111. Pressure-Release Antilifting Device SF 3 (Entlastungszünder Sofortzünder Metallfrei; SF 3)

a. Description. The pressure-releasing antilifting device SF 3 (fig. 137) consists of cylin-drical, bakelite case, about 3 inches high and 3 1/8 inches in diameter and contains very little metal. The case has a screw-on, disk-shaped bakelite lid containing a built-in fuze case. A flat, metal combination safety-and-arming bar, to which an arming cord is atta-ched, holds down the moveable, spring-loaded, striker-release disk. The fuze case con-tains a spring-loaded striker, a striker-retaining arm, a glass vial of chemical, a soluble pellet, and an arming spindle which is turned by the safety-and-arming bar to crush the vial of chemical when the antilifting device is to be armed. A rubber waterproof cap co-vers the fuze mechanism. The 7-ounce main charge is cylindrical and hollow, like a sec-tion of a pipe.

b. Employment. This pressure-release antilifting device is employed to activate mines and may be also as a booby trap.

c. Functioning. In the unarmed position the flat side of the arming spindle is against the glass vial of chemical. When the arming spindle is rotated 90° by the safety-and-arming bar it crushes the glass vial of chemical. The chemical the dissolves the safety pellet, which, with the projection on the under side of the striker-release disk, holds the striker-retaining arm in place. This takes from about 2 minutes (at 95° F.) to 40 minutes (at 31° F.). The antilifting device in now armed. The striker-retaining arm is now held in position only by the projection on the under side of the striker-release disk. When the weight is lifted from this antilifting device (fig. 138), the striker-relase disk rides upward under the force of the compressed release spring until the top of the striker-retaining arm is no lon-ger held in place by the projection on the under side of the striker-release disk. The spring-loaded striker then forces the bottom of the striker-retaining arm to tilt outward and is released against the percussion cap, firing the antilifting device.

d. Installing and Arming.

(1)

Before laying the antilifting device, loosen the arming cord from the lid to which it is fastened.

(2)

Then lay the antilifting device on a firm base in a deepened mine hole with the safety-and-arming bar pointing to the right, when facing the opposing force, and with the arming cord lying out to the rear.

(3)

Carefully press earth around the antilifting devicem by hand, keeping the top of the antilifting device clear and the safety-and-arming bar free to move.

(4)

Place the mine to be activated centrally on the top of the antilifting device.

(5)

Fill in the hole.

(6)

Pull lightly on the arming cord, rotating the safety-and-arming bar 90°. This cause the arming spindle to crush the glass vial of chemical, which arms the antilifting de-vice by dissolving the safety pellet.

e. Neutralizing. Once arming antilifting device cannot be neutralized. Destroy it and the activated mine in place. See also paragraph 109b.

f. Packing. Five of these pressure-release antilifting device are packed in a rectangular wooden box.

Figure 137. Pressure-release antilifting device SF 3.

Figure 138. Action of the pressure-release antilifting device SF 3
when weight is lifting.