HEAD 2A3929 - Caterpillar

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Isolate the LNG tank by closing the shut off valve (4) to the vaporizer and close the vapor isolation valve (9) to ensure that the fuel will flow from the bottom of the tank.
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Connect fuel station fill line (1) and vent line (2) from LNG tank to fuel station.
Hook vent nozzle (2) to LNG tank.
Ensure that the valve on the fuel station is set to OPEN for fuel return (Prefer to vapor space).
OPEN defuel valve (6). This will flow fuel from the LNG tank to the storage.
Monitor tank & fuel station pressures. The pressure building process may need to be repeated. It will be difficult to get final 5-10% of LNG out of the tank.
When no more fuel can be transferred, CLOSE the defuel valve (6) and unhook the fill nozzle (1).
Open the tank isolation valve slowly. A rapid flow of gas/liquid out of the LNG tank may create a pressure pulse that can trip a Pressure Relief Valve (PRV). Be aware that cold gas/fuel will emerge from the vent line on the truck and no personnel should be allowed in that area during the fuel drain process.
OPEN the tank isolation valve (4) slowly to pressurize the system.
OPEN the system manual vent valve (8) slowly and vent the remaining tank pressure to atmosphere through the truck vent circuit.
CLOSE the system manual vent valve (8).
Proceed to purge with Nitrogen. Refer to Purging the Tank.
Disconnect the ground wire.Note: The tank will remain cold for approximately a day. The remaining vapors and liquid may increase the pressure in the tank.If the LNG tank is empty for more than a day, plan to use the warm tank fill procedure. Refer to First Fill Warm Tank with Nitrogen Charge.Purging the Tank
The LNG tank must be purged completely of flammable gas before maintenance may begin. Never work on the machine fuel system or LNG tank without completely purging it of flammable gas. The LNG tank must be purged completely before shipping it for repair.Purging the tank will completely remove 100% of all liquid from the tank. The remaining vapor will be diluted with Nitrogen to levels lower than flammability limits. The tank will be rendered non-flammable. This will ensure that the truck is safe to bring indoors for servicing.
Nitrogen displaces oxygen that may result in asphyxiation. This procedure must be performed in a well ventilated area.
Nitrogen from a liquid cylinder or compressed gas cylinder is the recommended purge gas. Use a compressed gas pressure regulator to reduce the pressure from the nitrogen gas source to approximately 690 kPa (100 psi).
Do not use compressed air for purging. Using compressed air for purging will create an explosive mixture with the LNG fuel. Could cause serious injury or death.
The tank must be purged outdoors in an open area away from open flame, electrical equipment, and other ignition sources. Before purging the tank, it must be defueled completely of LNG.
Prepare the machine for maintenance. Refer to "Operation and Maintenance Manual" SEBU7173 , Prepare the Machine for