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SELECTION, DESIGN & INSTALLATION
NOTES
Selection of the proper metal hose assembly for
any given application should take into account the following seven
considerations. They are known by the acronym STAMPED
S Size
of hose considering existing piping and flow requirements.
T Temperature
of media, hose and alloy ratings, temperature/pressure correction
factors.
A Type
of alloy (stainless, monel,
etc.) for proper corrosion resistance, temperature,
motion and pressure.
M
Motion and its frequency.
P Pressure-
constant, pulsing, shock.
E End
fittings- compatibility with medium and pressure.
D Developed
assembly length, live length and overall length.
There are many design concerns with respect to
metal hose. The following examples are merely representative of some
of these.
- In pulsating or shock applications, the assembly can have no
loose or slack braid after installation, or failure can
result.
- Unbraided assemblies should be used for vacuum or exhaust
applications only.
- Applications that involve axial compression or expansion
require the use of expansion joints, not corrugated metal hose
assemblies.
- Flow velocity can cause metal hose failure. If flow velocity
exceeds 150 ft/sec. for a gas or 75 ft/sec. for a liquid a metal
interlocked liner should be welded into the corrugated assembly
(100 ft/sec. gas and 50 ft/sec. liquid in unbraided assemblies).
If the assembly is to be installed in a bent position, reduce the
preceding values as follows: 50% for a 90 degree bend, 25% for a
45 degree bend, etc.. If velocity exceeds these figures match the
liner size to the conveying pipe size and use a larger metal hose
assembly.
- Motion definitions have been given in the glossary. Some
general rules for extending hose life in applications involving
motion are as follows: Vibration- for normal
vibration make sure the live length of the assembly matches what
is called for in the specification charts for vibration
applications. For strong vibration applications it is recommended
that Double Wall Hose be used. To calculate live length for
various classes of motion, use the formula shown at the end of
this section. Caution, corrugated metal hose
assemblies give no indication when their minimum bend radii are
being exceeded. In applications of mechanical motion proper design
can assure that minimum bend requirements are not being exceeded.
This is not the case in applications involving manual
handling.
- End fittings should be ordered with fluid compatibility and
pressure capacity in mind. Just because the hose, braid, and weld
of a 1/2" assembly can withstand 1425 psi operating pressure, if
the end fittings are only 150# female unions, the unions' maximum
pressure becomes the limiting factor for the entire
assembly.
- Torque, or twisting, of metal hose assemblies causes failure.
Care should be taken to avoid torquing the hose during
installation. The motions that an assembly is subjected to must
always be in the same plane.
- Never apply a wrench to weld collar or the braided hose
section of an assembly, as failure will occur, or at a minimum,
life expectancy will be reduced significantly.
- Use the proper length hose to avoid sharp bends or stresses.
Where these occur, use 90 degrees or 45 degrees fittings to
protect the assembly. Never compress an assembly to fit, as this
will loosen the braid and cause pressure failure. Never stretch an
assembly to fit as this will cause the cougations to wear against
the braid and cause failure.
- Avoid abrasion as failure can result from braid ends tearing.
Contact our office for various covers such as Spring Guards, Armor
Guards, Integral Rubber Covers, PVC covers, Fire Jackets, Fire
Sleeves, etc..
- Never use hose assemblies to support piping weight.
- Never exceed the recommended pressure rating of the assembly
as catastrophic failure can result.
- Clean hoses after use. Corrosive agents may solidify in
corrugations and cause failure.
- Store hose assemblies properly so that they are protected and
supported.
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