Generac Power Systems 005342-6, Owner'S Manual

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6
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.
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 #046622).
DIESEL FUEL SYSTEM
Diesel fuel is supplied to the generator set from a base-mounted
fuel tank.
Diesel fuels are less volatile than gaseous fuels, however, careless
installation can lead to safety hazards and/or serious problems
with engine/generator performance and reliability.
NOTE:
Appropriate care should be taken in applications where
extremely low ambient temperatures are possible to 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 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.
NOTE:
On units with LP gas liquid withdrawal fuel systems, a block
heater is included as standard equipment. The heater is
powered by the UTILITY power source during non-operating
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 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 (0.6 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 consider-
ably 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 accom-
plished by using two regulators, (for example, a line pressure
regulator for natural gas, and a vacuum-operated regulator for LP
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 pres-
sure 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 operating.
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. 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 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.
General Information