the three units are dropped so that the
with each experimental charge. When a charge
longitudinal axis of the firing mechanism
produces satisfactory results, a series of at least
is perpendicular to the concrete at the
10 rounds is fired; 5 at -65F., and 5 at 200F.
instant of impact. The units should strike
If the performance at -65 and 200 F. is
the concrete at opposite ends of the
satisfactory, five cartridges are fired at -90 F.
The third unit is
to insure that the ignition system functions
dropped so that the axis of the firing
properly. When the locked-shut requirements
mechanism is parallel to the concrete at
are specified, a series of at least three firings is
the instant of impact.
conducted at 200 F. to determine that the
maximum pressure which the device may
Several special cartridges are fabricated
experience can be tolerated.
and used to evaluate wall strength. One
(3) If "no-load" requirements are given, a minimum
special cartridge should provide 150
of three rounds in the "no-load" condition must
percent of the maximum peak operational
be tested, and the parts inspected for rupture or
pressure. This cartridge is fired in a unit
after conditioning at 200 F., and the unit
dimensions may be checked against original
is inspected for deformation. A second
inspection records to determine if deformation
special cartridge is fabricated with
has taken place.
sufficient charge to produce 115 percent
generally are given with closed-system stroking
of the maximum locked-shut pressure
devices to insure that the body of the device will
obtained in the workhorse model tests.
retain the piston, tubes, cutter blade,. or gas
This cartridge is installed in a unit that is
pressure when the device is operated and
conditioned at 200 F., and the unit is
permitted to stroke without a restraining load.
fired locked shut. If rupture does not
occur, the unit is acceptable. When the
(4) The satisfactory completion of these firings
design does not permit the use of a
qualifies the device for prototype evaluation.
boosted charge, hydrostatic tests are
c. Prototype Evaluation.
submitted. In hydrostatic tests, a fluid is
pumped into the pressure chamber of the
conducted to insure that the performance of the
device at pressures comparable to those
heavy-duty workhorse models can be duplicated
obtained with the special cartridges. This
in a device that meets weight restrictions. Two
test is often used to test wall strength in
programs are conducted: structural and
A final structure test is necessary for
(2) Structural evaluation program.
thrusters and cutters required to withstand
(a) Structural evaluation includes tension,
These units are
compression, vibration, drop, wall-
conditioned at 200 F. and fired. The
strength, and leakage tests. The tension
devices are inspected for permanent
and compression tests are conducted at -
deformation or component failure.
65 70 and 200 F. with the device
The internal and external joints of the
mounted as it will be mounted in service.
device are tightened to the minimum
The maximum loads are applied and the
breakaway torque, as specified, and the
trunnions and initial and final locks are
assembled units are tested for leaks using
checked for permanent deformation or
the methods described previously under
the heading "Leak Detection."
(b) At least three units are vibrated in
If a failure occurs during the structural
accordance with Military Specifications.
tests, the deficiency must be corrected
Three units which have been vibrated are
before the program is resumed. The
dropped 6 feet onto a slab of reinforced
satisfactory completion of the structural
concrete. Two of
evaluation program qualifies