sloping down about 5 degrees to drain. An
opening about 3 square inches (20 sq cm) is
in the baffle on the side away from the vent
inlet. The vent line then exits the top of the
tank—directly above the vent entry point be-
low but shielded by the baffle—and runs
overboard as usual. The baffle collects and
deflects bubbles and foam. The tank can ac-
cept both foam and bubble overflow, as well
as expansion overflow, simply returning the
excess by gravity to the main tank.Fill ’er Up
Standard fill pipes are nominal 1^1 / 2 - inch (DN
40 mm) pipe, with an ID of about 1^1 / 2 inches
(38 mm). On large yachts and commercial
vessels, use 2-inch (DN 50 mm) pipe. The fill
pipe should project down to within 1 inch
(25 mm) of the tank bottom for 1^1 / 2 - inch (DN
40 mm) pipe and to within 1^1 / 4 inches (DN
32 mm) for 2-inch (DN 50 mm) pipe—no
closer and not much higher. Effectively, this
seals the vapors in the fill pipe from the va-
pors in the tank (as long as there’s an inch or
more of fuel in the bottom). With gasoline
fuel, should a spark ignite the fill pipe vapors,
the flame can’t ignite the whole tank. You get,
hopefully, no more than an impressive but
relatively harmless bang. Extending the fill toChapter 5: Fuel Tanks and Fittings
Figure 5-6. Fuel/air separators (Courtesy
Racor)
Figure 5-7.
Cutaway view
of a Lifeguard
fuel/air separator
(Courtesy Racor)