Fuel Tank Regulations

Gravity Feed Systems – Legal or Not Legal?

Transfer Flow Inc. has designed, manufactured, and installed aftermarket and original equipment gasoline and diesel auxiliary fuel systems worldwide since 1983. As a result, Transfer Flow has invested hundreds of thousands of dollars in testing and engineering to be compliant with North American regulatory agencies while maintaining engineering best practices used in the automotive industry. Many state and federal agencies regulate fuel systems, including the US Department of Transportation (DOT), the National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations (CFR), Federal Motor Vehicle Safety Standards (FMVSS), California Code of Regulations (CCR), and the California Air Resources Board (CARB), to name a few. Due to DOT ambiguity, the absolute legality of gravity fed systems remains unclear. However, Transfer Flow believes safety and legality issues can occur with gravity feed auxiliary fuel systems that may violate portions of US DOT regulation 49 CFR 393.67, a requirement of ALL fuel systems.

From a vehicle performance standpoint, gravity feed fuel systems can adversely affect federally mandated, manufacturer implemented, on-board vehicle diagnostic systems. In the case of many newer vehicles, a gravity fed system keeps the main fuel tank overfull and will likely result in a diagnostic trouble code. In addition to being a nuisance, drivers may miss valid vehicle issues because the check engine light remains on.

In all diesel fuel systems there is a rollover valve which is normally open to atmosphere. The rollover valve utilizes a combination of float weight, spring force, and buoyancy to function properly. When the float is immersed in fuel, the float (valve) closes, effectively preventing fuel leakage in the event of a rollover. The overfill tendencies of gravity fed systems leads some users to seal (effectively eliminate) the rollover OEM valve(s). In the absence of a rollover valve, the auxiliary tank will likely continue to flow fuel into the vapor space of the main fuel tank. If the vapor space in the main tank is diminished, it violates the “overfill restriction” requirement of 49 CFR 393.76(12)(i).

A properly functioning rollover valve will close when the fuel level reaches the float of the valve. Some rollover valves are designed to leak above a certain pressure to meet the “safety venting” requirements of 49 CFR 393.67(8). Capping the rollover valve causes a non-compliance with the “overfill restriction” portion of 49 CFR 393.67(12) (i) and (ii), and is also a violation of the 1990 Clean Air Act.

Safety concerns reach beyond simply spilling fuel during normal operation of gravity fed fuel systems. If the transfer fuel hose in a gravity fed system is damaged, fuel would NOT stop flowing until the transfer tank is empty, resulting in a hazardous condition, and a violation of the 1990 Clean Air Act.

In order to meet more stringent emissions requirements, new diesel pickups utilize some type of active Diesel Particulate Filter (DPF). To maintain performance, the DPF unit has to go through a regeneration cycle where in some vehicles fuel is injected into the catalyst bed of the DPF and burned. During regeneration, many DPF units reach temperatures of 600°C (1,112°F). Diesel fuel has an autoignition temperature of approximately 260°C. Fuel leaking from a rollover valve on a gravity fed system would be in close proximity to the DPF and the possibility of fire is significant. If the gravity fed system overfills the main tank by introducing fuel into the vapor space, there is a potential for fire.

Another consideration is tank pressure. Insufficient vapor space in gravity fed systems might create pressure build-up in the main fuel tank, causing fuel to leak past the anti-siphon/anti-expulsion valve thus, when removing the fuel cap, the operator may be sprayed with fuel.

We believe in the value of NHTSA’s Fuel System Integrity testing utilizing the FMVSS 301 standards. Product development confirmed by FMVSS 301 has been instrumental in Transfer Flow designing the safest aftermarket fuel tanks and fuel systems available. We are proud of our investment in crash tests, and are confident in the safety and legality of our fuel systems. Transfer Flow’s engineering staff has evaluated on-road gravity fed auxiliary fuel systems and has determined that due to safety, environmental, and legal concerns, which are inherent in the design and performance of gravity fed auxiliary fuel systems, Transfer Flow Inc. will not endorse or promote the design, installation, or use of on road gravity fed auxiliary fuel systems. Customer safety and fuel system legality continue to be our priorities after more than 175,000 fuel systems sold and more than 30 years in business.

Transfer Flow fuel tanks are safe, legal, and reliable

  • Fuel Tanks are baffled to prevent fuel slosh
  • Fuel Tanks are pressure tested for leaks
  • Meets emissions regulations of the California Air Resources Board, U.S. Department of Transportation (DOT) and Environment Protection Agency (EPA)
  • Meet California Air Resources Board and EPA requirements concerning fuel fill rates and regulations
  • Meet the fastener (strap) regulations specified by the American National Standards Institute (ANSI) and National Fire Protection Association (NFPA) and required by the Recreation Vehicle Industry Association (RVIA)
  • Designed using, as a minimum, 14-gauge aluminized steel
  • Aluminum diamond plate in-bed tanks are 1/8” thick aluminum
  • Liquid-filled fuel tanks are subjected to a 44 foot drop test, and cannot leak
  • Transfer Flow fuel tanks are NEVER to be used in conjunction with gravity feed fuel systems.

Our refueling tanks meet U.S. Department of Transportation (DOT) regulations

The DOT has issued Transfer Flow DOT Special Permit SP-11911 to manufacture and sell refueling tanks that can store gas, diesel, ethanol, methanol, kerosene and aviation fuel. Transfer Flow refueling tanks meet or exceed the testing and certification requirements specified in 49 CFR 178.803. The following guidelines must be adhered to when installing and using a Transfer Flow refueling tank:

  • Refueling tanks are designed to be mounted near the head gate in a pickup box, flat bed or utility box (no other location on the pickup or truck is recommended)
  • Transfer Flow refueling tanks must be attended to at all times during loading and unloading by a qualified person as described respectively in 49 CFR 177.834 (i), (3), and (4)
  • Refueling tanks must be retested every 2 1/2 years in accordance with 49 CFR 180.352
  • Transfer Flow’s DOT Special Permit SP-11911 is supplied with every refueling tank, and must be carried aboard each vehicle using a refueling tank

Caution Information

Each Transfer Flow fuel system is accompanied by a complete set of instructions. These instructions must be followed with no exceptions. Always follow State and Federal guidelines for installation of fuel systems. The following requirements must be followed:

  • Do not weld or torch any fuel tank or fuel system component
  • Always check fuel lines for restrictions or kinks. A restriction or kink can result in either fuel returning to the wrong tank or loss of power when pulling heavy loads
  • Always use proper venting procedures (gas cap and/or rollover emissions valves) to prevent over pressurization of the tank
  • Never connect a hot wire with 12 volts directly to the sending unit as this will burn up the sending unit resistor
  • Never apply more than 3 psi to any Transfer Flow tank
  • Do not install fillnecks within 3 feet of any heat source or open flame
  • Do not install fuel lines within 3 inches of an exhaust system
  • Fuel lines should never be routed on the outside of the vehicle body
  • Transfer Flow fuel tanks are NEVER to be used in conjunction with fuel tanks made by other tank manufacturers

Failure to adhere to these requirements will invalidate all Transfer Flow warranties and responsibilities.

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