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CNG Fuel System Inspection Requirements

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 TypeWhen Performed?Inspection LevelWhat is Inspected?Who Performs?
Pre-Service InspectionPrior to placing vehicle in serviceDetailed Visual InspectionThorough inspection of all high pressure components, including cylindersA certified or qualified CNG Fuel System Inspector
Driver Pre- and Post-Trip InspectionBefore and after each trip in a CNG vehicleCursory Visual InspectionAll visible components and cylinder shieldsDriver
General Visual InspectionDuring any preventive maintenance/serviceGeneral Visual InspectionAll visible components, with special attention to cylinder shieldsTrained Vehicle Technician
Detailed Visual InspectionAfter 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 monthsDetailed Visual InspectionThorough inspection of all high-pressure components, including cylindersA 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.