SPECIAL FUEL SYSTEMS
PRECAUTIONS
When properly installed and maintained, a gas fuel system can be just as safe as any other fuel
system.
While gas and gasoline are both highly volatile and flammable, gas presents an
addit~onal
danger in that it is heavier than air and tends to settle in low areas where even the slightest spark could
ignite the gas. Because of this, extra precautions must be taken to insure safety when using gas as an
engine fuel.
The following precautions are offered not to discourage the use of gas but rather as
reminders to exercise care in the
handllng of gas fuel. While adherence to federal, state and local
laws governing gas systems lessens the potential dangers, good common sense is the final safeguard in
installing, handling or repairing engines with gas fuel systems.
Installation and subsequent repair of gas fuel systems must he done only by qualified gas system
technicians.
Gas must never he used for pressure testing of new or rebuilt gas equipment
--
compressed air
will do the job safely.
Never
bleed gas out of any part of a gas system to check flow of gas or when adjusting, for
example, gas regulators.
Compressed air should be used for these purposes.
An engine with
a
gas fuel system must never be installed or operated in a poorly ventilated area
where leakage of gas could endanger the safety of building occupants or persons in the vicinity.
GAS
SYSTEMS
Natural gas and liquefied petroleum gas (LPG) systems are used on the two cylinder engines.
These systems require special equipment including gas carburetors (or gasoline carburetors with gas
adapters) and primary and secondary regulators.
In
some
applications,
a
2
-
stage regulator is used
--
this provides both primary and secondary regulation.
Natural gas, as supplied from main transmission lines, is normally received at pressures not
greater than
50
pounds per square inch (psi). With LPG (butane or propane or
a
mixture of the two
gases) the pressure may go
as
high as
180
-
200
psi depending on the mixture and the prevailing tempera
-
tures.
To
be used by the engine, the pressure must he reduced to about
4
to
6
ounces per square inch.
The fuel supplier should insure that gas pressure is sufficient to operate the primary regulator.
If pressure drops too low, the regulator may not function at all.
While propane tends to maintain some
vaporizing pressure even at temperatures down to
-
20
"
F.,
butane returns to liquid state and offers
little or no vapor pressure when the temperature drops to freezing or
32
"
F.
For this reason, fuel
suppliers usually supply LPG of higher butane content in hot weather but will alter this to
a
higher per
-
centage of propane during cold weather.
If this ratio is not changed, starting and operating difficulties
may be encountered in cold weather.
Two different types of LPG systems are used. One system, the vapor withdrawal system, utilizes
vapor that normally forms in the space
above the Liquid fuel in the tank.
To allow for expansion of the
gas from Liquid to vapor, the maximum Liquid level
is
usually held at about
80
or
90
per cent of the total
capacity of the tank.
With this system, the temperature of the air surrounding the tank must be high
enough to sustain adequate vaporization of the fuel.
The other LPG system is the liquid withdrawal system. On this type, liquid fuel
is
drawn out of
the tank and introduced into a vaporizer which is mounted so that air heated by the engine is used to
change the liquid fuel into vapor.
The usual regulatory equipment must also be used with this system.
Since the
gas carburetor receives fuel in vapor state, it does not have to provide further vapori
-
zation
as
does a gasoline carburetor.
The gas carburetor therefore serves only to control the ratio of
gas to air under varying load and speed conditions. There are two basic types of gas carburetors used
on
Kohler two cylinder engines. One type utilizes the venturi and nozzle system while the other type
uses a diaphragm which is activated by pressure differential.
in
a
venturi type carburetor, the gas nozzle is located at the point of greatest pressure drop
inside the venturi.
This creates a suction within that nozzle that varies with changing rate of air flow
and causes a greater volume of gas to be metered at heavier loads and a lower volume at lighter engine
load.
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