Titanic's Reciprocating Engines

Cian O'Reilly

Cian O'Reilly

Member
twins back together again...
 

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Mike Spooner

Mike Spooner

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Hi Cian,
In your research of the engine's details did you find any reason given for the choice of colour paint?
 
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Bill West

Member
Hi Cian, more great progress!

Regarding the throttle engine valve gear, I see that my Aspinall sketch didn't work out in 3D. My parts didn't align and so would twist under load. Here's another possible way to show how they work:
Bill
ThrtlEng2
 
Cian O'Reilly

Cian O'Reilly

Member
Hi Cian, more great progress!

Regarding the throttle engine valve gear, I see that my Aspinall sketch didn't work out in 3D. My parts didn't align and so would twist under load. Here's another possible way to show how they work:
BillView attachment 111082
Cheers Bill. nothing in that new drawing looks difficult to change. If you're satisfied with the config you've illustrated I'll get to it soon.
 
Cian O'Reilly

Cian O'Reilly

Member
Both engines running....

 
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Bill West

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Hi Cian. For the throttle engines I tried a few different designs, this fitted the engine drawings and made mechanical sense. It also makes it clear about how the governor motion lifts the cylinder valve and then the piston rod rises and resets it back to neutral. The opposite directions occur when the governor resets.

I wasn't able to find any hints at how H&W might have detailed the linkages and joints but at least this looks old fashioned. The 2 vertical links could have been twin bars with a spacer bolt midway, that helps the pivot joints. The bar coming up from the governor could have had a clevis on the end.

Go ahead with as little or as much detail as you like.

For the twin engine video.. WOW! That was busy little factory in there cranking out HP's at 21 knots. You've raised the bar on our ability to appreciate what the room looked and felt like. Thanks!

Bill
 
Cian O'Reilly

Cian O'Reilly

Member
Most photo's - if not all of them - of Olympic class reciprocating engines show them in the engine works in Belfast during test assembly and do not show them with the cylinders lagged for insulation. While it wasn't my intention originally to add this element to my build, I think it's interesting to see the difference the lagging casing makes to the appearance, so in these images I've added them to the Low Pressure Cylinders. Regarding colour, my understanding is that the casings were painted steel/light grey, possibly backed up by the Britannic's specification book. However, it has been suggested to me that they may have been painted red, similar to those on the Jeremiah O'Brien. So I'm showing them in both here. Opinions/thoughts welcome...
 

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Bill West

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Hi Cian I never wanted to mention the jackets because of the work already invested in detailing the castings but you are right that it is the way they appeared in the ship. The steam pipes may have been jacketed too although the big LP exhaust pipes are not particularly hot, only 100F.

For colour, I looked at pictures from my 2007 day cruise on the Jeremiah O'Brien and the jacket is silver not red. To me the red is just primer, the Britannic's grey looks more plausible.

Bill
 
Mike Spooner

Mike Spooner

Member
Good point the lack of lagging insulation and metal shield to hold the asbestos in place. As all steam pipes would have had.
 
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Bill West

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Hi Cian. I slowed the video settings down to watch the valve gear and noticed that at the moment the 4 sets are running in unison rather than in step with their own cylinder. I don't know easy it is to adjust the motion relationships in your software but this is something we went over on the old TRMA site. At that time I wrote out the motion for the cranks and valve eccentrics as follows.

On both engines, for forward the reverser handle is pushed outboard and the top of the crankshaft rotates to outboard, ie the same direction the handle moved. This also fits the engines having opposite rotation. The reverser's valve rod and piston rod will be moved downward and the eccentric links will be pushed outboard. The inboard eccentric rods will be the ones that are pushing on the valve stems.

The HP and IP cylinders are inside admission (steam supply is to the middle of the valve piston) and have crossed rods (the two eccentric rods look crossed when the crank is away from the piston). Looking at the engine drawings with the HP in forward I measured 52 degrees lag behind the crank for the eccentric whose rod is on the valve stem and 54.5 degrees lead for the other eccentric. I'll use the same as a guess for the IP.

The LP cylinders are outside admission and open rods but as a result have the eccentrics rotated 180 degrees. Continuing with my guess that makes the lag/valve stem eccentric 232 degrees behind the crank and the lead one 234.5 degrees ahead. In reverse the 54.5 and 234.5 degree lead eccentrics will be lagging and will be the ones pushing on the valve stems. Confused? me too!

The last bit is that in forward the lag/valve stem eccentric in each pair is the one that is away from the LP's and towards the HP or IP. They show on the drawings as being the ones whose rods are vertically straight, no offset. I think the object is to clear the bearings and couplings on the crankshaft without adding length. It also means that forward's dominance of the working hours pushes on the straight rod rather than the offset one.

The inside/outside admission and crossed/uncrossed rods are design decisions that one would not normally realize the designer had to consider but they do have a trickledown effect on finalizing the valve gear. It would be interesting to explore old texts about the advantages of each.

Back to our video, stick a protractor on the front end of the port crankshaft and set it so that a stationary pointer at the top touches zero degrees when the HP is on TDC. Use a protractor scale that has the numbers increasing CCW around the disk so that the degree reading increases as the crank progresses through a rotation. The protractor on the starboard engine will have a CW scale.

