Tores mailbox VIIC and VIIC/41 operation and technical details

[Katuna]

As to the hatch, it makes sense that it is the torpedo loading hatch now. It just seemed to me that it was located lower in the hull and wouldn't have been that visible when open. My mistake.


Tore, that overhead photo of the lifting bars is very interesting. Never realized that how they would rig the top end of the motor apart. Another question, where exactly were the engine spares carried? I know I had seen a photo somewhere (U-534 perhaps?) of a piston and a rod (?) that were stowed on the decking plates of the engine compartment. Would the area on top of the waste oil tank between the engines be used for storing spares crates? I would imagine, especially during the war, that spares would be crammed everywhere there was a cm to spare.

[tore]

Katuna, storage space for major engineparts was hard to find. I guess we found different places and volumes depending upon the mission of the sub. We usually operated along the long coastline of Norway and carried minimum of spareparts as we could get same by plane anytime. However when we took over our VIICs we found major large parts fixed to the pressurehull between the engines and the pressurehull as indicated on my image below. On U 995 I particulary remember a "barrel" containing a piston, the "barrel" was filled with conservation oil and fixed to the pressurehull in the engine room. For some reason I had to check this piston and opened the barrel putting my hand down to the piston. I was newly married and my weddingring slipped off the finger and disappeared down in the oil. Of course a disaster and with helping hands from my engineroom crew we were able to retrieve the ring at the bottom of the barrel after substansial work. Otherwise we got parts by plane fairly easy from our large storage ( called the Fox garden) in the submarine pen at Trondheim. Consumable parts like fuelinjectors, exhaustvalves etc were of course kept onboard. Otherwise you`ll find empty storage bins made by steel straps throughout the U 995 often used for hoses etc.
Tore

[Katuna]

I had noticed on U-995 that there are racks located on the pressure hull behind and slightly above each engine. I wondered if these were original or from its time in Norway. When you say "barrel", do you mean like a wooden barrel/keg or a metal canister? I love modeling little details like this but I want to get it correct. In the photo below, I'm assuming those are the stowage racks?

[tore]

Katuna, I can`t remember exactly, but I guess the pistoncontainer was made of steelplate and the lid secured by a steelring over a fold on the top. Barrel is a wrong word in this case. As to the stowage racks/bins I assume they were originals.
Tore

[Don Prince]

Hello Mr Tore,


The photo below shows the lubricating oil pump and housing with 12 lubricating lines to other locations on the GW Diesel engine where the oil pump just didn't provide the needed supply of lubrication oil. I see where there is an eye sight glass for viewing the housing's oil level. Was there an internal float level valve to assure an adequate Lubricating oil level?


Regards,
Don_

[tore]

Don.

The device on your image is called a lubricator which supply a calibrated oil droplet to various items on the engine. The system is common to most  large marine diesels. The device consist of a housing containing luboil ,the level is shown by a sight glass at the container.The working principle is that a camshaft is mechanical driven via a ratchet this camshaft operate several plunger pumps taking suction from the luboilcontainer inside the housing. Each plungerpump supply an adjustable droplet to the its lubrication point, this droplet is discharged to a waterfilled sightglass enabling you to check the supply. from the individual sightglasses is a small pipe leading to each individual lubrication point.  Below is an image showing a pipe to the exhaustvalve stem in the exhaustvalve casing.
Tore

[Don Prince]

Hello Mr. Tore,

"this droplet is discharged to a water filled sight glass enabling you to check the supply. From the individual sight glass is a small pipe leading to each individual lubricating point."

The sentence - "this droplet is discharged to a water filled sight glass enabling you to check the supply." How does this work?

It sounds like you are mixing oil and water?
See the image below... I found this on the internet, but I don't really understand what I'm looking at?

I assume you are seeing something inside the lubricator through the two rectangular windows in the front of the lubricator.  What is the purpose of the elongated window on the side of the lubricator?

Regards,
Don_

[Don Prince]

Hello Mr. Tore,


I found this on the internet... I don't fully understand it, so perhaps you can help???


Don_

[tore]

Don you have many systems to handle the distribution and counterpressure for lubricator as  your page for handling the steamcounterpressure for lubricators of the steamengines. You have similar system for cylinder lubrication of largebore marine diesels, however I guess the lubricator for the GW engine is a bit simpler. I never dismantled the GW lubricator and unfortunately I have no image of the lubricator as installed on the GW engine,  but I guess it works as follows: The plunger pump takes its oil from the oil oilchamber in the pumpcasing (the oillevel can be checked by the level glass in the lubricator casing) and discharge to the discharge sight glass filled with water kept in the glass by  springloaded inlet and dischargevalves. In the sightglass a certain volume of the  oil is permanently collected at the top of the sightglass due to a lesser specific weight of the oil than the water. As the oil is forced by the plunger in to the sight glass  it displaces the same volume of the oil on the top and this oilvolume is discharged through the discharge NR valve to the lubeoilpipe connecting the lubrication point. The sight glass checks the working of the lubrication and the volume discharged to the lubrication point, (permanent volume of the oil on top.)
Tore

[Katuna]

If I understand correctly, the sightglass on the forward end of the lubricator (the vertical glass) shows the level available in the lubricator reservoir itself. The feed to each oil pipe comes from the individual sightglasses located on the front (behind the two horizontal windows) and these glasses have water in them to a predetermined level. The oil floats on top of this and, as the feed to each lubrication point is increased or decreased, that level indication in the glass moves up or down.


