Author Topic: Tores mailbox VIIC and VIIC/41 operation and technical details  (Read 572671 times)

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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3585 on: 26 Mar , 2017, 02:50 »

Don.
You impression of the Germans used the pressure reducing valve d as a safetyvalve is probably based on a misunderstanding reading the pipescheme. As the drawn drainpipe from the valve looks rather big it is actually a very small drainpipe which by no means would be able to drain the system. It merely takes the small leakages from the ballancing bore in the reducing valve as can be seen on my image below.
Tore
« Last Edit: 26 Mar , 2017, 03:40 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3586 on: 26 Mar , 2017, 03:05 »
Hello Mr. Tore,


lets assume there is a plugged oil filter... If you are cranking the engine on air, then is there is no lube oil going to the engine. Would there be anything that notified the mechanic of this problem before the safety valve pops?  Would they ever get to the point of injecting fuel?


Regards,
Don_
« Last Edit: 26 Mar , 2017, 03:33 by Don Prince »
A man's got to know his limitations...
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3587 on: 26 Mar , 2017, 03:38 »
Don.
Humans can always overule the interlocks. You are able to crank the engine by air without luboilpressure as well as starting the engine without coolingwater etc. The fuel rack can be moved irrespective of the governor servo.  The system is based on qualified engineers operation and it is a limit as to how many interlocks you want to install and how much complications you  would introduce.
Tore
« Last Edit: 26 Mar , 2017, 03:43 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3588 on: 27 Mar , 2017, 02:42 »

Hello Mr. Tore,


For the GW diesel engine - would it be fair to say the safety valve works as follows:
1. The safety valve provides for high pressure relief seen at the lube oil pump head.
2. If the oil filter was getting plugged then the oil pump would see an increase in back pressure.
3. At some point the safety valve would reach the 'Cracking Point" where there would be a small flow of lube oil to the collection tank. The cracking point is generally far below the popping point.
4. If the oil filter problem continues to get worse, then at some point the safety valve will do a full vent flow or "Pop."
5. The pipe for the safety valve is not huge, but it should be large enough to create a pressure drop.
6. The safety valve is designed so that it will not recover from a full vent flow (Pop) until the pressure went down below the cracking point.
7. The lube oil pipe to the servomotor and the governor should sense the pressure drop and react by shutting down  the diesel engine.


The MAN diesel engine uses the safety valve to short the lube oil pump output to the lube oil input. I believe they are achieving the same result (a pressure drop). I have the schematics for the type IX U-Boat and the MAN 9 cylinder diesel engine and it does not have a reducing valve 1.5 < 3.0 atu in the lube oil system schematic.


I have done a lot of research on the safety valve...
 
If I assume the the GW 6 cylinder engine is at mid range rpm, then the attached lube oil pump pressure head is about 3 atu... Is that correct?


The reducing valve at 1.5 < 3 atu will create some back pressure when reducing its pressure output without an adequately sized vent line, but I guess the system can handle that back pressure with pipe lengths and passing through various components.


What do you think?


Kind regards,
Don_
« Last Edit: 27 Mar , 2017, 02:46 by Don Prince »
A man's got to know his limitations...
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3589 on: 27 Mar , 2017, 06:43 »

Don.
The attached lubeoilpump is of a gearwheel type meaning a positive displacement pump,  delivering a fixed volume pr. revolution. All such pumps for non compressible liquids require a safety valve to relieve the full max. volume to prevent damage in the event of fi. a shut discharge valve. As the pump is a positive displacement pump the safety valve has to open proportionally with the pressure. Generally such a safetyvalve is an integral part of the pump.
The servomotor of the governor forces the fuelrack to stop in the event of a pressuredrop below a preset minimum luboilpressure, irrespective of the cause.
Allthough they are drawn slightly diffent, there is in principle no difference between the GW and MAN systems. Below are the two systems, both system have an attached gearpump having a discharge pressure of 3 kg/cm2 and a reduction valve prior to the engine inlet to 1,5 kg/cm2. A branch off to the governor servo on the MAN engine is marked trieboelv.
Tore

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3590 on: 27 Mar , 2017, 20:14 »
Hello Mr. Tore,


Thank you for all your patients...  I have always tended to ask questions to gain a better understanding as to how things work (a personal flaw I guess)?


