G3408C and G3412C Engines Caterpillar

Gas Pressure

Usage:

The correct air/fuel ratio is very important for the following considerations:

Margin of detonation
Control of emissions
Achieving optimum service life for the engine

If the air/fuel ratio is not appropriate for the fuel and the operating conditions, a failure of the engine may occur. The service life of the turbocharger, the valves, and other components may be reduced.

Make sure that the pressure of the gas to the gas pressure regulator is sufficient.

For low pressure gas, pressure of 10 to 35 kPa (1.5 to 5 psi) is required for the gas pressure regulator.

Fluctuations of the fuel pressure can change the air/fuel ratio. For low pressure gas fuel systems, the maximum fluctuation that is allowed in the fuel pressure to the engine is ± 1.7 kPa (± 0.25 psi).

Gas Pressure Regulator

The gas pressure regulator maintains a pressure differential between the air and the fuel that is supplied to the carburetor. After setting, the gas pressure regulator will maintain the pressure differential in response to changes in the air pressure.

Determine whether the pressure regulator uses positive pressure or negative pressure.

For engines with dual fuel systems, both of the regulators must be adjusted.

A water manometer is used to measure the pressure differential. This measurement is taken when the engine is operating at high idle rpm. When a load is applied, the fuel pressure will usually decrease by approximately 0.25 to 0.50 kPa (1 to 2 inches of H₂O). If the performance of the gas pressure regulator is erratic, the gas pressure regulator may require service.

Installation Before the Gas Pressure Regulator

To prevent particles from entering the engine, install a one micron fuel filter 1 m (3 ft) before the gas pressure regulator. The recommended filter is the 4P-4717 Fuel Filter with the 4P-4720 Gas Filter Element .

Install a pressure gauge on each side of the fuel filter in order to monitor the filter's restriction. To facilitate servicing of the filter, install a shutoff valve on the supply side.

Adjusting the Gas Pressure to the Engine

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Table 1
Tools Needed	Qty
8T-5160 Gas Regulator Setting Tool	1

Adjusting the Positive Pressure Regulator

Make sure that the gas to the gas pressure regulator is shut OFF.

Note: A water manometer may be used instead of the 1U-5470 Engine Pressure Group .

Attach the lines for the differential pressure gauge of the 1U-5470 Engine Pressure Group .

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Illustration 1	g00777970
Typical arrangement for low pressure gas (1) Plug in the gas line to the carburetor (2) Air filter service indicator on the air cleaner (3) Cap

Remove plug (1). Remove service indicator (2) from the air cleaner. Attach the lines for the differential pressure gauge of the 1U-5470 Engine Pressure Group into the openings.

Remove cap (3) .
The nut for adjusting the gas pressure regulator is under the cap.

Turn ON the gas supply to the gas pressure regulator. Observe the pressure differential.
The correct pressure of the gas is 1.0 to 1.2 kPa (4 to 5 inches of H₂O) HIGHER than the atmospheric pressure.

If necessary, adjust the gas pressure regulator in order to obtain the desired pressure. Use the 8T-5160 Gas Regulator Setting Tool or use a large screwdriver to turn the nut.

Start the engine. Operate the engine at rated speed (no load). Observe the pressure differential. Adjust the gas pressure again, if necessary.

Stop the engine. Turn OFF the gas supply to the gas pressure regulator.

Remove the lines for the differential pressure gauge. Install the original parts (1), (2), and (3) into the openings.

Turn ON the gas supply to the gas pressure regulator.

Adjusting the Negative Pressure Regulator

Note: For dual fuel systems, use the negative pressure regulator for the gas with the fuel energy content that is higher.

Make sure that the gas to the gas pressure regulator is shut OFF.

Note: A water manometer may be used instead of the 1U-5470 Engine Pressure Group.

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Illustration 2	g00778139
Typical arrangement of gas pressure regulators for a dual fuel system that uses low pressure gas (1) Plug in the gas line to the carburetor (2) Cap

Remove plug (1). Remove the service indicator from the air cleaner. Attach the lines for the differential pressure gauge of the 1U-5470 Engine Pressure Group into the openings.

Remove cap (2) .
The nut for adjusting the gas pressure regulator is under the cap.

Turn ON the gas supply to the gas pressure regulator. Observe the pressure differential.
The correct gas pressure is approximately -0.25 kPa (-1 inch of H₂O) LOWER than the atmospheric pressure.

If necessary, adjust the gas pressure regulator in order to obtain the desired pressure. Use the 8T-5160 Gas Regulator Setting Tool or use a large screwdriver to turn the nut.