Page 421 - Cat4800-Oct2011

407 Parker Industrial Hose Customer Service
866 810 HOSE (4673) 800 242 HOSE (4673)
Strongsville, OH South Gate, CA
Eastern USA Western USA
www.safehose.com
e-mail: indhose@parker.com
Safety & T
echnical Information
Force to Bend /
Minimum Bend Radius
Te amount of force required to bend a hose and the
minimum bend radius are important factors in hose
design and selection.Teminimumbend radius is defned
as the radius to which the hose can be bent in service
without damaging or appreciably shortening the life of the
product, and is measured to the inside of the curvature of
the bend. Te bend radius for a given application must be
equal to or greater than the rated minimum bend radius.
Bending the hose to a smaller bend radius than minimum
may kink the hose and result in premature failure.
Perhaps more important in determining fexibility, the
force-to-bend is defned as the amount of force required
to induce bending around a specifed radius. Te less force
that is required, the easier the product is tomaneuver in the
feld. Diferent hose constructions may require signifcantly
diferent forces to attain the same minimum bend radius.
Generally, the preferred hose is the more fexible hose,
provided all other properties are essentially equivalent.
Oil and Fuel Resistance
Rubber compounds are available in diferent formu­
lations, blends and grades. Compounds are selected by
hose design engineers based on the intended application
of the hose. For instance, a hose recommended for
multipurpose applications that may include hydraulic or
lubrication oil service generally contains a lower grade
of tube compound. Conversely, a hose recommended
for a more rigorous application, such as highly refned
fuel service, contains a higher grade of compound, often
within the same compound family.
Rubber hose is used to convey petroleum products both
in the crude and refned stages. Te aromatic content of
refned gasoline is often adjusted to control the octane
rating. Te presence of aromatic hydrocarbons in this fuel
generally has a greater efect on rubber components than
do aliphatic hydrocarbons. Aromatic materials in contact
with rubber tend to soften it and reduce its physical
properties. For long-lasting service, the purchaser of fuel
hose should inform the hosemanufacturer of the aromatic
content of the fuel to be handled so that the proper
tube compound can be recommended for the specifc
application.
Te efect of oil on rubber depends on a number of
factors that include the type of rubber compound, the
composition of the oil, the temperature and duration of
exposure. Rubber compounds can be classifed to their
degree of oil resistance based on their physical properties
after exposure to a standard test fuid. In this ARPM
classifcation, the rubber samples are immersed in IRM
903 oil at 212°F (100°C) for seventy hours. (See ASTM
Method D-471 for a detailed description of the oil and the
testing procedure.) As a guide to users of hose in contact
with oil, the oil resistance classes and a corresponding
description are listed on the next page.
Example:To make a 90° bend with 2" I.D. hose.
Given r = 4.5 inches.
General Formula for Minimum Hose Length
(given hose bend radius and degree of bend required)
.25 x 2 x 3.14 x 4.5 = 7" (minimum length
of hose to make bend
without damage to hose)
The minimum bend radius is measured to the inside
of the curvature.
Angle of Bend
360°
x 2 p r = Minimum length of hose to make bend.
r = Given bend radius of hose.
90
360° x 2 x 3.14 x 4.5
The bend radius for a given application must be equal to or
greater than the rated minimum bend radius. Bending the hose
to a smaller bend radius than minimum may kink the hose and
result in premature failure.
General Formula for Minimum Hose Length
(allowing relief from couplings)
Overall Length (OAL) = (2 x Length of Coupling) + (2 x Hose OD) + (Angle/360) x 2 p r