Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Hi Maciek!
I guess the dimension fit pretty much in with the pipes in Simon's drawing.
Tore

[NZSnowman]

Hi Gents


I was able to find following information: the diameter of HP air piping leading to starting air flasks: internal - 36,5 mm, external - 44,5 mm.


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Regards
Maciek

Hi Maciek!
I guess the dimension fit pretty much in with the pipes in Simon's drawing.
Tore

Yes, it

[NZSnowman]

Tore, the line between the air compressor and the cross-over, what diameter do you think it is?

[tore]

Simon.
I am not sure  it is a line if you cannot see it on a photo. If you are able to confirm it visually then  I would guess the same as the 30 kg/cm2 pipe after the reducingvalve see picture below, it seems to be at least 20 mm. But this is one of the reasons I believe I`m in doubt of this pipe why should it be a direct 205 kg/cm2 connection directly without a reducingvalve to a 30 kg/cm2 system? That is quite a hazard, more over this pipe is not shown on the HP air diagram. The only reason I can think of is that it could be an emergency connection the other way eg. the startingair vessel used to supply air to the HPsystem in that case it would have been easier and safer to do it via the controlroom.
Tore

[tore]

Simon. I just checked the starting air system for the MAN engine. The direct line from the compressor shown on the diagram for the GW engine is not drawn in I guess my assumption is correct it is not such a connection. It would be completely  crazy. See the MAN system below, remember the MAN has a two stage reduction.
Tore

[tore]

Simon.
I have checked the various HP air system sketches  in my possession and except for the simple GW starting airsketch non of the others shows any direct connection between the compressors and the starting air crossoverline. As you see on the sketch below it is a 2nd connection from the compressors which is connected, (as I presumed) directly to the HP manifold in the controlroom and no connection to the crossover or the air starting system as the main HP line via a reducingvalve.
Tore

[SnakeDoc]

Hi


Just a thought, maybe the "starting air diagram for GW" (with additional, direct connection to the compressor) is the version for early boats (U93-U97) made by Krupp Yard, equipped with two electric compressors (similar issue as  Cooling-water system diagrams). The later boats (with GW and MAN engines) had one Junkers compressor (Luft Verdichter 1) and one electric driven compressor (Luft Verdichter 2). And in these boats, the direct connection was removed?


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Regards
Maciek

[tore]

Maciek-
An interesting idea, in that case the line would have to have a reducingvalve 205kg/cm2>30kg/cm2. Theoretically you could take a bleed off from the 2nd stage on the E-compressor ( appr. 30 kg/cm2), however on a freepiston compressor (Junker) I guess it would upset the balance which makes it impossible. If the 2nd connection to the control room is from the original design, including U92-97, which I believe, then I still fail to see why you should have a 3rd connection and not just a bleed off from the 2nd. pipe directly or rather via a reducingvalve in the engineroom to the crossover.
Tore

[SnakeDoc]

Or - other idea (inspired by Design Study of Former German Submarine  - Type IXC: "The starting air system supplies air for starting the main engines and the diesel air compressor. " http://uboatarchive.net/DesignStudiesTypeIXC.htm ) : this line exists only on boats with Junkers compressors (all type VIIC except U92-U97), because compressed air was used to start Junkers compressor (though I have always thought, that Ju-Verdichter was started manually).
Gents, in above mentioned report try use search for string "starting air" - maybe it tells something more...


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Regards
Maciek

[SnakeDoc]

compressed air was used to start Junkers compressor (though I have always thought, that Ju-Verdichter was started manually).

For starting up, compressed air is directed on the pistons brought into the outside position.

page 49, http://uboatarchive.net/U-570BritishReport.htm


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Regards
Maciek

[tore]

Maciek.
Brilliant! That`s it, we were fooled by  a sketch connection directly to the compressor assuming it was a supplyline from the compressor, forgetting the startingair to the Junker compressor which of course I shouldn't  have forgotten. Why was it different on the MAN system?  If you look at the system for the MAN engines, the crossover on the  system has a pressure of 75 kg/cm2 as the 2nd stage reduction of 75>30 kg/cm2 is on each separate engine thus you cannot use the crossover for starting air supply on the MAN system.On the MAN system the startingair for the Junker is taken from the ordinary HP supplyline of 205 kg/cm2 in the aft torpedoroom where it is connected to the Junker starting valve via an ordinary reductionvalve 205>30 kg/cm2.
 Simon, to make it simple: on the GW installations like U1308 and U 995 it is indeed a connection, presumably at least 20mm, from the crossover to the  startingvalve of the opposed piston Junker dieselcompressor which was installed on all VIICs after U 97. It is not a supply from the compressors. Thanks to Maciek.
Tore

[tore]

Simon-
Junker compressor startingsystem.
Further to my earlier post, the starting airpipe connection from the crossover to the Junker is via a compressor starting airvessel underneath the Junker. From this vessel the pipe goes to the starting valve at the center of the compressor as indicated on the bad photo below. I guess the size of the pipe from the crossover should not exceed 20 mm, rather smaller, as it is only a topping up line. The consumption for starting the compressor is taken from the starting airvessel. May be you are able to guess the dimension of the pipe by looking at the photo or better you shall find a good quality picture a U historia or may be from one of your exellent resources..
Tore

[NZSnowman]

Air Starting System


Fig. 1. Port Side.


Fig. 2. Starboard Side.


Fig. 3. Port and starboard Engine.

[tore]

Simon.
 It`s always a pleasure to see your drawings. As usual I have a few minor remarks. At the end of the fuelrack both stb. and port forward are endsprings enclosed in a steelsleeve, see picture.
Tore

[tore]

Simon.
Exhaust and inlet valve lubrication.
 I think it is a confusion here. In the British report from the inspection of the U 570 is mentioned that the cylinders are lubricated by luboilpipes inboard and outboard from the Gruetzner lubricators, further is mentioned that the inlet-and the exhaustvalves are lubricated by a camshaftdriven "mechanical pump".
Separate luboil connection to the cylinder liners is a very oldfashioned way of lubricating cylinderliners, in Germany during the years 1930-40 they were usually lubricated by the oil in the crankcase which is distributed and controlled in the cylinder by the pistonring arrangement. I cannot remember we had such a separate lubrication. I have not been able to locate any luboilpipes to the cylinderliners nor a "mechanical camshaftdriven luboilpump" which should take care of the valvelubrication except the Gruetzner lubricators having 12 pipeoutlets on each engine. In a way it is driven off the camshaft by a rod from the exhaust rockerarm on cyl 1. So if not somebody can explain and confirm the report of U 570 I`m inclined to skip the cylinder lubrication and let the Gruetzner take care of the valvestem lubrication.
Tore