Dazo Water Fuel Technology

3.2.2 Operation and Maintenance

Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency.

During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks.

When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots.

Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks.

Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak.

Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.

Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.

Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual.

Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks).

Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24-VDC battery.

Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion.
Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided.

Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.

Do not smoke or use a cell phone when servicing or fueling the vehicle.

The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled.