Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don.
I have started to look through you latest Skizzenbuch and it strikes me you are gradually going into more details of the VIICs which might require an upgrading of the prevous work done. While reading page 122 dealing with the engineroom exhaustsystem I guess the exhaustblowing of the ballasttanks has been a bit neglected. The outer main exhaustvalve has a task of being a damper,  operated by the engineroomcrew to adjust the exhaustback pressure of the dieselegine in operation. I have made an image on the subject. Kindly note that the outer exhaust system including the branch  to the exhaustblowingpanel is turned 90 degrees in relation to the inner system.
Tore

[Don Prince]

Hello Mr. Tore,


Thank you for taking the time and looking at the latest version.  I will be glad to make any changes that you deem necessary or should be changed. I know I have made many changes throughout the book form the discussions I had with you and Maciek. It always good to have a 2nd opinion by an expert! Also, I have made changes to the electronic documentation that Maciek provided (and we worked on) to get a more precise English wording. I sure hope that I have not made the info wrong or misleading.


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


The outer exhaust grinding system and muffled run horizontal above the pressure hull (I believe that is correct).  Does the 90 degree rotation mean this is related to the inner exhaust grinding system.  If I rotate the inner exhaust grinding system 90 degrees counter clockwise, then the exhaust pipe coming from the diesel engine would connect to the inner exhaust grinding system at the back side near the pressure hull? (that looks logical) But I need your advise on that???


I don't want to change the middle drawing to reflect the physical 90 degree turn because we would loose the clarity of the information presented. However, I will note the physical equipment relationship for accuracy.


What do you think?


Regards,
Don_

[tore]

Don.
I made the sketch showing the inner main exhaustvalve atwartship and outside the pressurehull, the exhaust flapvalve (damper) and  silencer alongship, thus turned 90 degrees, just to make it easier to understand the working. The exhaustdamper is primarerly used while exhaustblowing the ballasttanks.
Tore

[tore]

Don.
On page 143 of your Skizzenbuch I am afraid you have misunderstood the luboil system as you have connected the gravity drain from the main engine to the suctionside of the stb.attached lubeoilpump. I guess a description of the luboilsystem would clarify the matter.
The luboil system is based on two independent systems, for each engine, being able to  interconnect if needed. It works on a dry sump principle, meaning each engine have a separate systemtank under the engine. Below is an image of the normal and alternative operations. Normal operation of the port engine is as follows: the port systemtank holds the lubeoil for the port engine and the attached lubeoil pump takes its suction (green) via a normal NR footvalve in the tank. The discharge ( red having a reliefvalve with drain (blue) to the systemtank), goes to the distribution box between the engines passing a NR valve b. Valve a1 is open and allows the oil to flow via the main oilfilter with differentialmanometers to the port oilcooler having a dirty oil pipe(blue) via cock f to the port systemtank. After the cooler the oil passes a selector cock c1, in this case normally selecting the port engine. After that cock is a small pressureline to the servomotor for the governor on the camshaftdrive side (aft) of the engine. The servomotor shuts down the engine in case of lubeoilpressure failure and assists the governor in moving the fuelrack. The discharge pipe continues on the front of the engine to a pressure reductionvalve,( rembember the small red wheel?) reducing the pressure from 3kg/cm2 to 1,5 kg/cm2 before it branches off to the main bearings, camshaft drive and supercharger. When the lubeoil has passed the enginecomponents, gravity takes the oil through drainpipes (blue) to a selectionbox to port or stb systemtanks, where port in this case, normally is selected. The attached lubeoilpumps can not take suction via the drain system.
In case of an attached luboil pumpfailure, the quickest and easiest way of an alternative would be to use the aux. electric driven lubeoilpump. The system on my image is self explaning, I guess, and as a last alternative you are able to use the stb. attached lubeoil pump, which system you`ll find on my image as well.
Tore

[Don Prince]

Hello Mr. Tore,


I have a lot of work to do... I have a question about the Pneumatic Motors that drive the valve grinding for the external exhaust valves... Are the pneumatic motors started automatically when the hand wheel is turned to close the exhaust valve, or was some other action required to start the pneumatic motors?


Also, I don't believe I see any reference to the pneumatic motors on the mechanical or electrical German shizzenbuck PLATTs either?


