The fuze (weight 15 oz. 12 dr.) is used in 8.8 cm and 10.5 cm H.E. A.A. shell and re-sembles the Zt.Z. S/30 in external appearance but differs in the mechanism in which the motive power is derived from centrifugal force instead of from a clock spring. The type is identified by the stamping "Zt.Z. S/30 Fg¹" around the side of the body above the flan-ge. The fuze is igniferous and has a maximum time of running of 30 seconds. The mecha-nism governing the setting is designed to prevent the fuze functioning at settings shorter than approximately 1 second.

The fuze consists of the base piece or body, the cap, the screwed collar and the me-chanism.

The base piece is screwthreaded externally below the flange for insertion in the shell and has a large cylindrical recess in which the mechanism is located. The recess is screw-threaded internally for the assembly of the screwed collar retaining the cap and has a flash hole and a number of holes for the retaining bolts of the mechanism in the base.

The cap is coned shaped with a rounded head and on a shoulder formed in its base ring carries the setting pin and the hammer spring. The steel pin is let into the base and en-gages an upturned forked strip on the setting disc of the mechanism. The hammer spring is secured to the shoulder in the base by two screws at one end and extends diametri-cally across the base of the cap. The unsupported end is forked to fit round the setting pin and is fitted with three brass hammer pieces on the underside. The two larger of these pieces are fitted one on each projection of the fork, i.e. each side of the setting pin, and the third smaller piece is nearer the centre of the spring. These positions coin-cide respectively with the projections on the fork end of the strip on the setting disc and a locking pin carried in the setting disc.

The screwed collar fitting over the lower portion of the cap has an internal rib held, with a waved wire tensioning spring, in a groove between the cap and its base ring.

The mechanism is assembled in a cylindrical unit of superimposed plates of brass and alu-minium and consists of:–

A central shaft with a spur near the lower end and a pinion at the base. The upper part of the shaft is reduced in diameter to receive the bush carrying the setting and safety discs and is screwthreaded to receive the tensioning and locking nuts. The sloping shoul-der forming by the reduction of the diameter is serrated to engage with similar serrations on the bush so that the bush is locked to the shaft. A stop pin on the pinion limits the rotational movement of the shaft.

Two weighted centrifugal toothed segments pivoted near the circumference of a circular plate and each enmeshed with a spur. The spurs carry pinions at their base ends which are enmeshed with the spur on the central shaft. The plate carrying the centrifugal seg-ments is cut away to provide clearance for the movement of the segments and the re-cesses thus formed are fitted with a spring strip which imparts the initial movement to the segment.

An escapement engaging the base pinion of the central shaft comprising three spurs with pinions and a spur with the escapement wheel. The wheel is engaged by two vertical arms on the pallet which is weighted at each end and controlled by a straight adjustable hair spring. The pallet is locked at one end by a centrifugal safety lever which is fitted with a weighting pin and held by a retaining spring. A step formed on the pivoted end of the lever is engaged by the end of the spring strip when the lever has swung to the ar-med position.

A disc assembly fitted at the upper end of the central shaft consists of a bush carrying two discs and a tensioning arrangement. The bush is in the form of a sleeve with a he-mispherical flange at the base. The sleeve position fits over the head of the central shaft and is serrated at the lower end to engage a corresponding shoulder on the shaft. The lower of the two discs, the safety disc, is keyed to the flange of the bush and so must always turn with the central shaft. The disc is smaller in diameter than the upper disc but has a projecting leaf formed at one part of its circumference to close a slot in the upper disc and so prevent the operation of the firing mechanism. The upper disc is the setting disc and is held on the sleeve of the bush under the tension of a saucer-shaped spring compressed and locked by two nuts on the central shaft. Before firing, the setting disc can be rotated relative to the bush and safety disc but after firing the discs are locked together when the locking pin carried in the setting disc is driven into the safety disc by the hammer spring. The setting disc has an upturned forked strip which engages the setting pin in the cap and, diametrically opposite, a curved slot which when aligned with a projection on the firing arm releases the firing mechanism.

The firing arm, operated by centrifugal force, consists of a shaft with a flat formed by a recess near its lower end and with a crosshead at its upper end. The crosshead has a weight attached to the underside at the end of one arm and a vertical strip projecting upwards from the end of the other arm. The strip bears against the edge of the setting disc and the lower end of the shaft obstructs the rotation of the retaining bolt.

The retaining bolt securing the retaining catch in contact with the detonator pellet is a centrifugal device held in the safe position by the shaft of the firing arm. The bolt con-sists of a short shaft with a radial arm attached at the head and a flat formed near the base. The radial arm engages the firing arm and provides the weight for centrifugal action whilst the flat engages the end of the flat side on the retaining catch.

The retaining catch in the form of a hook is pivoted at one end and hooked to engage the detonator pellet at the other.

The detonator pellet contained in a transverse rectangular slot in the base of the me-chanism unit is of brass and is rectangular in shape. A notch is cut in the two vertical sides and the detonator is contained in a recess at the inner end. A flash channel from this recess emerges at the underside of the pellet. A curved spring strip between the outer end of the pellet and one end of the pellet slot is held under compression by the retaining catch, engaging in one of the side recesses of the pellet. The needle is fixed in the opposite end of the slot. The detonator pellet is also held by a centrifugal safety catch.

The safety catch, located in a channel cut in the side of the pellet slot, consists of a flat brass plate shaped at its inner end to engage the front end and one side of the de-tonator pellet. The catch is retained in the safe position by a spring-loaded plunger with a rounded base which enters a recess in its surface.

The time of running is governed by the size of the arc extending clockwise between the curved slot in the setting disc and the position of the vertical projection on the cross-head of the firing arm. The fuze is set by turning the cap with the aid of a setting devi-ce. The rotation of the cap is transmitted to the setting disc by the setting pin engaging in the forked strip of the setting disc whilst the safety disc is held keyed to the statio-nary bush on the central shaft. The curved slot in the setting disc is thus rotated clear of the projecting leaf on the safety disc. The width of the leaf and its position relative to the vertical projection on the firing arm are so arranged that the leaf still closes the slot at settings up to approximately 1 second and so prevents the fuze functioning danger-ously near the gun.

On acceleration the hammer spring sets back flattening permanently the forked strip on the setting disc and thus disengaging it from the setting pin. At the same time the ham-mer spring strikes the small locking pin and drives it into an unsupported part of the safe-ty disc. The setting disc is then locked to the safety disc. When the safety lever has been thrown clear of the pellet by centrifugal force it is retained in this position by its spring engaging a step at its outer end. The toothed segments, operated initially by the springs fitted in the plate and subsequently by centrifugal force, then revolve the cen-tral shaft by means of the spurs and pinions. The disc assembly rotates with the shaft, the rate of rotation being controlled by the escapement. Whilst this movement is in pro-gress the weighted end of the crosshead on the firing arm is tending to swing outwards but is prevented from so doing by the upturned end bearing against the edge of the ro-tating setting disc. Also, the spring loaded plunger of the safety catch is eased from the catch by deceleration and the catch is thrown clear of the detonator pellet by centrifu-gal force.

When the slot in the setting disc reaches alignment with the upturned end of the cross-head the firing arm is revolved to the extent permitted by the slot and the recess cut in its lower part is turned to provide clearance for the arm of the retaining bolt. The arm then moves outwards and the flat surface on its shaft is rotated through a right angle so that it clears the side and the curved end of the retaining catch. The catch is then thrown clear of the detonator pellet which is driven on the needle by its spring.

Fig. 9