National Oilheat Research Alliance 27
• greater sensitivity to air ingress helps
identify slight leaks in the line or fittings
• reduced fuel degradation due to less
circulation of product
• reduced clogging of fuel filters and
pump strainers. One pipe systems move
over 90% less fuel through the fuel line,
filter and strainer than two pipe systems,
so filters and strainers last much longer
on one pipe systems
• cleaner combustion
Fuel line de-aerators
can be useful in converting
burners to one-pipe
systems as the fuel line
piping at the pump is not
changed and it continues
to operate with the
advantages offered by a
two pipe system
Supply Piping From the Top
vs. the Bottom of Tank
When the fuel lines are installed to connect
the AST to the burner, use of a one-pipe system
with the supply line piped to the tapping at
the tank bottom is recommended. When the
tank is installed with the proper pitch, this is
very useful for drawing off small amounts of
water that fall to the bottom of the tank. The
water is drawn into the line and then collected
(trapped) by the fuel filter.
When using the tank bottom tapping for the
fuel line connection, the installer should try to
position the shut off valve and line beneath the
tank to protect these components from possible
damage from instances such as objects falling
on the piping or people standing on the piping.
Fuel lines installed to connect the AST to the
burner can also be installed through a bushing
in the top of the tank. The system can be piped
in either a one-pipe configuration or a two-pipe
configuration, though the one-pipe system is
preferred. Outdoor ASTs are often connected
with the piping installed through the top of the
tank to prevent the impact of water accumulated
in the bottom of the tank, which can disrupt
the flow of fuel should the water freeze.
When using a two-pipe system, it is important
for the fuel return line to terminate at the
top of the tank to prevent a siphon effect should
a fitting or line leak occur. The fuel supply
line should terminate several inches above the
tank bottom. It is also important the fuel lines
be properly supported, secured and protected
from damage. Outdoor exposed lines should be
properly insulated.
When above ground tanks utilize piping
through a bushing at the top of the tank, it
is important the installer include provision
for both checking the tank for water and for
removing the water. If the tank does not have
a direct fill, a liquid-tight access for gauging
the tank may be considered. Additionally, the
tank bottom tapping should be configured to facilitate
draining the tank of accumulated water.
This could include use of a ‘freeze resistant’
Top draw line should be insulated on outdoor installation.
Line de-aerator