The proper performance of a boat fuel system depends on the fuel tanks being correctly vented to the outside atmosphere. In most fuel systems, this is accomplished through use of a separate vent line that terminates in a thru-hull fitting located above the fuel tank.
Fuel Escaping From Vent Lines is an Environmental Problem
Venting a fuel tank allows fuel to flow freely to a boat’s fuel pump. It is also necessary to vent a tank to allow it to be filled with fuel. An analogy can be made to pouring from a can of chocolate syrup. Syrup will not flow freely from a can that has only had a single hole punched into it. Adding a second hole opposite of the first allows air to enter the can and the syrup will pour more easily.
The environmental problem with fuel vent lines is that up to a half a gallon of fuel can be spilled overboard during a typical refueling operation. Oil has a negative, cumulative effect on the marine environment, it’s expensive and boaters can face stiff penalties for inadvertently causing a fuel spill.
Spill Prevention Strategies for Fuel Vent Lines
There are several tactics that boaters can take to eliminate spills coming from fuel tank vents. A number of devices have been developed that use different strategies to keep the fuel in the tank. Among the options are fuel/air separators, audible warning devices, and fuel traps.
Fuel/Air Separators – These devices are installed inline with the vent hose at a high point above the fuel tank. They typically have a fuel flow diverter that diffuses fuel coming up the vent line and directs it back into the tank, while still allowing air to pass by the diverter. The separator is shaped to allow fuel vapors to condense on its interior surface and the coalesced fuel returns down the vent line to the tank. A good example of a fuel/air separator is the Racor LG100, which can be used in both diesel and gasoline based fuel systems.
Fuel Fill Warning Whistle – This simple device is spliced into the fuel tank vent line and as the tank is filled, the air displaced by the fuel produces a whistling sound. Once the fuel tank is full, the sound stops, warning the fueling operator to stop filling the tank. The 4-inch by 2-inch device is inexpensive, requires no maintenance and can be easily installed by a boater. West Marine sells one version of the warning whistle manufactured by Ocean Accessories LL for $33.99.
Fuel Vent Collector/Trap – This system uses a small high-density polyethylene container that is mounted by small suction cups over the fuel vent. Fuel coming out of the vent is physically captured in the plastic container. These collectors are inexpensive and work well on boats that have easily accessible fuel tank vents. Many owners place one of these devices over the fuel vent while their boat is left in storage for the winter. The Davis Instrument Company sells a fuel collector product called the No Spill Fuel Recovery System for $22.99.
Proper care of fuel tank vents and vent lines offer other benefits to boaters. Preventing vent line spills eliminates potential damage to vinyl striping and stained hull paint. Keeping the fuel vent clear and protected will help keep rainwater out of the fuel tank. Many prepared boaters will keep an oil absorbing pad handy to collect drips that could occur during fueling.
Alan Sorum - Alan Sorum is the Maritime Operations Project Manager for the Prince William Sound Regional Citizens' Advisory Council (PWSRCAC). Alan is ...
