Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don.
May be we should refer to your photo of the exhaust manometer in the engine room starting at 0 being the atmospheric pressure, which is app. 10 meter watercolumn fresh water at 4 degrees C. Let us assume the submarine has been surfaced by HP air up to the top of the saddle tanks and that the salinity and temp. makes the seawater specific gravity like the freshwater (not 100% correct). That means we start blowing the saddletanks at a counterpressure of 0.22 mwc,  the counter pressure shall gradually be reduced as the boat raise. If you start exhaustblowing at MBT 3 you shall have a counterpressure of almost 5 mwc which means almost no water is forced out of the tank hence we blow that tank later. MBT 1 and 5 have less counter pressure than MBT 3 so we blow those tanks before 3 as the boat rise further. If we take all at the same time  only the saddletanks are blown the exhaust disappear via the saddletanks Kingstons.
Tore

[Don Prince]

Hello Mr. Tore,


Thanks for the info and drawing....  I got the drawing and info in by changing some wording and moved things around, but all in pages 164 through 166.  The latest Skizzenbuch was uploaded to dropbox...


Regards,
Don_

[tore]

Don.
 I checked your last Skizzenbook (2) on the exhaust blowing which is OK.
Tore

[tore]

Don.
On page 59 in your Skizzenbuch you have two photographs U 570 and U 995 to show two different fuel sample collectors. I am not sure if you have noticed an even more interesting difference on U 570 being commissioned 1941 there is no wheel for venting the bow buoyancy tank whereas U 995 being commissioned 1943 you have the ventwheel next to the ventwheel of MBT 5, in the controlroom see my picture. The explanation you`ll find on plate 28, the earlier version of VIICs had a local venting wheel in the forward torpedoroom as shown on my picture.
Tore

[Don Prince]

Hello Mr. Tore,


Interesting...  I have photos from a U-995 CD that shows two large hand-wheels above both the froward and aft pressure hull passage ways and 3 smaller ones above them. I assume one is for dive tank 1, and the others (?).


Regards,
Don_

[SnakeDoc]

Don,

I can see only two small hand-wheels above - these are hand-wheels for operating gate-valves of the ventilation ducts (located behind the bulkhead).

--
Regards
Maciek

[tore]

Don.
May be you remember the residue venting of aft MBT 2 being the other ventwheel. So where is the venting wheel of stern buoyancytank? Both version of the VII Cs have local venting of the stern buoyancy tank being a barhandle up front of the steeringgear. See the photo. Otherwise I agree with Maciek the other two wheels are for the ventilation ducts.

Tore

[SnakeDoc]

Tore,

May be you remember the residue venting of aft MBT 2 being the other ventwheel. So where is the venting wheel of stern buoyancytank? Both version of the VII Cs have local venting of the stern buoyancy tank being a barhandle up front of the steeringgear. See the photo. Otherwise I agree with Maciek the other two wheels are for the ventilation ducts.

Isn't this handle (marked as "stern buoyancy tank") of the Junkers compressor exhaust valve grinding gear?

--
Regards
Maciek

[SnakeDoc]

I have attached photos of the gate valves located behind aft control room bulkhead (two red wheels). The green wheel is the valve of the HP air bank 3 - which consists of two air flask located in the Petty Officers' Room.

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Regards
Maciek

[SnakeDoc]

Tore,

the hand wheel for the stern buoyancy tank should be located somewhere between 6th and 7th pressure hull frame - the same as the handle you have indicated.
I have attached close view of this handle - it seems quite strange for the vent valve - I think, it is manual drive for the diesel air-compressor exhaust valve grinding gear.

Anyway, I was not able to identify something else looking like the drive for the vent valve.

[SnakeDoc]

To make more confusion - here is the photo of the aft torpedo room of the U-570:



There are also two valves visible - a little different arrangement than on the U-995...

--
Regards
Maciek

[tore]

Maciek.
I remember we came to a conclusion that this handle would be the grinding (ratchet) for the Junker. When I was looking for the venting of the stern buoyancy tank I realised it was not operated from the control room and that the local rod for the pressurehull entrance was exactly where the we assumed the Junker grinding shaft was. I forgot about the interlock confusion. I still think it has to be the sternbuoyancy tankventing as there are no other indication for this venting. The confusing element is the interlock, it could be to prevent opening the stern tankventing while the Junker was running. The two stroke opposed freepiston balancing was very susceptible to exhaust backpressure. I`ll ponder a bit and revert.
Tore

[SnakeDoc]

I remember we came to a conclusion that this handle would be the grinding (ratchet) for the Junker. When I was looking for the venting of the stern buoyancy tank I realised it was not operated from the control room and that the local rod for the pressurehull entrance was exactly where the we assumed the Junker grinding shaft was. I forgot about the interlock confusion. I still think it has to be the sternbuoyancy tankventing as there are no other indication for this venting. The confusing element is the interlock, it could be to prevent opening the stern tankventing while the Junker was running. The two stroke opposed freepiston balancing was very susceptible to exhaust backpressure. I`ll ponder a bit and revert.

Tore, it is interesting. I think, you are right.

One note - on your drawing you are referring to the outer shell frames. I have marked (with green color) the pressure hull frames and the location of the valve.

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Regards
Maciek

[SnakeDoc]

From the British report on HMS Graph (ex U-570)

5.  In the case of the Junker's air compressor exhaust valve, the valve floats on the end of the main spindle.  It is rotated by an extension from the valve passing down the centre of the main spindle and is turned by hand.

I have also searched my archive materials and found following description referring to the Junkers compressor:

Die Störungen haben zumeist ihre Ursache darin, daß zu viel Schwallwasser in die Abgasleitung des Verdichters eintritt. Um die besonders bei Seegang auftretenden Anlaßschwierigkeiten zu beheben, ist z. Zt. (April 1941) eine Hilfsauspuffleitungen den Raum und auch eine Verbindungsleitung Stufe I Spülluft bei Alle Booten in Aussicht genommen. Bei einem Boot versuchsweise zwischen Abgasein- und austritt ein Wasserfänger eingebaut. Der Verdichter koonte bei geschickter Handhabung bis Seegang 5 angestellt und in Betrieb gehalten werden.

Not all is clear for me, but I would translate it as follows:

The damages are mostly caused by the fact that too much water enters the exhaust pipe of the compressor. To remove these difficulties encountered especially in rough seas, an auxiliary spaces in the exhaust line were introduced and also introduced the scavenging air line to stage I at all boats. One boat was experimentally fitted with the water-trap between beginning and ending of exhaust piping.The compressor can be skilfully operated up to the  sea state 5.

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Regards
Maciek

[tore]

Maciek.
Sorry about my drawing which I made in a hurry mixing the pressurehull framing with the outer hull thanks for correcting and Don don't`make use of my drawing, use Macieks green correction.
The German text indicate that they had trouble with water even entering the Junkers exhaust pipe, it seems they already in 1941 tried to make modifications. Of course the stern buoyancy tank was an important element in keeping the exhaust outlet up to prevent intrusion of water in the exhaustpipe increasing the risk of waterstroke, upsetting the balancing and the two stroke scavenging as well.
 I think we can make certain that the handle is the stern buoyancy tank venting handle converted from a conventional vent wheel to a 90 degrees turning handle with interlock preventing the Junker compressor to start ( exhaust valve to open) unless the stern buoyancy tank vent is shut, thereby keeping the stern up and exhaust pipe free from the seawater. I have made a sketch how I assume the interlock is working below.
Tore