Regards,
Don_

[tore]

Don.
The pneumatic grinding motors for the outer exhaust dampers were connected to the LP system as German plan 12 shows on my image below. There is no automatic starting, just  opening of the small LP air valves as shown. As prevously told, when diving, the dampers had to be fully shut and you experienced always some carbon deposits on the seatings. Our procedure was to start the grinding at some 3-4 meters to obtain sea backpressure on the valve disc for better grindingeffect. As the air used was released into the engine room, you had to limit the grinding as much as possible to prevent excessive overpressure in the submarine, buggering up the reading of the gauges.
Tore

[Don Prince]

Hello Mr. Tore,


The cooling water pump in in the aft e-room...  Was there a hardware setup that would permit anti-corrosion oil to be admitted into the seawater to the cooling blowers, e-motor bearings, thrust bearings, etc.?


By the way...  What does the abbreviation "NR" stand for in your write-up about the lubrication oil system?  "Normal" - something, I guess?


Why is there a return line through cock f to the collection tank? Would something be wrong with the oil cooler when using this line?


What is the big box the the left in the schematic? Is that the pump that is driven by a rocker arm that dispenses lube oil through small tubes to those hard to reach areas?


What is the function of valve g? and what is the return line directly ti the left of the pump for?


Regards,
Don_

[tore]

Don.
I don`t think there is an anticorrosion oil "infusion" in the E-room coolingwatersystem, however it is an anticorrosion connection at the stb engine groupexhaustvalve cooling system as indicated on the image below. The yellow line indicate the system entering the Junker compressor cooling water system. It is a possisbility to connect this system to the E-motors cooling systems shown by the broken yellow line as well as a more doubtful purple broken line to the e-compressor. The broken lines indicates I am not sure of these systems. Kindly note the E-room system is copied from the MAN coolingwater system as the plate 13 of the GW system is of bad quality. Both systems in the E room are the same.
NR stands for non return eg NR valve is a non return valve.
Cock f on the pipe from the lubeoilcooler is for draining the cooler, the pipe connects with the other draining pipes like safetyalve and reducing valves.
The rectangle on far left in the lubeoilsystem is the supercharger.
Tore

[tore]

Don.
I forgot your last question. Valve g and the small branch off pipe in this system is for lubeoil to the attached gearpump in those cases the pump do not work, but still is attached idling.
Tore

[tore]

Don.
The two drainlines in front of the engine is 1. the forward sumpdraining and 2. the draining of the pto lubrication of the attached equipment in the front of the engine.
Tore

[Don Prince]

Hello Mr. Tore,


Thank you for the info... There looks to be a 2nd thermometer and an oil pressure gauge on the oil pressure line after the oil cooled. Do you know their location? Photo?


Schematic attached...

Also, I have been reading about the difference between oil reducing valves and oil safety valves.
1. The reducing valve uses a spring and hand wheel to set the output pressure to a fixed value. However if the source pressure increases, then so does the output pressure.
2. The safety valve uses a spring and hand wheel to set the limit for its out pressure. If the source source pressure increased, then the excessive oil is drained off to hold the output pressure limit.


Valve h is definitely a safety valve (h          SICHERHEITSVENTIL )


Valve d is listed as a pressure reducing valve (d          DRUCKMINDERVENTIL)
 but has a drain line which makes me believe that the Germans were actually using a safety valve as a reducing valve - most likely to eliminate back pressure in the line.


What do you think?
Regards,
Don_

[tore]

Don.
The placing of the thermometers are indicated on the image below. Normally the temperature readings were done locally, except the cylinder exhausttemperatures, whereas the pressuregauges were assembled in an instrumentpanel for both engines placed high up between the engines, on the museums U 995 almost hidden behind a fluoroscent light tube. 
A pressurereducingvalve or more correctly pressurecontrol valve, is placed in the pipesystem to control the operating pressure in the system. The pressurecontrol valve is designed to open or shut to modulate or regulate the operating pressure. A pressure relief valve or safety valve is designed to open fully at a preset value and then shuts or resets when the pressure falls below the design maximun pressure. You should never used a pressure reducingvalve as a pressure reliefvalve to protect a structural integrity of a system.
Tore

[tore]

Don.
Below is a crossection image of a oilpressure reduction valve. As you see it is an intricate design with hydraulic ballancing bores having a drain.
Tore

[Don Prince]

Hello Mr. Tore,


OH!!! Then the pressure regulating valve is a double chambered valve with a drain...  very interesting! I was only reading about a single chambered regulating valve...


The safety valve attached to the oil pump's output...  The diesel engine's rpm will increase with speed. Therefore, the oil pump's pressure will increase as well.  This makes be believe that the oil pump cannot over pressurize the lube oil system and pop the safety valve. The only way to pop the safety valve is to have a valve shut that should be open for the lobe oil flow (a screw-up) or something got blocked like a filter or cooler.  Then the safety valve would pop and dump the oil back into its collection tank...


Am I making any sense?


Regards,
Don_