Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

By having the expansion tank pipe connected to the fuel oil venting pipe...  As soon as the tank is full of fuel oil, then the fuel oil will enter the expansion tank during refueling?


Regards,
Don_

[Don Prince]

Yes, the blue line through the selector valve does have the expansion tank connected to the sea in the fuel bunker configuration.  However, in the Ballast tank configuration the expansion tank is not connected to the sea other than through the open kingstons...


Regards,
Don_

[tore]

Don.
I guess we have a misunderstanding. On the image below I have marked a violet 1 for the ballast tank configuration, the selectorvalve is shut to the headertank and open to the sea. Seawater flows by a seapipe to the double seated selector valve and then to the small "expansion" tank, further by the bended (inverted U) pipe (shut drain cock) from the "expansion" tank into the ballasttank which then is in connection with the sea, thus acting as as "safety" line, relieving a possible excessive pressure in the ballast tank if the Kingstons are shut.
In the red circle marked fig 2 you have the system in fuelconfiguration having the selector valve shut  to the sea and open to the headertank, thus suppling compensating water at a pressure(head) from the headertank thru the "expansion" tank into the fueltank.
Tore

[Don Prince]

Hello Mr. Tore,


I see where you are correct as usual...  Could we compromise on the connection between the expansion tank and the fuel oil venting pipe.  See my attached drawing, or explain the reason for that connection.


Regards,
Don_

[Don Prince]

Hello again Mr. Tore,


I was thinking (Bad Don_ again)...  When the U-Boat is running on the surface with the saddle tanks in the fuel oil configuration, the internal and external pressure would be about 2 atmospheres. Water or fuel oil are not compressible. Let's say the U-Boat dives to 100 meters. Now, the external pressure is about 10 atmosphere and the saddle tank were sealed.  So the internal pressure is somewhat less than the external pressure I think???


Therefore, the expansion tank is open to the sea via the header tank and it provides the path for the saddle tanks pressure to equalize.  Since the liquids in the saddle tank are not compressible, perhaps the the expansion tank just applies the equalizing pressure (no expansion if any)...


Am I way wrong?


Regards,
Don_

[tore]

Don.
I guess you got it, and your fueloil venting ( draining) is workable, however the basics for my assumed design is the documentation available and Macieks reliable german source says: Verbunden ist dieser raum (expansiontank) mit dem bunker durch ein gebogenes Uebertrittsrohr an diesen hoeghster stelle ein entoelungsrohr angeschlossen ist. A bit freely translated:  the expansionbox is connected to the fueloil bunkertank by a bended overflowpipe which has a "deoiling" (oildrain) pipeconnection at the highest point. Hence the drain/venting connection on the top of the inverted U pipe. Macieks source could of course relate to an older design of VIICs but I guess we better stick to what is documented. We still lack an original image showing the arrangement.
Tore

[tore]

Hello again Mr. Tore,


I was thinking (Bad Don_ again)...  When the U-Boat is running on the surface with the saddle tanks in the fuel oil configuration, the internal and external pressure would be about 2 atmospheres. Water or fuel oil are not compressible. Let's say the U-Boat dives to 100 meters. Now, the external pressure is about 10 atmosphere and the saddle tank were sealed.  So the internal pressure is somewhat less than the external pressure I think???


Therefore, the expansion tank is open to the sea via the header tank and it provides the path for the saddle tanks pressure to equalize.  Since the liquids in the saddle tank are not compressible, perhaps the the expansion tank just applies the equalizing pressure (no expansion if any)...


Am I way wrong?


Regards,
Don_

Don.
When you are on the surface in fuelconfiguration the saddle tanks are via the selectorvalve in direct connection with the headertank and shut to the sea, Kingstons shut. Hence the pressure in the saddletanks is only that which is obtain by the head, hight of the headertank, above the saddletanks as for a normal fueltank. Submerged the pressure difference between the saddletanks and the sea shall still be only that of the headertank hight as the headertank is then connected to the sea by its overflowpipe as well as the swan neck on the top of the headertank.
Tore

[tore]

iquote author=Don Prince link=topic=921.msg19928#msg19928 date=1482005001]
By having the expansion tank pipe connected to the fuel oil venting pipe...  As soon as the tank is full of fuel oil, then the fuel oil will enter the expansion tank during refueling?


