Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,


I have a question about grinding (burnishing) the exhaust flapper valve seat.  I have attached a photo from the uhistora web site.


Q1.  I assume this was dome to both exhaust valve seats?
Q2.  They state this was done every 4 to 6 hours?
Q3.  Item 4 in the photo - is this a lever/actuator to start the gringing process?
Q4.  Was there some type of electric motor connected to the shaft to rotate the flapper valve, or was it a motor connected by a machinist?
Q5.  The valve seat that was being burnished (remove carbon build-up) was it a type an lining similar to auto brake lining, metal to metal would not make a good water seal?


Regards,
Don_

[tore]

Don.
The group exhaustsystem consist of two flap valves, the inner which casing is shown on you photo and the outer being in a casing outside the pressure hull just before the silencer. Between these valves is a valve with the branch off to the exhaust blowsystem. The flapvalves have a valvedisc which can be rotated by means of a gearim on the disc which is connected to a wormgear. The inner flapvalve is operated by hand moving the rod seen on your photo, the outer is operated by a pneumatic motor which via rods and bevelgears rotates the wormgear on the outer flapvalve. The valve discs are rotated (in open state)once a watch to prevent carbon deposits on the rotating mechanism. When diving the valves are shut and rotated, thereby grinding the seatings which is conventional. If the valves were leaking we just waited till the water backpressure on the outer flapvalve was some 3-4 m wc giving a better pressure for the grinding. At depth greater the 5-6 m wc the resistance was too big for moving the disc. Between the two valves it is an ample drainage possibility to the bilge. I have tried to make some sketches of the system below.

[tore]

Don.
I believe something did go wrong with the first sketch so here is another try.
Tore

[Don Prince]

Hello Mr. Tore,


Since this was a manual job...  Was there a crank or a hand-wheel put on the shaft to grind the inner housing flap valve seat?


In your response...  What does "wc" stand for?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


a second question...  The photo from the Spanish site; can you identify items 6, 7, and 8.  Unless my Spanish-English translation really failed me.  I don't believe these items have anything to do with turbocharged gases or the control room.  I believe these lines and valves are on Plate 13 in the engine room...


I posted a part of Plate 13 where these line and valves look to be...


Regards,
Don_

[tore]

Hello Mr. Tore,


Since this was a manual job...  Was there a crank or a hand-wheel put on the shaft to grind the inner housing flap valve seat?


In your response...  What does "wc" stand for?


Regards,
Don_

Don.
WC stands for watercolumn in this case the pressure on the valvedisc caused by the seawater by the distance to the surface. I cannot remember excactly how the wheel / handle was I guess more like a bar.
Tore

[tore]

Hello Mr. Tore,


a second question...  The photo from the Spanish site; can you identify items 6, 7, and 8.  Unless my Spanish-English translation really failed me.  I don't believe these items have anything to do with turbocharged gases or the control room.  I believe these lines and valves are on Plate 13 in the engine room...


I posted a part of Plate 13 where these line and valves look to be...


Regards,
Don_

Don.
 I guess a part of your post has disappeared.
Tore

[tore]

Don.
Referring to your Spanish photo it is not a simple answer because I believe the Spanish explanation is a bit confusing and incomplete. The group exhaust boardcasing consist of several cast steel parts all having watercooled jackets. As these parts are flanged together the coolingwater has to bypass these flanges. This is done by coolingwater bends which you see on the photo. However the coolingwater has to flow for each flanged part: in at the lowest point and out at the highest, which make the piping a bit complicated. In addition to the cooling waterflow you have the main drain from the exhaustspace between the outer and inner group exhaustvalves, further ventingpipes and greasepipe for the valves. I think you have to study the coolingwater plate 13 to follow the flow. I have previously made a sketch trying to explain the system which is posted below. The group exhaust valve watercooled casing is in fact the main engine coolingwater overboard "pipe" as well and as such designed for full max divingpressure.
Tore

[VIC20]

Tore,


In the german original version of the manual I've found the sentence:



