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Automatic Refueling Shutoff in Marine Vessels

Auto shutoff of a refueling nozzle is caused by fuel blocking the flow of air entering the nozzle’s aspirator hole near the end of the spout. Following is a list of factors that influence how that fuel gets to the aspirator hole. They all combine to cause fuel to back up the fill hose, causing the nozzle spout to be surrounded by fuel, activating the nozzle shutoff mechanism. Since changing any one of the factors can affect how the fuel in the fill hose responds, controlling all these factors is necessary to design a system that is consistently effective at preventing refueling spills, allowing room for expansion, and doing this without the premature shutoffs that often result when using valves to close the vent to cause automatic shutoff.

Factors that combine to cause auto shutoff of the fuel nozzle in current marine vessels

• Dispensing rate (varies from 4 GPM to 18GPM)
• Length of hose run (from 6” to 15’)
• Route of fill hose run (straight, 90 degree bends, horizontal, vertical)
• Height of fill fitting
• Height of vent fitting
• Allowing for ullage (every tank design is different)
• Number of times the consumer tries to top off the tank
• Preventing fuel from entering carbon canister - during filling and after expansion 
• Flex in the tank walls
• Shape of the tank top  (trapped air)
• Location of the vent in the tank
• Fuel/air separator
• Installation of the tank in the boat
• Carbon canister flow rate clean/saturated

Our testing has shown that as the carbon canister gets saturated tank pressures during filling increased. This pressure caused an increase of premature shutoffs in systems that worked satisfactorily with a clean canister.
An alternative to trying to balance all of the previous factors while fitting them into an existing boat configuration is to use Enviro-Fill’s Pressure Transfer Technology (patent pending) to reliably shut off the nozzle when the fuel in the tank reaches the desired level. Venting during refueling is through our integral vent system so a saturated canister has no effect on tank pressure during refilling.    

Factors that influence auto shutoff of the fuel nozzle with Enviro-Fill’s OPS

• Level of fuel in the tank