Description
The No. 28B is a pyrotechnic delay, aerial burst fuze, with possible time settings from 0-22 seconds, although 7 seconds is generally the minimum employed. The fuze consists of a body, an igniting mechanism, a fixed ring and setting ring, each containing a pyrotechnic delay element, a valve mechanism to prevent premature functioning of the fuze, and a magazine containing a gunpowder charge for igniting the photoflash or flare unit.
The fuze body has a flange, on the upper surface of which the fixed ring and the setting ring rest. Below the flange the body is externally threaded for insertion into the flash or flare. A securing ring screws onto these threads and locks the fuze in position.
A spring loaded detonator is housed in a chamber in the fuze body, opposite a fixed striker, and is held in position by the firing rod, movement of which is impeded by a springloaded ball engaging a groove in the rod. A flash channel extends from the detonator chamber to the delay element in the fixed ring.
The movable setting ring rests on a flange on the fuze body, and is placed below the fixed ring, which is secured by a screw to the fuze body. The delay elements are placed on the under surface of each ring in a circular groove, broken by a metal bridge. Communication between the grooves is effected by a hole in the top of the setting ring. An igniter pellet is placed in the upper end of this hole, and, when the fuze is set on safe, this pellet is masked by the bridge on the fixed ring. When the fuze is set live, the setting ring is moved to a position where its delay powder is above a flash pellet, located in a hole in the body. This hole communicates with a horizontal flash channel, which opens into a vertical flash channel. Freedom of movement of the setting ring is restricted by a tensioning ring, which is locked in position by fixing screws.
A spring loaded valve is located in the vertical flash channel, and is supported in a valve guide carried by a threaded arming-vane spindle. To the upper end of the spindle an armingvane collar, with vanes attached, is secured by a split pin. Rotation of the spindle is prevented by the firing rod, part of which is located in a groove in the arming-vane collar. A retaining plate prevents the spindle and the arming vane from being separated from the fuze. To prevent the valve from binding if the vane should be rotated downwards, a stop screw in the vane collar can engage with a similar screw in the retaining plate.
Two safety pins connected to a spring clip prevent movement of the spindle and the firing rod when they are in place.
This fuze is obsolescent, and is similar to early Fuzes No. 28 which are now obsolete. Although the fuzes are calibrated from 0-22 seconds, generally the numerals from 0 to 4 are painted out, and in some cases the numbers start at 4. In actual practice, no setting below 7 is authorized to be used, on account of the possibility of “blinds” or misfires.
Functioning
No information about functioning.
See Also
Nothing else to see.
Source(s)
OP 1665, British Explosive Ordnance (1946)
