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Skoda DVZ56 base fuze for Minengranate 28(t)

pzgr40

Well-Known Member
Premium Member
When you start collecting ammunition, everything is new and one is often amazed by the clever design features used in ammunition, either the way physical principals are applied……. The Germans call it an “Aha Erlebnis”, the Dutch and Enlish the ‘eureka’ moment when you finally understand the way something functions. However, the longer you collect, the more apart these moments –regretfully- become.

This time the eureka moment followed when studying a Tzech Skoda DVZ56 base fuze, used in the 15cm Minen granate 28(t). Somehow I was not able to figure out how the delay/non delay mechanim in the fuze worked, until I suddenly saw the light.

Description of the base fuze DVZ56:
The Skoda DVZ56 Base fuze is an impact fuze with an oponential delay function.
The fuze (pict.01 with numbers) consists of a two part steel body; in the lower part (1) the brass impact fuze (2), the delay mechanism (3) and the duplex detonator (4) are placed. On top of this steel lower body (1) the steel booster housing is screwed which ignites the main charge in the projectile body.
The brass impact fuze (pict.02) has a springloaded firing pin (5), retracted in a steel firing pin housing (6). The firing pin is kept in it’s springloaded position by two steel balls (7)which are placed on top of a flange at the base of the firing pin. These two steel balls (7) are kept in an inward position by a brass pipe which is connected to the brass base flange (8 ) of the fuze. A thin brass collar (9) with four outward pointing fingers at 90 degrees each fixate the inertia collar (10) placed above it in the upper position. A steel piston ring (11) is placed in a groove around the inertia collar. A strong spring (12) is placed under the inertia collar, pushing it upward. In top of the inertia collar six steel balls (13) are placed, axial and radially locked up. With these steel balls (13) locked in place, the firing pin housing (6) is not able to move forward.
A light compression spring (14) is placed on top of the firing pin housing (6) and ensures that some desceleration has to occur before the fuze is activated.

Upon firing the shell the inertia collar (10) rides the spring (12) downward, bending down the four fingers on the brass collar (9). The piston ring (11) expands as soon as it moves down into a wider part of the inside of the fuze body (2), preventing the inertia collar from returning upward. The six steel balls (13) are thrown outward by the centrifugal force, and start climbing the chamfered inside of the fuze body until they are thrown out of the brass fuze body (2) through two opposite slots and end up in the void of the steel fuze housing (1). The fuze is now fully armed. Upon impact the steel firing pin housing (6) moves forward, riding the the compression spring (14) untill the two steel balls (7) pass the end of the brass pipe (8) and are able to move outward, releasing the spring (15) loaded firing pin (5) into the firing cap (16).

The delay mechanism (pict.03) consists of a threaded brass housing in which two radial channels (17 & 18 ) are drilled, connected by a longitudal channel (19). In the upper radial channel (17) a springloaded pointed pin (20,red) is placed, the point placed in a groove of the inertia cilinder (21). The pin placed in the groove of the inertia cilinder keeps the pin in the afterward position far enough to close the central channel (22) through the delay mechanism housing.
Below the upper channel (17) a paralell lower channel (18 ) is drilled in which a steel ball (23) is placed. When the shell is fired and the steel ball (23) is placed under the inertia cilinder (21), the inertia cilinder is prevented from moving down, keeping the central channel (22) closed. If the fuze is rotated 180 degrees clockwise , the ball rolls to the other side of the channel (24), and the inertia cilinder can move down upon firing, allowing the spring in the pointed pin (20) to push the pin forward, opening the central channel (22).

90 degrees rotated from these two radial channels (17 & 18 ) , two longitudal holes are drilled (25) in which a pyrotechnic delay is pressed. If these are ignirted by the flame of the firing cap (16) it causes a 0,15 seconds delay in ignition of the duples detonator (4) above it.

In Pict.03 the green arrow shows the way the flame of the firing cap travels with non delay, the blue arrow shows the way the flame travels with delay.

The question remained however..... how to set delay or non delay. The awnser to that is -on hindsight- surprisingly simple. When assembling the fuze in the factory, a small indentation is made in the base of the flange of the fuze on the point where the ball in the lower channel is opposite (24) the inertia cylinder (21) -Pos 24 at six o’clock due to gravity- .
When the fuze is placed and tightened in the shell body this indentation is placed on the 6 o’çlock position, and an arrow pointing upward is painted on the 12 o’clock position at the base of the shell (Pict.04).
When ramming the shell in the barrel of the gun with the arrow pointing upward, the shell has no delay upon impact, ramming the shell into the barrel with the arrow pointing downward (Ball under inertia cilinder) gives the shell a 0,15 second delay upon impact, allowing it to pierce a target before exploding inside.
This mechanism is also found with Czech Skoda shells of 20cm and 30,5 cm.
The Germans calle it the “Ladepfeil” which can be translated as “loadingarrow”.

An ingenious and clever design…. those guys at Skoda really knew how to design ammo.

Dimensions of the fuze:

Diameter lower flange: 65mm
Diameter top part fuze: 50mm
Length of the fuze: 200mm

Regards, DJH
 

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  • Pict 02 - Base fuze DVZ56 detail.jpg
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  • Pict 03 - Base fuze DVZ56 delay mechanism.jpg
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  • Pict 04 - Base fuze DVZ56 for Minen granate 28t.jpg
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Excelent cutaway DJ.

The DVZ 56 is a Skoda factory designation.
The czech military designation for the fuze would be vz.28 (mark/model 28). However I have not seen a diagram or blueprint of the fuze vz. 28. There could be some changes.
In the collection of the Military University in Brno is a factory made cutaway marked D.Z.56 that looks exactly like DJ's.
Export models of the DVZ 56 could be tailored to the customers needs.
The DVZ 62 in the thread linked above is again Skoda factory designation of a later model.

To conclude this rant: It is highly probable that DVZ 56 is indeed vz. 28 fuze but i have no proof for this.

Bob
 

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