Rubber hydraulic hose and ... - Flipbook - Seite 310
Safety information | Danfoss
Analyzing failures
Analyzing failures
4. Symptom: The hose has burst,
but there is no indication of
multiple broken wires the entire
length of the hose. The hose
may have burst in more than one
place.
6. Symptom: Hose has burst on
the outside bend and appears to
be elliptical in the bent section.
In the case of a pump supply line,
the pump is noisy and very hot.
The exhaust line on the pump is
hard and brittle.
Cause: This would indicate that
the pressure has exceeded the
minimum burst strength of the
hose. Either a stronger hose is
needed or the hydraulic circuit has
a malfunction which is causing
unusually high pressure conditions.
Cause: Violation of the minimum
bend radius is most likely the
problem in both cases. Check
the minimum bend radius and
make sure that the application is
within specifications. In the case
of the pump supply line partial
collapse of the hose is causing the
pump to cavitate creating both
noise and heat. This is a most
serious situation and will result in
catastrophic pump failure if not
corrected.
5. Symptom: Hose has burst. An
examination indicates the wire
braid is rusted and the cover has
been cut, abraded or deteriorated
badly.
7. Symptom: Hose appears to be
flattened out in one or two areas
and appears to be kinked. It has
burst in this area and also appears
to be twisted.
Cause: The primary function
of the cover is to protect the
reinforcement. Elements that
may destroy or remove the hose
covers are:
1. Abrasion
2. Cutting
3. Battery acid
4. Steam cleaners
5. Chemical cleaning solutions
6. Muriatic acid (for cement cleanup)
7. Salt water
8. Heat
9. Extreme cold
Once the cover protection is
gone the wire reinforcement
is susceptible to attack from
moisture or other corrosive
matter.
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Cause: Torquing of a hydraulic
control hose will tear loose the
reinforcement layers and allow
the hose to burst through the
enlarged gaps between the
braided plaits of wire strands. Use
swivel fittings or joints to be sure
there is no twisting force on a
hydraulic hose.
8. Symptom: Hose type
has broken loose from the
reinforcement and piled up the
end of the hose. In some cases it
may protrude from the end of the
hose fitting.
Cause: The probable cause is
high vacuum or the wrong hose
for vacuum service. No vacuum
is recommended for double wire
braid, 4 and 6 spiral wire hose
unless some sort of internal coil
support is used. Even though a
hose is rated for vacuum service,
if it is kinked, flattened out or bent
too sharply this type of failure
may occur.
9. Symptom: Hose has burst
about six to eight inches away
from the end fitting. The wire
braid is rusted. There are no cuts
or abrasions of the outer cover.
Cause: Improper assembly
of the hose end fitting allowing
moisture to enter around the
edge of the fitting socket. The
moisture will wick through the
reinforcement. The heat generated
by the system will drive it out
around the fitting area but six
to eight inches away it will be
entrapped between the inner line
and outer cover causing corrosion
of the wire reinforcement.
10. Symptom: There are blisters
in the cover of the hose. If one
pricks the blisters, oil will be
found in them.
Cause: A minute pin hole
in the hose tube is allowing the
high pressure oil to seep between
it and the cover. Eventually it will
form a blister wherever the cover
adhesion is weakest. In the case
of a screw together reusable
fitting insufficient lubrication of
the hose and fitting can cause
this condition because the dry
tube will adhere to the rotating
nipple and tear enough to allow
seepage. Faulty hose can also
cause this condition.
12. Symptom: Fitting blew off of
the end of the hose.
Cause: It may be that the wrong
fitting has been put on the
hose. Recheck manufacturer’s
specifications and part numbers.
In the case of a crimped fitting
the wrong machine setting may
have been used resulting in over
or under crimping. The socket of a
screw together fitting for multiple
wire braided hose may be worn
beyond its tolerance. The swaging
dies in a swaged hose assembly
may be worn beyond the
manufacturer’s tolerances. The
fitting may have been applied
improperly to the hose. Check
manufacturer’s instructions. The
hose may have been installed
without leaving enough slack
to compensate for the possible
4% shortening that may occur
when the hose is pressurized. This
will impose a great force on the
fitting. The hose itself may be out
of tolerance.
13. Symptom: The tube of the
hose is badly deteriorated with
evidences of extreme swelling. In
some cases the hose tube may be
partially “washed out.”
11. Symptom: Blistering of the
hose cover where a gaseous fluid
is being used.
Cause: The high pressure gas
is effusing through the hose
tube, gathering under the cover
and eventually forming a blister
wherever the adhesion is weakest.
Specially constructed hoses are
available for high pressure gaseous
applications. Your supplier can
advise you on the proper hose to
use in these cases.
EMEA Danfoss rubber hydraulic hose, fitting, tooling and accessories category catalog
Cause: Indications are that the
hose tube is not compatible with
the agent being carried. Even
though the agent is normally
compatible, the addition of heat
can be the catalyst that can
cause inner liner deterioration.
Consult your hose supplier for
a compatibility list or present
him with a sample of the fluid
being conducted by the hose
for analysis. Make sure that the
operating temperatures both
internal and external do not
exceed recommendations.
14. Symptom: Hose has
burst. The hose cover is badly
deteriorated and the surface of
the rubber is crazed.
