MIL-DTL-52031E
cylinder head connection shall be as shown in Figure 1. The cylinder with siphon tube installed shall
have an internal volume of 80 cubic inches, plus 2 cubic inches or minus 1 cubic inch, and shall have an
external diameter of 3.50 inches ± 0.06 inch.
3.4.1 Siphon tube. The fire extinguisher shall be fitted with a metal siphon tube located so that 90% of
the full charge shall be discharged when the extinguisher is held 45° to the horizontal with the valve and
discharge horn assembly facing upward. The siphon tube shall be attached in a leak proof manner by
threading, flaring, crimping, compression fitting, or copper flaring. A soft-soldered (sweated) connection
shall not be used. The siphon-tube attachment design and method will eliminate any possibility of leakage
at the siphon tube attachment point.
3.5 Cylinder-seal assembly. The cylinder-seal assembly shall be as shown in Figures 2, 3, and 4. The
seal-disk assembly shall be tightened to 25 foot-pound ± 1 foot-pound.
3.5.1 Seal disk. The seal disk shall burst at a pressure of 1050 psig ± 100 psig. The seal disk shall be
marked with the letters "FR" not exceeding 3/32 inch in height. When installed in the cylinder, some
portion of the "FR" marking shall be visible. The seal disk design shall not impede agent flow by partially
covering the puncture pin s bevel area flowing puncture of the disk
3.5.2 Cylinder-seal washer. The cylinder-seal washer shall be made from soft copper or nylon.
3.6 Cylinder-head assembly. The head assembly shall consist of a gasket, an internally threaded swivel
nut for attaching the assembly head to the cylinder, a valve with puncture pin, safety pin lock, hand grip,
swivel arm, nozzle orifice, and horn. Cylinder head assembly agent passageways shall be large enough
to assure unrestricted agent flow in the event cylinder debris from minor corrosion is present
3.6.1 Cylinder-head gasket. The gasket shall prevent leakage of the extinguisher contents between the
head assembly and the cylinder after the extinguisher handle is depressed. The gasket shall be such that
no leakage shall occur throughout the operating temperature range from -50° F to +120° F. The cylinder
head gasket material and design shall maintain its thickness and sealing capabilities for the duration of its
12 year product life despite repeated (twice annual) cylinder head removals for inspection and weighing
and repeated swiveling (see 3.6.2) of the head assembly on the cylinder. The gaskets thickness or
compressibility shall not be degraded by exposure to OE 30 lubricant or lifetime daily exposures to
temperatures of 185 ºF.
3.6.2 Threaded swivel nut. The swivel nut shall allow a full 360° rotation of the head assembly when
attached to the cylinder head to allow orientation of the head, relative to the cylinder before tightening.
The method of attaching the swivel nut to the valve assembly shall be the threaded fastener type.
Swagging or riveting is not acceptable.
3.6.3 Valve. The valve shall have a shutoff mechanism with a puncture pin. The puncture pin shall be
cut at angle and long enough to ensure proper penetration of the seal disk. When the cylinder head
assembly is secured on the cylinder, the puncture pin shall not puncture or make contact with the
frangible seal disk when the safety pin is pulled and the upper portion of the valve handle is depressed to
a point where the inner safety pin hole is completely blocked. To allow discharge in the event of the seal
disk rupture, the shutoff valve shall be held in a semi-open position when the safety pin is installed. The
valve-opening lever shall require an actuating force of not less than 8.25 pounds or more than 11 pounds
when measured approximately 1 inch from the end of the actuating handle. The valve-opening lever shall
be self-closing. After puncture of the seal disk and with the valve mechanism released, the valve shall
block the fire extinguisher discharge, and the assembly connections and seals shall not leak. The
puncture pins design will ensure unrestricted agent flow when the puncture pin penetrates the seal disk.
No part of the seal disk may cover or enter the end of the puncture pin.
3.6.4 Safety pin. The safety pin shall be fitted with a seal conforming to UL 299 for visually indicating the
removal of the safety pin. A chain attaching the safety pin to the head assembly shall be provided to
prevent removal or detachment of the safety pin. The safety pin shall easily fit into the handle valve body
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