I defer to the honorable Mr. Tore however as I'm taking a semi-educated guess.

[Don Prince]

Hello Mr. Tore and Katuna,

Question 1: What is the cylinder number for the cylinder closes to the maneuvering panel???
Question 2: The 12 hex head screws on lubricator, are they just for holding/attaching the lubrication lines???
Question 3: Where are the needle screw/valves to adjust the drop size to the sight glass located???

The last two posts look to be spot on as far as to how the "Lubricator" actually worked.

Another thought - the oil level in the sight glass tube would remain at a constant level because as the diesel engine speed increases or decreased, then the rocker arm drive would increase or decrease the number of oil drops provided to the sight glass tube and in turn provide more or less oil to the cylinder chamber through the non-return valve. The adjustment of the feed needle valve will increase or decrease the volume of the oil drop which results in more or less oil forced from the upper oil area of the sight glass and through the non-return valve providing more or less oil to the cylinder chamber. So, again the oil level at the top of the sight glass would remain at a constant level???

Perhaps the only way to change the oil level in the sight glass is to decrease the internal water level and the sight glass internal pressure will still be maintained (don't want to change the oil feed pressure). And another thought - why not just fill the sight glass with oil; that would still work for lubricating the cylinder chamber. However, Having water in the sight glass you can see the oil drop rising which is a visual verification that the Lubricator is working!

I have been doing some reading about marine Diesel engines on the internet. When the Diesel fuel oil ignites in the cylinder chamber sulfuric acid is created which will corrode the pistons, piston rings, cylinder sleeves, valves and valve seats, etc. The lubricator has 12 lubrication lines which go to the 6 cylinders on the GW Diesel engine (2 per cylinder). The cylinder lubrication oil has a special property (addictive) which neutralizes the sulphuric acid to counter the corrosion effect after ignition. If you look closely at the lubricator there is a large filler cap on the top. I believe when the oil level gets to be low, then it's the responsibility of the Diesel engine operator to refill the lubricator. This could be a normal scheduled maintenance procedure after a normal 4 hour shift.

Regards,
Don_

[tore]

Don and Katuna. I am afraid my post and assumption was not 100% clear and even uncorrect on some wordings. I guess it should be possible to find some details on the lubricator as the firm making the lubricators still exist. I guess the name is Gruetzner GMBH in Germany may be someone are able to retrieve some documents from the net. In spite of an old construction it might be some drawings exist. As to the lubrication points on the GW engine I can`t remember any cylinder lubrication, in fact as the GW engine is a trunk engine where you normally have a tendency to draw to much luboil up in the combustion chamber getting a too high luboil consumtion, hence the trunkengines have piston oilscraper rings scraping oil down to the sump. As far as my fragile memory goes the point lubrication were on the valve stems in the cylinder head, see my image below. In addition I am showing the filling lid on the lubricator which is manually topped up.
Tore

[Don Prince]

'Gruetzner GmbH has been a specialist in automatic lubrication systems since 1993. We find the optimal solution for your lubrication points. You save time, costs and increase the longevity of your machines. '

Your images - I could see one line going to the exhaust valve and one line going to the cylinder???

Could not have been them...
Don_

[Don Prince]

Hello Mr. Tore,

Here is where I was getting some info on Marine Diesel engine lubrication...
https://www.marineinsight.com/tech/ships-main-engine-lubrication-system-explained/

They have some great videos!
Regards,
Don_

[tore]

Don.

I had a quick look at the videos of the marine diesel, as far as I can see the videos are dealing with two stroke large bore marine diesels running on  heavy fuel, which often contains sulphur and in some cases residues from the fuelcracking and need special treatment. The GW engine is a four stroke medium speed trunk engine running on dieselfuel usually have a higher quality than heavy fuel , and mostly don`t require a cylinder lubrication as the piston and cylinderliner is in direct contact with the crankcase and system oil. A crosshead engine has a fixed pistonrod above the crankcase sealed from the crankcase by a packingbox around the pistonrod. After the packingbox is a conrod having a upperbearing in the crosshead and a lower (big end bearing on the crankshaft) in the crankcase.  This system usually requires a cylinderlubrication. The reason for having a crosshead is that you have a separate guide (crossheadshoe on a sliding face) which takes up the large sideforces in a special sliding component having a separate lubrication system.
Tore