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2.5.3 VAPOR WITHDRAWAL
LP gas is stored in pressure tanks as a liquid. The gas systems
used with these generators were designed only for vapor with-
drawal type systems. Vapor withdrawal systems use the gas
vapors that form above the liquid fuel in the tank. Do NOT attempt
to use the generator with any liquid withdrawal type system.
2.5.4 PRIMARY REGULATOR
Gas pressure delivered to the solenoid valve must be properly
regulated by means of a primary gas regulator. Mount the primary
regulator at the gas tank outlet or in the supply line from the gas
tank. The following rules apply:
For best results, the primary regulator supplies gaseous fuel to •
the secondary regulator at 11 inches water column. Do NOT
exceed 14 inches water column.
The installer must be sure the primary regulator is rated at •
sufficient gas flow to operate the generator plus all other gas
appliances in the circuit.
NOTE:
Recommended MINIMUM gas flow rate for all air-cooled gen-
erators is 67 cubic feet per hour.
If an existing primary gas regulator does not have a sufficient
flow capacity for the generator and other gas appliances in the
circuit, (a) install a primary regulator with adequate flow rate,
or (b) install a separate regulator only and rated at least 67
cubic feet per hour. The inlet side of any primary regulator that
supplies the generator must connect directly to a gas pressure
tank. Do NOT tee the generator line into a gas circuit feeding
other areas.
2.5.5 GASEOUS CARBURETION
LP gas vapors should be supplied to the secondary regulator inlet
at about 11 inches water column (positive pressure). The engine
pistons draw air in during the intake stroke (Figure 2.16). This air
passes through a carburetor venturi, which creates a low pressure
that is proportional to the quantity of air being pumped. The low
pressure from the carburetor venturi acts on the regulator dia-
phragm to pull the diaphragm toward the source of low pressure.
A lever attached to the diaphragm opens a valve to permit gas glow
through the carburetor.
Figure 2.16 – LP Gas Carburetion Diagram
The greater the airflow through the carburetor venturi, the lower the
pressure at the venturi throat. The lower the pressure at the venturi
throat, the greater the diaphragm movement, and the greater the
movement of the regulator valve. The more the regulator valve
opens, the greater the gas flow that is proportional to airflow
through the generator.
The following facts about the secondary regulator must be empha-
sized:
The regulator must be sensitive to venturi throat pressure •
changes throughout the operating range.
The regulator must be properly adjusted so it will stop the flow •
of gas when the engine is not running (no air flow through the
carburetor).
The slightest airflow (and vacuum in the venturi throat) should •
move the regulator valve off its seat and permit gas to flow.
2.5.6 FUEL SUPPLY LINES
LP gas lines must be accessible, but protected against possible •
damage.
Do NOT connect electrical wiring to any LP gas fuel line or run •
wiring alongside the lines.
Route gas lines away from hot engine exhausts.•
Retain gas lines with metal clamps that do not have sharp •
edges.
Install an approved length of flexible hose between the gaseous •
fuel solenoid valve and rigid fuel supply lines. The flexible line
must be nonmetallic, nonorganic and nonconductive. It must be
approved for use with LP gas.
2.5.7 EXCESS FLOW VALVE
LP gas tanks should have an excess flow valve, according to
NFPA 501C, Paragraph 3-4.4. This valve and the gas lines must
be carefully sized so the valve will close when a fuel line is severed
or broken. Consult the Natural-LP Gas Association for information
and limitations of excess flow valves.
Manual shutoff valves on the supply tank and elsewhere in the sys-
tem must be fully open when operating the generator. The excess
flow valve functions properly only if all valves are fully open.
2.5.8 LEAKAGE TESTS
Do not place the generator into service until the gas system has
been properly tested for leaks. To test the system, a separate
source of 12 volts DC is needed to open the gaseous fuel solenoid
valve.
The leak test must comply fully with NFPA, Paragraph 318. All con-
nections, hoses, valve regulators, fittings, and other fuel system
parts must be tested under gas or air pressure of not less than
90 psi (620 kPa), while using soap and water or an equivalent
solution to check for leaks. Other approved methods of testing for
leaks may be used, if appropriate. DO NOT USE ANY FLAME TO
TEST FOR LEAKS.
Section 2 – Installation
Recreational Vehicle Generator