In order to access and change valve settings in the lube oil distribution valve chest, it looks like a center section of the floor panel must be raised. Was this section of the floor panel hinged for ease of access? Perhaps that shinny steel screwed down floor plate on U-995 is not original?

Also, when you are injecting anti-corrosion oil into the cooling water valve chest, I believe you would select each engine side separately.  Is that correct?

Regards,
Don_
« Last Edit: 27 Mar , 2017, 22:47 by Don Prince »
A man's got to know his limitations...
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3591 on: 28 Mar , 2017, 00:02 »
Don.
Don`t worry, I guess asking questions is an instrument for learning. The floorplatings were raised in the way of the lubeoil valvechest between the engines as you can see on my image below. The floorplatings have been changed on the museum U 995 as you can see and they differ from the original as shown on the top photo. I don`t think the platings were hinged.
You could flush the anticorrosion oil in many ways including each engine separately.
Tore
« Last Edit: 28 Mar , 2017, 00:45 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3592 on: 28 Mar , 2017, 19:18 »
Hello Mr. Tore,


I noticed something on your upper photo just posted...  Those pipes had the 3 band markings like the color bands on Plan 3. That would make it much easier to troubleshoot problems.  It looks like when U-995 was refurbished for the museum that the pipe color bands got painted over!


Regards,
Don_
A man's got to know his limitations...
Harry Callahan, SFPD

Offline NZSnowman

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3593 on: 28 Mar , 2017, 19:32 »
Hello Mr. Tore,


I noticed something on your upper photo just posted...  Those pipes had the 3 band markings like the color bands on Plan 3. That would make it much easier to troubleshoot problems.  It looks like when U-995 was refurbished for the museum that the pipe color bands got painted over!


Regards,
Don_

You are correct, most of the Colour Bands have be  painted over! There a few colours bands left in the Control Room also. It has taken me quite a while to figure out the correct colour band.

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3594 on: 29 Mar , 2017, 01:23 »

Don and Simon.
I guess the museum U 995 being short of funds are depending upon a lot of voluntary maintenance work, unfortunately a lot of painting is done without proper guidance. This result in overpainting items which sould not be painted at all. I guess the worst case is in the engine room which got red spot all over, blue valve pushrods which never was painted and the moving fuelrack including the HP fuelump rods which are ever moving items and  rather should have lubrication than a thick layor of glossy green paint.
Tore

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3595 on: 29 Mar , 2017, 02:28 »
Hello Mr. Tore and Simon,


The US Navy deck personnel (Swabbies) had an old saying "If it doesn't move, then paint it!" I guess the diesel engine wasn't running at the time... So, we now see what happened!!! Ha ha..


Regards,
Don_
A man's got to know his limitations...
Harry Callahan, SFPD

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3596 on: 29 Mar , 2017, 02:37 »
Hello Mr. Tore,


FYI... I did find a partial image of the Q Tank muffler.


Regards,
Don_



A man's got to know his limitations...
Harry Callahan, SFPD

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3597 on: 29 Mar , 2017, 04:37 »

Don.
Very good I guess we now have an image from two angles.
Tore

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3598 on: 29 Mar , 2017, 23:22 »
Hello Mr. Tore,


If a U-Boat makes a very deep dive and the pressure hull will then be compressed. Then, when the U-Boat resurfaces will the pressure hull stay compressed because there is no internal pressure to expand the pressure hull back to its original size?


If the pressure hull steel flexes inward between the round pressure frames, then I could visualize a return to the original displacement. However, as I look at U-995 there are some dimples here and there...


Regards,
Don_
A man's got to know his limitations...
Harry Callahan, SFPD

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3599 on: 30 Mar , 2017, 01:24 »

Don.
Normally the steel tensile strength of the pressurehull expands back to its original shape, however if the steel is subject to stresses exceeding the tensile strength you arrive into to the steel yield point and the steel begins to flow which means it would not retract to the original shape. The dents you see on the museum U 995 are primarily dents in the weaker part of the saddle tanks which migth derive from mooring collision. On some surface vessels hullplatings you migth see dents between the frames which might derive from weatherbeating or weldingstresses. If you see the pressurehull of a submarine you normally would`t  see such dents. A lot of modellers love to imply such dents, known as canning, I guess this is overdone particulary on the pressurehull.
Tore