Generac Power Systems 55, 75 27- Typical Propane Gas Fuel System, 28– LP Gas Carburetion Diagram

Section 7

DIAGNOSTIC TESTS

DISCUSSION (LPG MODELS):

LP gas is stored in pressure tanks as a liquid. The gas systems used with these generators were designed only for vapor withdrawal 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.

Gas pressure delivered to the solenoid valve must be properly regulated by means of a primary gas regula- tor. 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 inch- es 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.

CAUTION!: Use only approved components in the fuel supply system. All components must be properly installed in accordance with applicable codes. Improper installation or use of unautho- rized components may result in fire or an explo- sion. Follow approved methods to test the sys- tem for leaks. No leakage is permitted. Do not allow fuel vapors to enter the vehicle interior.

LP gas vapors should be supplied to the secondary regulator inlet at about 11 inches water column (posi- tive pressure). The engine pistons draw air in during the intake stroke (Figure 7-28). 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 diaphragm 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 7-27 – Typical Propane Gas Fuel System

NOTE: Recommended MINIMUM gas flow rate for all air-cooled QUIETPACT series generators 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 pri- mary 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 prima- ry regulator that supplies the generator must con- nect directly to a gas pressure tank. Do NOT tee the generator line into a gas circuit feeding other areas.

Figure 7-28 – 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 move- ment of the regulator valve. The more the regulator valve opens, the greater the gas flow that is propor- tional to airflow through the generator.

The following facts about the secondary regulator must be emphasized:

•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.

PROCEDURE:

A water manometer or a gauge that is calibrated in “ounces per square inch” may be used to measure the fuel pressure. Fuel pressure at the inlet side of the LPG Shut Off Valve should be between 11-14 inches

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