas; or at least 2,520 Btu's per
cubic foot for LP gas. Ask the fuel supplier for the Btu content of
the fuel.
Required fuel pressure for natural gas is 11 inches to 14 inches
water column (0.4 to 0.5 psi); and for liquid propane, 11 inches
to 14 inches of water column (0.4 to 0.5 psi).
NOTE:
Any piping used to connect the generator to the fuel supply
should be of adequate size to ensure the fuel pressure NEVER
drops below 11 inches water column for natural gas or 11
inches water column for liquid propane for all load ranges. The
fuel supply piping shall be sized according to the installation
manual using the fuel consumption requirements identified in
the Specifications section of the Owner's Manual.
NOTE:
It is the responsibility of the installer to make sure that only
the correct recommended fuel is supplied to the generator fuel
system. Thereafter, the owner/operator must make certain that
only the proper fuel is supplied.
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 distribu-
tion line to the standby generator site. The following information
applies to natural gas fuel systems.
• 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 solenoid should not
exceed approximately 14 inches water column (0.5 psi).
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 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.
• When ambient temperatures are low and engine fuel consump-
tion is high, the vapor withdrawal system may not function
efficiently.
• Ambient temperatures around the supply tank must be high
enough to sustain adequate vaporization, or the system will not
deliver the needed fuel volume.
• In addition to the cooling effects of ambient air, the vaporization
process itself provides an additional cooling effect.
LP FUEL SYSTEM
LP is supplied as a liquid in pressure tanks. It is usually 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 provide
the necessary heat for conversion of the fuel from a liquid to a
gaseous state.
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Fuel System