Defueling CNG

c2 dm 20.03.002

Follow the instructions below for defueling, if the CNG cylinder(s) need to be emptied for any reason.

  1. Prepare the vehicle for defueling.
    1. Park the vehicle on a level surface, shut down the engine, and set the parking brake. Chock the tires.
    2. Turn the battery disconnect switch to the off position.
    3. Open the fuel access door.
    4. Note the fuel pressure on the high-pressure gauge (CNG tank pressure).
    5. Turn the three-way defueling valve to the vent position.
    6. Ground the CNG defueling hose to the ground bolt.
    7. Connect the CNG defueling hose to the vehicle by pulling back on the quick-connect collar on the hose and then push it on the vehicle coupler to make the connection.
  2. Carefully attach the CNG defueling hose to the fuel connection on the empty storage tank and open the fuel valve on the nozzle, if so equipped.
  3. CNG can be defueled from the vehicle to the empty storage tank. Slowly turn the three-way valve from the vent position to the defuel position on the vehicle.
  4. Adjust the fuel flow to a steady flow rate. Too fast of a flow rate will cause the system to freeze up.
  5. When the gas stops flowing, look at the high-pressure gauge and verify the gas pressure. The CNG tank pressure gauge on the vehicle should be at or near zero.

    6. Warning: Fuel pressure in the hose will vent through the defuel valve on the vehicle. Natural gas fuel tanks, lines, and valves are always pressurized. Always observe safety precautions. Failure to do so could lead to loss of control over a filling hose or to ignition of the natural gas, which could cause serious bodily injury, death, or severe property damage.

  6. Turn the three-way valve on the vehicle from the defuel position to the vent position, and disconnect the hose from the fuel connection on the storage tank.
  7. Turn the three-way valve on the vehicle from the vent position to the off position.
  8. Disconnect the fuel hose from the vehicle. Pull back on the quick connect collar on the hose and pull the hose away from the vehicle coupler.
  9. Remove the defueling hose from the ground bolt.
  10. With the tires chocked, turn the battery disconnect switch to the on position and start the engine.
  11. Operate the engine at high idle until the engine stalls. Verify that the CNG tank pressure gauge reads zero after the engine stalls. Ensure that the engine will crank, but not start.
Note:
Parent topic: Fuel Tank Filling Procedures
Document Number: 0000107356
Manual Publication Date: 2024-05-07
Topic Publication Date: 2024-05-06