Spiralling
out of control?
Often
the only option for hydraulic systems design engineers, spiral wire
hoses can be awkward to handle and pose many problems. But there is
a range that makes things easier for all concerned, says Marijke Luyssen
Hydraulic, spiral wire hose is not the easiest material from which to
make coupled hose assemblies. This is not only because it requires heavy-duty
crimpers and cutting machines, but mainly because it is usually very
rigid, heavy to handle and often requires specialist dual skiving. Due
to pressure requirements, however, spiral wire hose constructions are
often the only option for largebore pressure-delivery lines near the
hydraulic pump. These hoses are also recommended for high-impulse applications
such as hydrostatic transmissions. where there can frequently be very
high pressure peaks depending on how the equipment is operated. A spiral
arrangement of steel wire reinforcement over the inner tube for pressure
support will also withstand wire fatigue (from pressure peaks) and flexing
much better than steel wire arranged in a braided fashion. The spiral
arrangement also allows for a tighter pack of reinforcement strands
and therefore provides more complete coverage of the inner tube to better
contain high pressures. Gates has developed a global range of spiral
hoses and couplings that makes life that much easier for the off-highway
engineers, assemblers and the people on the production floor.
Spiral standards
Historically, both the US-based SAE organisation
and the European DIN Institute have developed standards for spiral wire-reinforced
hoses. The most common SAE J517 standards - 100R12, R13 and R l 5 -are
specified based on constant pressure lines: 28.0Mpa or 4,000psi for
the 100R12 standard (through l in). 35.0MPa or 5,000psi for the 100R13
and 42.0MPa or 6,000psi for the 100R15 standards. The DIN 20023 standard
- which has now been replaced by the European EN 856 standard - was
issued in 1978 specifying the 4SP type hose; the 4SH design being added
in 1987. Contrary to the SAE approach, the EN/DIN 4SP and 4SH standards
specify decreasing working pressures for increasing bore sizes that
are more aligned with hose manufacturers' production capabilities than
with the end-user's requirements. Figure 1 gives an overview of the
requirements of the most popular industry standards. The Global MegaSys
hose range from Gates is based on the constant pressure-line approach
of the SAE standards and features four pressure lines: 21.0MPa, 28.0Mpa,
35.0MPa and 42.0MPa. Each line comprises wire-braid (MxK) and spiral-wire
(GxK) hoses where the 'xK' denominates the pressure in '000psi' (Table
1) The idea behind the MegaSys hose range and the definition of the
pressure lines has been developed in close co-operation with some major
global OEMs. The MegaSys pressure lines have been identified as the
most common system pressure in the various hydraulic markets, allowing
design engineers to easily identify the most efficient hose construction
based on the system pressure of the machine.
....CONTD
