Inspection of the Natural Gas Fuel System
- Inspect fuel tanks for dents, scratches, gouges, or other
signs of damage. Inspect the fuel lines and connections for leaks.
Check that the fuel tanks are securely mounted. Look for signs of abrasion between components.CNG Fuel System : Ensure that the CNG fuel cylinder storage box is secured to the frame. Inspect for signs of looseness.(LNG Fuel System : Ensure that the LNG fuel tank is secured to the mounting brackets and that the mounting brackets are secured to the frame. Ensure all rubber isolator straps are secure around the LNG fuel tank.
- Check for the presence of all required decals present in
the following locations:
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Gas detection system overhead console;
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Above the door handle on both doors;
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Left front bumper;
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End-of-frame crossmember;
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LNG fuel tank fill port (maximum psi), if equipped.
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- Check for the presence of vent caps on pressure relief
valves and devices. See Fig.. If any caps are missing,
have the fuel system inspected by a qualified technician.CNG Fuel System : Each fuel cylinder should have two caps (one on each end), which are visible on the back of the CNG fuel cylinder storage box. One additional cap is located on the pressure relief valve on the inboard side of the CNG fuel box, next to the fuel outlet line. If equipped with saddle tanks, there are also two vent tubes with caps between the back of the cab and the back-of-cab fuel tanks.
Fig. 1, CNG Vent Line Caps
Fig. 2, LNG Tank Plumbing Components
- Inspect all plumbing components, including the fuel shutoff
valve(s), primary and secondary relief valves, and the LNG vapor shutoff
and excess flow valves, if equipped, for signs of damage or leaks.
See Fig. or
see Fig..Inspect the fuel fill fitting for signs of damage or leaks.Inspect all lines for signs of leaks or damage, and check all threaded connections.
Fig. 3, CNG Fuel Panel
- Inspect all fuel gauge components for signs of leaks or damage. Inspect the fuel level sender cable and wiring.
- Inspect all coolant hoses for signs of chafing, kinks, or leaks. The CNG fuel system utilizes coolant hoses between the engine and the pressure regulator inside the fuel panel. The LNG fuel system utilizes coolant hoses between the engine and the vaporizer.
- If equipped with an LNG fuel system, check the fuel tank pressure gauge to ensure that pressure is within the normal range of 120 to 150 psi (827 to 1034 kPa). If tank pressure exceeds 230 psi (1586 kPa) and the pressure relief valve does not open automatically, vent the tank immediately.
- Inspect the LNG vaporizer for signs of damage or leaks. See Fig.. Inspect the vaporizer mounting brackets for signs of looseness.
- On CNG systems, check the low pressure fuel filter(s) at
the engine for contamination.
- Turn the engine off and remove the key form the ignition.
- Slowly open the drain petcock and drain any fluid into an appropriate container.
- When fluid stops, close the drain petcock.
- Examine the fluid.If more than approximately one ounce of oil or other contaminants is found, have the system checked at a qualified service center.
Warning: As with all pressure vessels, CNG/LNG storage and fuel delivery systems are inherently dangerous and should be treated as such. Beyond the visual inspections listed below, all maintenance and repairs to compressed natural gas (CNG) or liquified natural gas (LNG) systems should be performed by trained personnel. Individuals who are not trained in all aspects concerning CNG/LNG fuel delivery systems are not permitted to service, maintain, test, or inspect a system in any way. Failure to comply with safety regulations may lead to fire or explosion, resulting in property damage, personal injury, or death.