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HYDROSTATIC PRESSURE TESTS
Hydrostatic pressure tests are classified as follows:
1. DESTRUCTIVE TYPE
a. Burst test
b. Hold test
2. NON-DESTRUCTIVE TYPE
a. Proof pressure test
b. Change in length test (elongation or contraction)
c. Change in outside diameter or circumference test
d. Warp test
e. Rise test
f. Twist test
g. Kink test
h. Volumetric expansion test
Destructive Tests
Destructive tests are conducted on short specimens of hose,
normally 18 inches (460 mm) to 36 inches (915 mm) in length and,
as the name implies, the hose is destroyed in the performance of
the test.
a. Burst pressure is recorded as the pressure at which actual
rupture of a hose occurs.
b. A hold test, when required, is a means of determining
whether weakness will develop under a given pressure for
a specified period of time.
Non-Destructive Tests
Non-destructive tests are conducted on a full length of a hose or
hose assembly. These tests are for the purpose of eliminating hose
with defects which cannot be seen by visual examination or in order
to determine certain characteristics of the hose while it is under
internal pressure.
a. A proof pressure test is normally applied to hose for a
specified period of time. On new hose, the proof pressure is
usually 50% of the minimum specified burst except for
woven jacket fire hose where the proof pressure is twice
the service test pressure marked on the hose (67% of
specified minimum burst). Hydrostatic tests performed on
fire hose in service should be no higher than the service
test pressure referred to above. The regulation of these
pressures is extremely important so that no deteriorating
stresses will be applied, thus weakening a normal hose.
HOSE TESTING
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GENERAL INFORMATION
31
Product information is subject to change. For full details, visit our website or contact Customer Service.
SAFETY WARNING: Testing can be dangerous and should
be done only by trained personnel using proper tools and
procedures. Failure to follow such procedures might result
in damage to property and/or serious bodily injury.
The Rubber Manufacturers Association (RMA) recognizes, accepts
and recommends the testing methods of the American Society for
Testing and Materials (ASTM).
Unless otherwise specified, all hose tests are to be conducted in
accordance with ASTM Method No. D-380 (latest version). Where
an ASTM D-380 test is not available, another test method should be
selected and described in detail.
RMA participates with ASTM under the auspices of the American
National Standards Institute (ANSI) in Technical Committee 45
(TC45) of The International Organization for Standardization (ISO)
in developing both hose product and hose test method standards.
Many of the hose test method standards published by ISO duplicate
or closely parallel those shown in ASTM D-380. Many are unique
and, in those cases, the RMA may be able to provide the necessary
test standard references which may be purchased from the
American National Standards Institute (ANSI).
b. With some type of hose, it is useful to know how a hose will
act under pressure. All change in length tests, except when
performed on wire braid or wire spiralled hose, are made
with original length measurements taken under a pressure
of 10 psi (0.069 MPa). The specified pressure, which is
normally the proof pressure, is applied and immediate
measurement of the characteristics desired are taken
and recorded.
Percent length change (elongation or contraction) is the
difference between the length at 10 psi (0.069 MPa) (except
wire braided or wire spiralled) and that at the proof pressure
times 100 divided by the length at 10 psi (0.069 MPa).
Elongation occurs if the length of the hose under the proof
pressure is greater than at a pressure of 10 psi (0.069
MPa). Contraction occurs if the length at the proof pressure
is less than at 10 psi (0.069 MPa). In testing wire braided or
spiralled hose, the proof pressure is applied and the length
recorded. The pressure is then released and, at the end of
30 seconds, the length is measured; the measurement
obtained is termed the “original length.”
c. Percent change in outside diameter or circumference is the
difference between the outside diameter or circumference
at 10 psi (0.069 MPa) and that obtained under the proof
pressure times 100 divided by the outside diameter or
circumference at 10 psi (0.069 MPa). Expansion occurs if
the measurement at the proof pressure is greater than at
10 psi (0.069 MPa). Contraction occurs if the measurement
at the proof pressure is less than at 10 psi (0.069 MPa).
d. Warp is the deviation from a straight line drawn from fitting
to fitting; the maximum deviation from this line is warp. First,
a measurement is taken at 10 psi (0.069 MPa) and then
again at the proof pressure. The difference between the
two, in inches, is the warp. Normally, this is a feature
measured on woven jacket fire hose only.
e. Rise is a measure of the height a hose rises from the
surface of the test table while under pressure. The
difference between the rise at 10 psi (0.069 MPa) and at
the proof pressure is reported to the nearest 0.25 inch
(6.4 mm). Normally, this is a feature measured on woven
jacket fire hose only.
f. Twist is a rotation of the free end of the hose while under
pressure. A first reading is taken at 10 psi (0.069 MPa) and
a second reading at proof pressure. The difference, in
degrees, between the 10 psi (0.069 MPa) base and that at
the proof pressure is the twist. Twist is reported as right
twist (to tighten couplings) or left twist. Standing at the
pressure inlet and looking toward the free end of a hose,
a clockwise turning is right twist and counterclockwise is
left twist.
g. Kink test is a measure of the ability of woven jacket hose to
withstand a momentary pressure while the hose is bent
back sharply on itself at a point approximately 18 inches
(457 mm) from one end. Test is made at pressures ranging
from 62% of the proof pressure on sizes 3 inches (76 mm)
and 3.5 inches (89 mm) to 87% on sizes under 3 inches
(76 mm). This is a test applied to woven jacket fire hose only.
h. Volumetric expansion test is applicable only to specific
types of hose, such as hydraulic or power steering hose,
and is a measure of its volumetric expansion under ranges
of internal pressure.