at the forward end, except for the exit port. The exit
port is a small projection located along the longitudinal
axis of the device, having a standard flared tube fitting
Since the threads must be engaged by more than 0.08
The other end of the chamber has external threads for
inch to provide sufficient surface to meet torque,
connecting the cap.
vibration, and sealing requirements, the length of
b. The wall thickness necessary to contain the
engagement for strength is not the controlling factor.
maximum locked-shut pressure (estimated at 5,700 psi)
The length of engagement is made 0.4 inch to provide
may be found by using the curves of figure 23, sheet 1.
space for inserting Nylok pellets in the joint (para. 15).
The chamber is made of steel with a minimum yield
strength of 125,000 psi. The pressure ratio, therefore, is
a. The cap (fig. 81) serves both
to close the
chamber and to provide a mounting arrangement for the
assembled unit. Two lugs on the flat edge of the cap
provide space for mounting holes. The cap has two sets
of internal threads: a large one for attaching the cap to
Referring to the triaxial stress curve, the required wall
the chamber and a small one for attaching the firing-pin
ratio is found to be 1.044. Assuming that the outside
housing to the cap. A boss with a hole through it is
diameter is to be made 1 3/8 inches, the maximum
located on the outside face of the cap, and the initiator
inside diameter may be calculated as follows:
pin slides through this boss.
Since this size is based on the estimated locked-shut
pressure, and the actual pressure may exceed this
value, the wall thickness was doubled (0.068 inch). The
thickness of the bottom of the chamber where stress
concentrations are likely to occur was made
considerably larger than the wall thickness.
length of thread engagement necessary to contain the
locked-shut pressure may be found as follows:
Figure 81. Initiator cap.
b. Two safety-pin holes, perpendicular to each
other, pass through the boss so that a safety pin can be
placed through the firing pin to prevent accidental firing
of the device. Two holes are provided so the safety pin
may be inserted parallel to the mounting flange or
perpendicular to it.
90. Firing Mechanism . a. The mechanical firing
mechanism consists of a firing pin, initiator pin, locking
balls, and an initiator spring.
b. The firing pin (fig. 82)
is a short cylinder with
projection on its closed end which is designed to
protrude through an opening in the firing-pin housing to
† Safety factor.
‡ A 1.5 safety factor is included in this equation.