SS Xantho John Penn trunk engine

[Stuart]

The counter balance on the lift arm ,springs on a loco was to reduce the effort required to lift the dead weight go the gear which in a 12 inch to the foot model would be large



Stuart

[PatJ]

I think the information says "counterbalance on the crankshaft and valve".

But a balanced valve is very different from a counterbalance on the valve gear, and it does not say "counterbalanced valve gear".

Hopefully Pedro can get some information out of the museum folks.

Rich Carlstedt said that the museum folks who had the Monitor were not necessarily up on their steam engines, and they reassembled the Monitor engine with some items in the wrong configuration, which Rich said he pointed out to them.
If the guys who made the drawings are still around, or if they knew what they were looking at when they drew the engine, then the museum should have some answers.

Pat J

[Jasonb]

As it says Crankshaft and Valve in the same sentence I would assume its weight balance as what else could it be on the crankshaft as that is not subject to steam pressure.

J

[Pedro]

It's an art in itself to write a technical article in language that is entirely unambiguous. My limited experience of technical journalists is that they can gloriously mangle the details of an interview and maybe that's what's happened here.
I'm new to valve gears but isn't the counterweight in the engraving for the Stephenson's link?
I've seen no evidence for that sort of counterweight on the Xantho engine itself. If there was one it would have been on the cross shaft running through eyes on the top of the frames.
The facebook side elevation photo on the first page of the thread shows what looks like a crosshead guide for the valve rod, which is missing on the engravings that we've seen so far of larger and slower engines. This would give useful support at the high speeds these motors ran.     

[PatJ]

I will have to look at the engravings and read the description again.
I read it rather hastily the other day.

I have noticed that not all technical books are necessarily correct on all points.
The knowledge of how steam engines workd was an evolving thing, and some books don't describe the suspension point of the link correctly for symmetrical valve operation, or even seem to be aware of such things, and just recommend suspending the link from the end, which is noted in some later literature as causing a lot of assemmetry in the valve movement throughout the range of the link motion.

For marine engines, this may not have been a problem since they generally ran in full link (correct term?), but I think the Xantos article mentions that link wear was a problem for this engine, and special inserts were used to accomodate the wear, but what this could say is that the suspension point was not laid out to minimize link slip.

Unfortunately some of the better steam books were heavy on the math, which can make for some daunting reading for some who don't have that background, or even for someone who does.

I have a book list, and a collection of PDF books.
I forget how many, perhaps 100 or so that I collected in the days when the PDF's could be downloaded for free.
I will post the list here somewhere if there is a place.
Edit: Posted here:
http://www.modelenginemaker.com/index.php/topic,3070.msg53149/topicseen.html#new

These are books in the public domain, and so they can be shared if someone has a method to transfer large files such as an FTP site.

Pat J

[peatoluser]

Thanks for the illustration of the balanced valve Pat, It explains the idea very clearly. like you I try to piece things together from reading the old books and looking at the illustrations, hopeing that there's no ytpo error!

my appologies about the matschoss links . I thought they would take you directly to the relevent sections.  you need to click 'erster band' then the page section.

given the stated speed of the engine and position of the valve on the side, I can see the reason for a balance weight as in your illustration that Jason pointed out - it looks to me as if it is trying to take some of the weight of the valve rod.

but also given the stated pressure, it would make sense to 'pressure balance' the valve. maybe both methods where used?

wearing out of bearing surfaces was a real problem, so counterweights were often used.

this was especially true of propellor shaft bearings.

HMS Royal Albert had to be run ashore to prevent her from sinking, because so much water was coming in through her stern tube, and on HMS Malacca it was recorded that the brass of the stern tube was wearing away at the rate of 5lb per day.

and perhaps to show that I've not entirely gone off topic, it was a certain John Penn in 1855 who largely solved the problem by using lignum vitae bearings.

Pedro, isn't there a full size replica of a John Penn trunk engine not far from you in 'Oil Fuel Hulk C77? (perhaps better known as HMS Warrior!)

yours

peter

[PatJ]

Peter-

I think the weight on the valve linkage is to balance the weight of the link and valve rods?

I am finding that there is a danger in talking in generalities about steam engines, since they evolved so dramatically in a short period of time.

Charles Porter mentions observing various engines at the London International Exhibition in 1862, where he displayed the first moder high-speed steam engine, but generally a slow speed steam engine does not have the rigourous design requirements that a high speed engine would have.
Almost any configuration can be made to work with a low speed engine, but that does not mean it is necessarily good design practice.

Porter noted that some engines were poorly designed with low efficiency, and furthermore, none of the engines displayed there were suitable for high speed operation (150-300 rpm) except his.  Porter also designed and demonstrated the first high speed governor with his engine at this exhibition.

The head of the Exhibition, Daniel Clark, forbid Porter from running his engine at a speed greater than 100 rpm, and even that speed was considered excessive.
Luckily Porter ignored Clark and ran his engine at 150 rpm, and demonstrated the first high speed steam engine.
When Porter first started his engine, it was widely though that the engine would fly into pieces.
Clark timed the engine with his watch, as a very nervous Porter watched, and after measuring 150 rpm, Clark turned to Porter and said "Mr. Porter, if you engine will run that smoothly, you can run it at any speed you want".

But there were a number of differences in the Porter engine, such as a very rigid frame, and shortened and enlarged crank pin, careful balancing, and other subtle but highly significant differneces, such as the piston not protruding into the port area.