"Die Regelzellen sind angeschlossen an die Fluteinrichtung in der Zentrale…"


which means:


"The regulating tanks are connected to the flood installation in the command room"


But the english translation says:
"The regulating tanks are connected to the drainage installation in control room"


…in the description of the Torpedo compensating tanks Maciek used "drainage installation" for the word "Lenzleitung" which is correct (and the opposite of a "Fluteinrichtung")


Now when looking further into all the info about the different tanks I can't find out any info about how some of the tanks will be flooded (I mean where is the flood vent, where do they take the water from) - is it possible that there is such a flood installation with a common flood vent for the incoming water for these tanks?

- regulating tanks
- regulating reserve fuel oil tanks (when used as regulating tanks)
- Trim tanks (or do the trim tanks use a kind of closed system with a fixed amount of water to pump it around?)


Another question:
The torpedo compensating tanks… in the german version of the manual they write "Die Torpedozellen nehmen das Wasser für den Gewichtsausgleich der Torpedos und Minen sowie das Umhüllungswasser auf" - Maciek forgot to translate the word "Umhüllungswasser" in the english version: "The torpedo compensating tanks are flooded to compensate for the weight of a launched torpedo or mine." - this word is pretty tricky to translate it's like "surrounding water", I guess they mean the water used when flooding the torpedo tubes?


And one more question, how much time does it takes to blow the tanks with the diesel?
Rössler wrote in "U-Boottyp XXI" that it takes 2 minutes to blow the torpedo tubes with air (0.6 atm) - then blowing tanks with the diesel should take a lot of time right?

[tore]

Mark. I am not very conversant with the torpedosystem, I never interfered with the torpedo people. We have the same word "Umhullung" in Norwegian and I guess your assumption is correct, you flood the torpedotube, launch the torpedo, the surrounding water is ejected and you compensate for the totalweight torpedo plus surrounding water.
Exhaustblowing of the ballast tanks always seemed to me to take a long time. I Guess I never recorded the time and it varied depending upon trim, exhaustpressure adjusted by the outer flapvalve,weather and how much the ballasttank were blown by air etc.
Tore

[tore]

Mark.
Take a look at plate6 and you shall have a good understanding of the compensating, trim and regulating system. As you say most of the control of this system is situated in the controlroom. It is a very flexible system having its own seawaterconnection with volumecounter in the CR aft stb. Via a number of pipeconnection chests you can flood the tanks directly, or by connection to the bilge (Lenz) pumps. The regulating tanks (and Q tanks) have an inboard venting ending in a muffler down at the bilge, you can see the system with sightglasses clearly on the photos showing the aft part of the attack periscope casing in the aft controlroom. The use of drain in connection with the system is a bit confusing at least for the Europeans. In naval english we use more bilge and bilgepump (Lenzing) rather than drain, as we use drain in the meaning "tapfen".
The trimsystem is a bit different from the regulatingsystem as this is more like a pitching compensating rather than buoyancy compensating as done by the regulating tanks. thus you move the same water from fwd to aft or opposite. Although you have connections so you can adjust the amount of water you can play with.
Tore

[tore]

Mark.
Regulating tank flooding/filling. draining/ empytying.
Below is a a drawing of the floodinginstallation with connection to the various systems.
Tore

[VIC20]

Thank you! Could you give an estimation in minutes how long it took to blow the tanks with the diesel?

[tore]

Mark.
Exhaust gasblowing.
As I said the time could vary depending upon how much the tanks were emptied by air, the weather (sea), trim etc. Lets assume the exhaust pressure at the control panel in the controlroom is O,5 bar and the airblown tanks have placed the boat having casingdeck slightly above the sealevel, calm sea and a good trimlevel, thus ideal condition. My guess would be some 10-15 minutes. I never recorded the time so this is pure guesstimate from my side. In a difficult situation or very bad weather you always could sacrifice some HP air to shorten the time subject to the COs judgement.
Tore

[VIC20]

great, that helps a lot