long delay time switch No.9 & long delay time switch No.10 (time pencil)

[pzgr40]

Cutaway model of a British WW2 long delay switch No.9 in fired (left) and unfired (right) condition.
The switch is mainly used for igniting sabotage charges and was therefore mainly used by SOE and delivered to resistance groups.
The fuze consists of a brass tube (A) in which -from top to bottom- the housing for the lead break (B), the lead break (C), the firing pin (D), the firing pin spring (E), the lower spring tensioner (F) and the firing cap housing (G) are placed.
The dumbbel shaped lead break is in fact an alloy of Tellurium-lead that stretches uniformly until it breaks.
The diameter of the middle part of the dumbbel and the Tellurium-lead alloy percentages descide the time lapse until the lead dumbbel breaks. The dumbbel is connected to the housing for the lead break and the firing pin by means of two steel pins (H).

The pull spring is continiously pulling the firing pin downward trying to pull the firing pin into the firing cap. When the safety pin is placed the lower part of the U shape (where the tag is placed) sticks below the firing pin and blocks it from moving downward. As soon as the safety pin is removed the spring starts pulling down the firing pin and stretching the Tellurium-lead dumbbel until it breaks, activating the firing cap. Below the firing cap a sheet metal cage (J) is placed in which a length of fuze cord is placed. To the other side of the fuze cord the detonator is placed.
When looking at the lower side of both fuzes one can observe that with two equal fuzes the lower spring tensioner and the firing cap housing are at different heights. This can be explained as follows: to enshure the time between simmilar fuzes -3 hours for example- does not deviate more than a few percent, the firing pin is blocked by inserting the safety pin, and a threaded rod with a calibrated weight is screwed into the lower spring tensioner (hence it’s internal thread), which stretches it to a certrain length, so enshuring the pull force on the lead dumbbel is equal with all -3 hour- fuzes , regardless of the spring length or spring rate. The lower spring tensioner is fixated at this height, after which the firing cap housing is placed and fixated.

The fuze is available in the following time lapses: 1 hour, 6 hours, 12 hours, 24 hous, 3 days, 7 days, 14 days and 28 days. These values are at 65 degrees fahrenheit (18,3 degrees Celcius). Hotter temperatures will shorten the time delay, colder temperatures will lengthen the time delay.

Length (brass tube) : 94mm
Totale length ; plm 120mm
Diameter: 9.5mm

When destroying important targets it is adviced to use two time sitches per charge to avoid failure if one switch refuses to work.

 

[pzgr40]

The delay switch No.10 (time pencil) uses a 0,4mm iron wire that keeps the firing pin in a tensioned position. The fuze consists of a thin brass tube, housing a vial of Cupric cloride. Below that an intermediate piece is placed, connecting the brass tube with the firing pin housing, and keeping both liquid proof seperated. The firing pin housing houses the spring loaded firing pin, kept in tensioned position by the iron wire that runs upward along the vial, fixated in top of the housing by means of a screw. At both sides of the vial a small amout of cotton wool is placed which sucks up the cupric cloride and fixates the vial during transport.
The fuze is activated by pinching the thin brass tube with an plier, either standing upon the brass tube so the vial breaks, releasing the cupric chloride.
The following chemical reaction now occurs: CuCl[SUB]2[/SUB] + Fe → FeCl[SUB]2[/SUB] + Cu, in other words, the chloride replaces the copper with iron, eating away the wire until it breaks and releases the firing pin.
In the lower part of the fuze two inspection holes are drilled through which one can observe if the firing pin is still in tensioned position before using the fuze. A steel safety strip is placed between the two inspection holes. The colour of this strip indicates the delay time;
Black for 10 minutes, red for 30 minutes, white for 2 hours, green for 6 hours, yellow for 12 hours, and blue for 34 hours (blue is not tob e used below freezing point)

Regards, DJH

 

[MINENAZ16]

Hello DJH,
Nice, as always.
Thanks for sharing.
Maybe I missed something in your explanation but why No9 on your picture have different external length ?

 

[pzgr40]

Good moring, here it is:

"When looking at the lower side of both fuzes one can observe that with two equal fuzes the lower spring tensioner and the firing cap housing are at different heights. This can be explained as follows: to enshure the time between simmilar fuzes -3 hours for example- does not deviate more than a few percent, the firing pin is blocked by inserting the safety pin, and a threaded rod with a calibrated weight is screwed into the lower spring tensioner (hence it’s internal thread), which stretches it to a certrain length, so enshuring the pull force on the lead dumbbel is equal with all -3 hour- fuzes , regardless of the spring length or spring rate. The lower spring tensioner is fixated at this height, after which the firing cap housing is placed and fixated."

 

[Anders]

In the lower part of the fuze two inspection holes are drilled through which one can observe if the firing pin is still in tensioned position before using the fuze. A steel safety strip is placed between the two inspection holes. The colour of this strip indicates the delay time;
Black for 10 minutes, red for 30 minutes, white for 2 hours, green for 6 hours, yellow for 12 hours, and blue for 34 hours (blue is not tob e used below freezing point).

Nice cutaway, but I am pretty sure the Blue i 24 hours and not 34 hours.

 

[MINENAZ16]

Nice cutaway, but I am pretty sure the Blue i 24 hours and not 34 hours.

Us doc says 34h at 10°C and 24h at 15°C

 

[WWIIBuff]

I have a question regarding the Cupric Chloride inside the green vial of the Switch No.10. Am I correct that this chemical is only corrosive, and not explosive?

 

[millsbomber]

Yes it only decays the wire running through the spring

 

[WWIIBuff]

Thanks Dave!

 

[Anders]

Yes it only decays the wire running through the spring

Correct and I have written a piece about it here: https://timelapse.dk/timepencil.php

 

[WWIIBuff]

Thanks Anders! I did read your article before, and researched Copper Chloride, so I did not think it was explosive, but just wanted to be sure.

By the way, it is nice to see the pack of Blue time pencils you show in your article. I believe those are the rarest color to find. I am still looking for a pack of those. Plus yours are American made, which I think are even harder to find. :tinysmile_twink_t: