6/
20/
2006
6/
20/
2006
1
Fuel
Hose
Design
in
Fuel
Hose
Design
in
Relation
to
the
Design
and
Relation
to
the
Design
and
Operation
of
Handheld
Operation
of
Handheld
Power
Equipment
Power
Equipment
6/
21/
05
6/
21/
05
Design
Considerations
Design
Considerations
°
The
potential
for
fire
due
to
fuel
leakage
is
one
of
the
important
safety
concerns
of
HH­
products.
Fuel
hoses
are
an
important
part
of
the
hazard
analysis
of
every
product.

°
Engine
and
other
supporting
structure
vibrations
(
often
housing
the
fuel
tank
itself)
require
flexible
fuel
hoses
due
to
dynamic
elongation
during
engine
operation
(
often
the
engine/
carburetor
may
be
vibrating
or
displacing
in
a
different
mode
than
the
fuel
tank
itself).

 
Longer
lines
result
in
higher
permeation
areas
but
become
less
sensitive
to
bending/
torsion
as
the
forces
can
be
applied
over
greater
distances
 
Shorter
lines
reduce
exposure
to
permeation
but
increase
importance
of
material
properties
due
to
increases
in
dynamic
loads
and
reactions.
Design
Considerations
Design
Considerations
(
continued)

(
continued)

°
Space
and
weight
requirements
of
the
highly
integrated
handheld
products
determines
the
complex
geometry
of
the
fuel
hoses.

 
Increased
demands
to
reduce
weight
of
HH
products
to
improve
operator
comfort
and
safety
 
Increased
engine
complexity
from
exhaust
emission
requirements
has
added
weight
which
must
be
constantly
compensated
for
in
the
overall
design
°
Due
to
the
fact
that
conventional
extruded
fuel
lines
(
purchased
in
bulk
rolls)
are
much
lower
in
price,
the
industry
has
an
inherent
interest
in
not
using
complex
geometries.
Still
the
number
of
complex
geometries
has
increased
because
the
customer
wants
a
small
and
light
weight
product.
Examples
of
Complex
Examples
of
Complex
Geometries
Geometries
Trimmer
Trimmer
As
lines
become
shorter,
flexibility
is
more
important.
The
line
shape
must
be
modified
to
improve
flexibility
without
increasing
stress.
FEA
of
Torsion
and
Elongation
FEA
of
Torsion
and
Elongation
to
Optimize
Hose
Geometry
to
Optimize
Hose
Geometry
NBR
vs.
FKM
(
Considering
NBR
vs.
FKM
(
Considering
Machine
Design
Requirements)

Machine
Design
Requirements)

°
HH
products
must
be
capable
of
usage
in
environments
from
­
25
°
C
(­
15
°
F)
to
50
°
C
(
122
°
F).
Storage
temperatures
can
exceed
both
of
these
values.

 
NBR
shows
significant
advantages
at
low
temperatures
compared
to
FKM.
NBR
can
be
used
down
to
­
35
°
C
(­
31
°
F).
FKM
material
looses
much
of
its
flexibility
by
­
15
°
C
(+
5
°
F)

 
FKM
material
has
excellent
high
temperature
stability
°
Use
of
HH
machines
at
extremes
(
often
flexing
them
to
the
limits
of
AV
systems)
requires
material
to
be
high
in
tear
resistance
at
all
temperatures.

 
NBR
materials
show
a
higher
tear
resistance
compared
to
FKM.

°
Compared
to
FKM,
NBR
has
higher
wear­
stability
(
Less
likely
to
score
or
tear)
Partial
Crystallization
points
NBR
vs.
FKM
(
Considering
NBR
vs.
FKM
(
Considering
Machine
Design
Requirements)

Machine
Design
Requirements)

°
Fuel
hoses
may
be
used
to
connect
the
fuel
tank
(
at
one
side
of
the
anti­
vibration
system)
with
carburetor
(
at
the
other
side
of
the
AV
system).
Because
of
different
movements
at
the
connection
points
due
to
vibration,
elongation
properties
of
the
material
is
important.

 
The
elongation
of
NBR
is
better
as
compared
to
FKM
°
Due
to
the
material
characteristics,
more
complex
geometries
can
be
molded
using
NBR
compared
to
FKM.
Complex
geometries
are
needed
due
to
highly
integrated
engine
structures
and
the
tiny
remaining
space
for
fuel
hoses.

 
FKM
is
more
difficult
to
mold
into
complex
shapes
required
in
injection
molded
parts
°
The
price
of
FKM
parts
are
7­
10
times
higher
compared
to
NBR
parts.
For
complex
geometries,
the
tooling
costs
are
much
higher
and
demolding
is
critical.
NBR
vs.
FKM
(
Considering
NBR
vs.
FKM
(
Considering
Machine
Design
Requirements)

Machine
Design
Requirements)

°
Viton
(
FKM)
has
lower
permeability.

 
Better
from
a
regulator's
standpoint
°
Oxidation
and
deterioration
from
UV
are
important
factors
in
machine
design.
Lines
must
hold
up
for
the
product
life.

 
FKM
has
excellent
aging
stability
 
NBR
aging
stability
is
equally
stable
depending
on
the
additives
°
Exposure
to
fuels
and
lubricant
and
their
additives
requires
lines
to
be
chemically
resistive
 
FKM
has
excellent
media
stability
except
for
increased
swelling
from
oxygen
containing
compounds
such
as
aldehydes
and
alcohols
 
Industry
changed
fuel
lines
to
NBR
material
over
20
years
ago
to
improve
resistance
to
oxygenated
fuels
Proposal
to
EPA
from
the
HHPC
Proposal
to
EPA
from
the
HHPC
°
Due
to
the
environmental
and
design
considerations
of
HH­
products
the
use
of
NBR
for
short
fuel
hoses
is
recommended.

°
EPA
should
not
regulate
lines
less
than
6"
in
length
because:

 
Based
on
OPEI
HHPC
inventory
numbers,
lines
longer
than
6"
account
for
about
30%
of
the
products
 
Fuel
lines
need
material
properties
NBR
offers
 
Fuel
lines
require
higher
flexibility
which
cannot
be
obtained
from
FKM
at
all
temperatures
 
Emission
reduction
benefit
considering
all
fuel
lines
is
insignificant
compared
to
non­
road
SI
(
See
OPEI
data)

 
Cost
increases
7­
10
times
with
FKM
for
70%
of
the
products
