they screw up and down so they can’t
vibrate open or closed accidentally, and they
permit adjustment for partial flow. Partial
flow, however, isn’t required for fuel shut-
offs. In my opinion, quarter-turn ball valves
are the hands-down best choice. They create
no restriction in the fuel flow. Further, the
position of their handle gives instant indica-
tion of whether they’re open or closed. An
added benefit: ball valves are relatively light
and compact. Cheaply made ball valves have
been known to vibrate themselves open or
closed, but well-made ones don’t engage in
such hijinks.Of course, you must make certain that
the fuel-line diameter and valve size meet
your engine manufacturer’s requirements—
the inlet port size on the engine. If the fuel-
supply run is very long or has numerous
bends and fittings, it’s a good idea to go up
one size to reduce friction.Remote Fuel Shutoffs
Neither ABYC nor CFR Yacht require remote
fuel shutoff valves outside the engine com-
partment. CFR Commercial and NFPA 302 do
require this. Frankly, I think remote fuel shut-
offs should be required on all boats over
28 feet (8.5 m) with inboard engines and
cabin accommodations. The reason is both
simple and frightening. The burning boat pic-
tured at the beginning of this chapter had all
the required fuel shutoff valves on the tanks.
It also had fire extinguishers on board. A
diesel fire like this is like a blowtorch, how-
ever. Cracking the engine hatches, the flames
were so intense that the fire extinguishers
were about as effective as spitting into aPART TWO:FUEL SYSTEMS
Figure 4-12.
Cutaway view of
an open ball valve
(Courtesy
Conbraco)
Estimating Fuel-Line Diameter
Diesel Engines
Best practice is alwaysto get the engine manufacturer’s recommendation for fuel-line diame-
ter, feed and return.Keep in mind that very long or complex fuel lines should go up a size in
diameter.There will be instances, however, when you need to estimate fuel-line size, and you
can use the following.Remember, err on the large size.You can always fit reducers, but you
can’t overcome the restriction of a pipe that is too small.The drawback to going too large is
the extra cost, greater space used, and added weight of bigger plumbing.These considera-
tions, too, are important, so don’t simply specify huge piping.
Small diesel engines use about^1 / 4 - inch NPT (DN 8 mm) pipe minimum for feed and return,
up to around 200 hp.
Diesels from 200 hp to about 350 hp use^3 / 8 - inch NPT (DN 10 mm) going to^1 / 2 in.
(DN 15 mm) at the upper end, feed and return.
Diesels from 350 hp to 650 hp use about^3 / 4 - inch NPT (DN 20 mm), feed and return.
Diesels from 650 hp to 1,200 hp use about 1-inch NPT (DN 25 mm), feed and return.
Again, the engine manufacturer should have the last word here.There is variation.For in-
stance, a CAT 300 hp engine specs^1 / 4 - inch (DN 8 mm) feed pipe andreturn, while a
GM 300 hp engine specs^3 / 8 - inch (DN 10 mm) feed and^1 / 4 - inch (DN 8 mm) return.Gasoline Engines
Gasoline engines range from^1 / 8 - inch (6 mm) pipe or tube (different sizes) for 10 hp or 12 hp
engines to^1 / 4 - inch NPT (DN 8 mm) pipe for 350 hp.Remember that many modern
fuel-injected gasoline engines also have return lines.Check with the engine manufacturer.