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Terminology
Corrugated metal
hose allows for the transfer of liquids or gases, usually at high pressure
and high or cryogenic temperature while remaining flexible.
Corrugation
Design
Annular hose is formed from tubing into individual parallel corrugations.
Helical hose is also formed from tubing but into a continuous spiral
corrugation. Both designs allow for flexibility of the hose assembly under
pressure. In addition, helical hose has unique self-draining properties.
Pitch
Corrugated metal hose is normally manufactured in Standard Pitch
(Close Pitch). Each manufacturer specifies a standard number of corrugations
per foot based on their desire to provide for acceptable flexibility while
considering economic requirements.
Open Pitch
hose is also available and has fewer corrugations per foot. This hose
will not be as flexible as a Standard Pitch hose and will have a much
lower flexing cycle life. Open Pitch hose is intended to be used in less
severe applications where flexibility and cycle life are not an important
requirement or as an effective method for dampening vibration.
Superflex
allows OmegaFlex to achieve greater flexibility without thinning the wall
of the hose by increasing the number of corrugations per foot. Superflex
will normally have a higher flexing cycle life and can be used in more
severe applications where ease of flexibility is important.
Wall
Thickness
Each manufacturer designs a hose with criteria for the wall thickness
that considers flexibility, cycle life and corrosion resistance. Increasing
or decreasing the wall thickness has both advantages and disadvantages
to the user.
Metal wire braid on
a hose assembly provides the hose assembly a higher pressure capability
by acting as a restraint against hose elongation and acts to dampen vibration.
A second layer of braid may be used to increase pressure ratings provided
the test pressure is not exceeded which can result in permanent corrugation
deformation.
Other design considerations
may result in the use of a heavy braid to increase abrasion resistance
characteristics.
Braid
Coverage
Optimal braid coverage is engineered to contain the core under pressure
and reduce the possibility of squirm. Properly designed braid coverage
will balance pressure capability with flexing requirements. Minimization
of braid wear on the crown of the corrugation is also provided by optimal
braid coverage.
Tubular
Braid
Tubular Braid is manufactured by grouping single wires and then braiding
them into an intricate pattern that tightens when the braid is stretched.
The group of wires is also known as a strand.
Construction of the
braid is expressed as (number of carriers) x (number of wires in each
group) x (wire diameter). An example would be 24 x 8 x .012 where 24 is
the number of carriers on the braiding equipment, there are 8 wires in
each strand of wires and the diameter of each wire is .012".
Braided
Braid
Larger diameter hose assemblies require the strength of Braided Braid.
Braided braid is manufactured the same as tubular braid except that wires
in the strand are braided together prior to the manufacture of the braid.
Construction is expressed
the same as tubular braid except the use of parentheses around the groups
of wire and the wire diameter. An example would be 128 x (21 x .016) where
128 is the number of carriers, 21 is the number of wires in each group
and .016" is the diameter of each wire in the braid.
Braid Sleeve/Ferrule
The braid sleeve or
ferrule is used to isolate the end
of the corrugated hose and braid from flexure. The core and braid are
welded to the braid sleeve or ferrule during fabrication of the hose assembly.
Properties of the
hose and braid material are changed during welding. This area where the
properties are changed is known as the “heat-affected zone”.
The heat-affected zone must be isolated or premature failure of the hose
assembly can occur. Care should be taken to insure the braid sleeve or
ferrule has a proper fit.
Cover/Armor
The cover or armor
on a metal hose assembly is used to protect the braid from external abrasion
or to diffuse the media inside the hose in case of rupture. Many different
materials can be used including interlock casing, heat shrink covers,
lay-flat or many types of heavy-duty elastomers. The use of covers that
contain chlorides (such as PVC) should be avoided.
Reinforced Ends
Reinforced ends or
re-ends are recommended on applications where sharp bends or extreme flexure
occurs near the end of the hose. A short interlock casing or spring guard
is generally used to restrict bending.
Liner
Applications where
the media being transferred is abrasive or the velocity of the media is
above recommended levels require the use of a Liner.
Material for the liner is usually an interlock hose and it is welded to
each end of the hose. The liner will allow for a smooth flow while maintaining
hose flexibility and will reduce the inside diameter. The bend radius
of the interlock hose may limit the bend radius of the corrugated hose.
A directional flow arrow is normally provided on the outside of the hose
assembly.
| Specification Chart Headings |
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Hose Nominal Size
The nominal inside
diameter of the hose.
Number
of Braid Layers
Indicated the number of braid layers required to achieve the pressure
ratings listed.
Nominal
Outside Diameter
Nominal outside diameter of the hose or the hose and indicated number
of braid layers. This column is usually used to determine the proper braid
sleeve/ferrule or the cover dimensions.
Minimum
Centerline Bend Radius
The hose may be bent to a radius not less than the indicated amount without
permanent deformation. The type of flexing can be static or dynamic. Hose
in a static bend is in a non-moving application. The dynamic application
allows for random or intermittent flexing.
Pressure
Ratings
Pressure ratings are shown in three categories:
Maximum Rated Working
pressure is the maximum pressure the hose should be subjected to on a
continuous basis.
Maximum Rated Test
pressure is the maximum amount of pressure the hose can be subjected to
during testing without possible deformation of the hose corrugations.
Nominal Rated
Burst pressure is the pressure at which the hose assembly can be expected
to fail.
Safety Factor
of 4:1 is maintained by OmegaFlex on all published pressures.
Published pressures are shown in psig at 70°F. Reduction of pressure
ratings should be used by the proper application of temperature correction
factors. See Temperature
Correction Factors for more information.
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