The degree events on the two protractors will then be (in order along the crankshaft, valve term valid for forward operation):
CrankAngles


The same events on the mirrored protractors means that the two cranks and their eccentrics are assembled with an opposite rotation of features around the shaft. I think that your having mirrored the engines will inherently accomplish this.

Bill
 
Cian O'Reilly

Cian O'Reilly

Member
Hi Cian. I slowed the video settings down to watch the valve gear and noticed that at the moment the 4 sets are running in unison rather than in step with their own cylinder. I don't know easy it is to adjust the motion relationships in your software but this is something we went over on the old TRMA site. At that time I wrote out the motion for the cranks and valve eccentrics as follows.

On both engines, for forward the reverser handle is pushed outboard and the top of the crankshaft rotates to outboard, ie the same direction the handle moved. This also fits the engines having opposite rotation. The reverser's valve rod and piston rod will be moved downward and the eccentric links will be pushed outboard. The inboard eccentric rods will be the ones that are pushing on the valve stems.

The HP and IP cylinders are inside admission (steam supply is to the middle of the valve piston) and have crossed rods (the two eccentric rods look crossed when the crank is away from the piston). Looking at the engine drawings with the HP in forward I measured 52 degrees lag behind the crank for the eccentric whose rod is on the valve stem and 54.5 degrees lead for the other eccentric. I'll use the same as a guess for the IP.

The LP cylinders are outside admission and open rods but as a result have the eccentrics rotated 180 degrees. Continuing with my guess that makes the lag/valve stem eccentric 232 degrees behind the crank and the lead one 234.5 degrees ahead. In reverse the 54.5 and 234.5 degree lead eccentrics will be lagging and will be the ones pushing on the valve stems. Confused? me too!

The last bit is that in forward the lag/valve stem eccentric in each pair is the one that is away from the LP's and towards the HP or IP. They show on the drawings as being the ones whose rods are vertically straight, no offset. I think the object is to clear the bearings and couplings on the crankshaft without adding length. It also means that forward's dominance of the working hours pushes on the straight rod rather than the offset one.

The inside/outside admission and crossed/uncrossed rods are design decisions that one would not normally realize the designer had to consider but they do have a trickledown effect on finalizing the valve gear. It would be interesting to explore old texts about the advantages of each.

Back to our video, stick a protractor on the front end of the port crankshaft and set it so that a stationary pointer at the top touches zero degrees when the HP is on TDC. Use a protractor scale that has the numbers increasing CCW around the disk so that the degree reading increases as the crank progresses through a rotation. The protractor on the starboard engine will have a CW scale.

The degree events on the two protractors will then be (in order along the crankshaft, valve term valid for forward operation):
View attachment 111144

The same events on the mirrored protractors means that the two cranks and their eccentrics are assembled with an opposite rotation of features around the shaft. I think that your having mirrored the engines will inherently accomplish this.

Bill
This is gold Bill, I've been wondering about exactly this for a while but wasn't sure if there was an issue. It definitely didn't sit right with me that the valve gear were working out of sync with the pistons. I'm at work now so I can't dig in to this but if you're willing I might ask for more help with this when I'm ready to tackle it?
Just to be clear...my aim with this is to be as accurate as possible and while I'm certain that errors have crept in over the course of the project and I've made outright mistakes I really do value correction when these issues are noticed, so thanks for this!
 
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Mike Spooner

Mike Spooner

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Whilst on the subject of reciprocating engines. One can see the world's biggest reciprocating (triple-expansion) working engine in steam this weekend 19th-20th November at Kempton Steam Museum near Heathrow airport UK. Which is the nearest to what was used in Titanic. As seen in DVDs documents This is the last steam up for this year. However, those can't make the visited information can be found on the website.
 
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Bill West

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Thank you for the compliment Cian. I'd be glad to help where I can. I could sketch out the angles graphically although the table is pretty clear. As a double acting engine the opposite of all these points are also relevant as power strokes or valve admission/exhaust points. Maybe that would overload a graphic diagram. Farther down the line I would like to diagram where the valve inlet and exhaust points occur to better appreciate the cutoff/expansion and the exhaust/cushioning stages. I'm hoping that the 3D video will make these valve motions evident. The valve admission is supposed to be about the first 1/2 of the piston stroke and the exhaust all but the last quarter or so of the exhaust side of the stroke. This makes the valve stem motions about a quarter of a revolution ahead of the piston rod motions. I've long wanted to easily see these steps in slow motion.

This conversation has also made me notice that as the IP is inside admission its exhaust is at the top and bottom of the valve chest. The LP's however as outside admission have their inlets at the top and bottom rather than the middle. This seems to fit perfectly with allowing the IP-LP pipes to be a simple horizontal pair, probably divides the flow down despite the increasing steam volume at that point and saves space too.

On the older style slide valves, outside admission has an advantage in that the steam pressure keeps the valve slide pressed against the seat but it does put higher pressure on the valve stem packing. Inside admission has the opposite benefits. Maybe the Olympic/Titanic's use of both piston and slide valves was handy in the inside/outside admission piping advantage.

Bill
 
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