per hour (76 L/hr.) fuel would be consumed
and the remaining 40 gallons per hour
(151 L/hr.) would spill back to the day tank. A
150-gallon (568 L) day tank would be topped
off this way in 3 hours and 45 minutes.
Accordingly—in an emergency like this—the
crew would have to monitor the day-tank sta-
tus and switch to draw off it rather than off
the wing tank, when the day tank neared full.
Another alternative is to install two transfer
pumps in a switchable duplex arrangement.
In this case only a full electric outage would
require use of the bypass fuel lines, as it’s
highly unlikely that both transfer pumps
would go down at the same time.
The Common-Rail Manifold
The term manifold,as applied to piping, liter-
ally means many parts or many paths or chan-
nels. Any systematic collection of pipes for
directing fluid flow is a “manifold.” The
fuel-piping manifolds in Figures 4-6 and 4-7 are
typical examples. There is a specific type of pip-
ing manifold that can offer added benefits in
complex distribution systems. This is a piping
manifold in which the source or the return
branches from or into a single pipe. This single
pipe is called the “common rail” or sometimes
the “common bus.” Common-rail manifolds can
simplify and clarify distribution and control of
piping and allow for easy installation of built-in
spares for possible future equipment.
The day-tank piping schematic in
Figure 4-7 can be arranged with a common-
rail manifold on either the feed lines, on the
return lines, or both. This schematic—with a
common rail on both the feed and return
lines—is arranged as in Figure 4-8.
Note that a valve is still required right at
the tank takeoff, before the common rail.
Notice how a spare branch pipe (or several
spares) can easily be added to the common
rail.Chapter 4: Fuel Piping and Fuel System Bonding
Figure 4-8. Diesel
day-tank fuel pip-
ing with common-
rail manifolds