Regards,
Don_

When you are fueling, the fuel supply pressure forces the compensating water out of the saddletanks thru the compensating waterpipe, the compensating waterpipe ends about 10 cm above the residue water in the saddletanks. Close to the end of the fuelling you are all the time checking the compensating water outletflow from the testcock arrangement discussed. As soon as your testcock is showing fuel, you stop the filling. Possible fuelrests in the compensating watersystem is collected on the top of the inverted U pipe and "expansionbox" and can be drained later, when settled, by the test/draincocks. The headertank pipe ends in the bottom of the box,the possible fuel is on the top, thus you have a considerable, almost 1,5% of the tankvolume buffer to prevent fuel contamination of the compensating water system. This elaborate and complicated system has nothing to do with the environment people, they did not exist in the time of the VIICs, but at all cost to prevent an oilslick which might betray the submarines position.
Tore

[Don Prince]

Hello Mr. Tore,


You convinced me about the design of the expansion tank piping in the saddle tank...  However, the actual function of the expansion tank is another question?


In the fuel oil configuration mode; the expansion tank seems to do nothing.  When diving at depth equalization is done from the header tank through the expansion tank and to the venting pipe at the bottom of the saddle tank.


In the water ballast tank mode; if there was no expansion tank just a pipe at the bottom of the saddle tank, then in heavy seas the Kingstons could be exposed above the water line.  This action removes the header tank back pressure and may flush the header tank.  To eliminate the possibility of flushing the header tank, the expansion tank was added.  Therefore in heavy seas where the Kingstons were above the water line, the pipe to the expansion tank is exposed, but the water in the expansion tank maintains the header tank back pressure.


Is this a bad conclusion?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


Does this rendition look OK?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


I uploaded Skizzenbuch to dropbox with the updated version of page 83 on water compensating system and the selector valve.  When you have time would you please review page 83 and let me know in it is OK?


Regards,
Don_

[tore]

Don.
In fuelconfiguration the expansion box act as a possible oilspill buffer in the safety (relief) pipe to the sea, trapping possible fuel contaminated compensating water allowing to settle for a later drainage. As for your theory of while surfaced exposing the Kingstons to the surface  in heavy wheather I guess it is a bit far fetched. A list exposing the Kingston to the surface would possibly cause battery acidspill and should be avoided and a possible short drainage of the headertank would not cause much of a trouble as surfaced you top up the tank by the dieselcoolingwater continuously. I guess you should only maintain the purpose of the expansion tank would be to prevent oilcontaminating of the compensating water to prevent possible oilspill regardless of the reason.
I discovered there is a text mistake in my sketch  comp. water selector valve: The violet fig. 1 is fuelconfiguration and 2 is the ballast configuration as corrected on my image below.
Tore

[tore]

Don, I Guess so but may be you should add the selector valve in ballast position as well.
Tore

Hello Mr. Tore,


Does this rendition look OK?


Regards,
Don_

[SnakeDoc]

Hi Gentlemen,


because we do not have detailed documentation of the fuel compensating system, I have started searching any pieces of information related with this subject.
In the attached pdf file I have transcribed the description of the fueling process (in German). It is interesting itself, but also it can provide some clues regarding the fuel system. I did not translate it because I didn't want to make mis-interpretation. You can easily copy text and use some online translators. We can also discuss some parts of text here, on the forum.


I have also attached the drawing with the external fuel tanks and ballast/fuel tanks at the type IXC/40 U-Boat. In my opinion, especially interesting is the drawing of the fuel tank (Treibolbunker), whose piping is similar to the installation given by Tore. On the other side, the arrangement of the ballast/fuel tank (Tauchbunker) is simpler than the corresponding, hypothetical piping of the ballast/fuel tank at type VIIC U-Boat.


--
Regards
Maciek

[Don Prince]

Hello Mr. Tore,


I believe I have missed something with regards to the selector valve...  Does the selector valve have the header tank as its source and distributes compensating water to the saddle tank or to the sea (My drawing)? Or is the expansion tank the source and it is switched between the header tank or to the sea (Your drawing)?


1. In the ballast configuration you are shutting off all compensating water flow and the results would be an overflow at the header tank.


2. When surfacing, the ballast is blown to a point with compressed air, and then the diesel exhaust completes the blowing process.  It looks like there is a possibility for the expansion tank to get blown as well?


I thought we originally wanted the compensating water either going to the saddle tanks or to the sea?


However, your selector valve configuration makes sense where the compensating water flow stops at the saddle tank in the RFO Configuration, and stops at the selector valve in the water ballast configuration. 


Which is correct?


Regards,
Don_