File:No82MkIIIT&PFuzeDiagram.jpg

Diagram of British No. 82 Mk III Time & Percussion Fuze, World War I era.
For use with shrapnel shells for QF 4.5 inch howitzer. Special design for use with low-velocity howitzers. The timer is started by its spin instead of by the shock of discharge, which was too low with the lower charges to reliably arm the fuze.
Timer burn time at rest is 40 seconds, which allows for the slower trajectory of a howitzer shell.
Body is of aluminium, similar to No. 80 Mk III, but is graduated from 0-40 rather than 0-22.
Action of timer :

• On initial discharge, the shearing wire in the safety pellet is broken, the pellet sits back and no longer retains the Bolt (see Y-Y Retaining Bolt).
• Shell rotation causes the centrigual force of Bolt to spin it outwards, and unlocks the other 2 bolts at right-angles to it (see section at Y-Y, Retaining Bolts in orange).
• The lighting pellet is no longer restrained, and centrifugal force causes it to spin out and drives its detonator onto the needle (see Y-Y, left side).
• The flash ignites the powder train in the rings, according to the time setting and ignites the pwder in the magazine.
• The flash from the magazine is transmitted through the shell, igniting the shrapnel bursing charge.

Action of percussion component :

• Before firing the safety pin is withdrawn, the closing pellet closes the pin hole.
• Shell rotation causes the Retaining Bolt near the base of fuze (in orange, right side) to spin out and free the percussion pellet.
• At this point only the Spring is restraining the Percussion Detonator Pellet.
• When the shell decelerates on striking any object, thew Percussion Pellet continues forward and impales the detonator pellet on to the needle.
• The flash ignites the magazine and hence causes the shell's bursting charge to fire the shrapnel bullets, as for the timer detonator.