Inspection Intervals Defined by U.S DOT’s FMVSS 304
- All CNG cylinders must be inspected after any fire or accident, regardless of vehicle GVWR.
- For vehicles with GVWR of less than 10,000 pounds, CNG cylinders must be inspected at least every 3 years or 36,000 miles, whichever comes first.
- For vehicles with GVWR of 10,000 pounds or greater, CNG cylinders must be inspected at least every 12 months
Four Types and Intervals for Inspections
| Inspection Type | When Performed? | Inspection Level | What is Inspected? | Who Performs? |
|---|---|---|---|---|
| Pre-Service Inspection | Prior to placing vehicle in service | Detailed Visual Inspection | Thorough inspection of all high pressure components, including cylinders | A certified or qualified CNG Fuel System Inspector |
| Driver Pre- and Post-Trip Inspection | Before and after each trip in a CNG vehicle | Cursory Visual Inspection | All visible components and cylinder shields | Driver |
| General Visual Inspection | During any preventive maintenance/service | General Visual Inspection | All visible components, with special attention to cylinder shields | Trained Vehicle Technician |
| Detailed Visual Inspection | After any fire or accident. Vehicles <10,000 pounds GVWR at least every 3 years/36000 miles, whichever come first. Vehicles 10,000 pounds GVWR or greater at least every 12 months | Detailed Visual Inspection | Thorough inspection of all high-pressure components, including cylinders | A certified or qualified CNG Fuel System Inspector |
What Is Covered in the Detailed Visual Inspection?
In 2008, the NGV industry adopted a best practice to inspect not just the cylinders, but the entire high pressure CNG fuel system. This includes:
- Fuel Receptacle
- Secondary Check Valve
- Defueling System
- Fittings, Tubing and Lines
- Cylinder(s)
- Cylinder Shields and Mounting System
- Cylinder Valves
- PRDs, Vent Lines and Caps
- Fuel System Isolation Valve
- High Pressure Coalescing Filter
- Fuel Shutoff Solenoid
- Pressure Gauge
- Pressure Regulator
- Components/Labels
What Records are Required?
For each Detailed Visual Inspection, a completed CNG Fuel System Inspection form and accompanying photos should be retained. Inspection records are not required to be submitted to any regulatory agency or manufacturer.
At the conclusion of each Detailed Visual Inspection, a “Passed” or “Failed” inspection label should be affixed to each cylinder installed on the vehicle.