So when you look in the old books, what you see depends on the era of the design, and the state of the art at that time.
Another thing to consider is that the illustrator (the guy making the engraving) did not necessarily understand engine design, and the engravings were not necessarily made to show the finer details of the engine, but rather an overall view of the appearance and workings of the engine.

Here is an engraving from Audel's, which shows a section of a relatively modern steam engine cylinder.
You can see the counterbore in each end of the cylinder, and you can also see that not only does the piston over-run the end of the cylinder, but more importantly the ring over-rides the bore, for it is the ring that actually does most of the wear on the cylinder.
And the piston does not protrude significantly into the passage area.

You can see the valve over-rides the valve seat in the engraving below also, and note that the cylinder heads are recessed inwards to minimize clearance and improve efficiency.

Studying the original drawings of a Dake engine show the same over-riding of the pistons against the back of the cylinder, with a groove used to accomplish this.

Pat J

[Pedro]

Hellsbells Pat, you are a mine of information. Thanks for the books too. Those clearances make so much sense (in hindsight) for a long life engine. What decade did that come from? Wikipedia says balanced valves were common in the US and rare in the UK, where piston valves were preferred. Trouble with a worn out piston valve I guess is it can't be easily fixed by a scraper hand. Still waiting for the ME to arrive and the curator to come off leave. 

Currently brooding on machining the cylinders. I think one end cover is cast in like in the engravings we've seen, so might need a separate valve plate to get the steam ports in. There are some awkward cast reinforcement webs too. Do you know if the cylinders would have been lagged, and if so with what? Lagging could cover a lot of sins......
     
Peter, I'd like to see Warrior, but considering her engine's a modern dummy, rightly or wrongly I feel I wouldn't learn much. Also her engine was of the old slow low pressure type, of which there's more info available. The Science museum has a model of HMS Minotaur's engine which had 112" bore, 52" stroke!

[PatJ]

Pedro-

When it comes to steam engines, yes, I admit, I am an obsessive compulsive.
I went through a period of research a few years back, and found a lot of steam engine information.

More recently I have focused on casting iron, and making workshop-type engines (sort of oversized models).

The restoration photos are low resolution but I think I can see heads on both sides of the engine, but at any rate that is how I would build it.
Trying to make the head built-in would be tricky, not impossible, but tricky.

Any way you make it will be interesting, and without museum plans, there is no way to be certain of exactly how it was.

Often times people free-lance engine designs to make an approximation of an engine, sometimes with some loss of accuracy, but with the benefit of having a reasonable design and build time and something that is not too complex to build.

I can see that the cylinders were cast separately, and then bolted together.
I would guess that the cylinders had lagging, that was somewhat typical of the old engines.
Generally strips of wood with insulation beneath, or just wood for the lagging; not critical for a model.

Are you aiming for a museum grade engine, or just looking for something to build?
You can go as wild as you want on detail, if you have the time and patience.

If you get the museum drawings, I would like to put the engine in a 3D model if that is possible to exchange that info.

Many choices to make.
I will be watching with interest.
Good luck.

Pat J

[Jasonb]

Yes it does look like the front cover is integral to the cylinder in the engineer engraving makes it a bit harder but not impossible. How did you intend to do the cylinders, machined from solid or fabricated?

The radial webs could easily be soldered into some shallow milled slots to locate them or if the engine is not going to run much on steam could be bonded on.

There is not much room for lagging but could well have been timber under a thin russian iron cladding sheet

J

[Pedro]

I'm fairly confident about the front cover being integral.  The Graces guide photo shows none of the cover bolts that you'd expect. I feel at present that redesigning it would cause more harm than good. On reflection, those webs and lugs are less of a problem than I first thought, but will still require a lot of care and some accurate sums. 

 Building something like this is outside my comfort zone so I'm really not sure how far to take it. My philosophy I suppose is to at least consider copying it as closely as my ability and patience allows and play to my strengths, then work on the weaknesses. If you build the bare bones as well as possible, at least you won't be kicking yourself later in the build.  I'm more used to carving from solid rather than fabrication, so that at least will be my starting point.  If I find that I'm really not up to the job, then is the time to simplify but  whatever happens I'm not prepared to compromise on the dimensions and the overall look of it, even though my primary goal is an elegant and smooth engine.
 
Of course if we can't get the drawings, a freelance element will be essential anyway.

 

[PatJ]

Pedro-

Look up some of JasonB's work if you are not already familiar with it.
He does a really good job of silver soldering up the bits into something that really looks like a casting, and like the original engine.

I hope you are good at silver soldering.

Pat J

[Jasonb]

You want webs

http://www.modelenginemaker.com/index.php/topic,705.msg10289.html#msg10289

J

PS spent too long in the workshop last night, will sort out that info tonight.

[Pedro]

Very impressive it is too, Jason and many thanks for the Bodmer info. That is a fascinating engine also, but I wouldn't be surprised if it had similar seal problems. The gland on the Xantho is very much longer, which affords greater options. Pat's Audel engine clearly shows a bearing bush, which has to be part of a better solution.
    I've only soldered small assemblies to date, so concerns about getting it right and my experience with "hogging it out" have led me in the barstock direction. I realize now that I was wrong, particularly in this case, with the integral cover, webs and lugs making it impractical, and fabrication has to be the way. (gulp!) This is why I was wondering about lagging, since an all in one Russian iron cover would hide things that individually wooded ones don't.
I've also made myself a victim of "mission creep", obsessing on details and while it's right to examine as many aspects as possible, at some stage sensible decisions must be made.

I have the ME now, and can email the article. There isn't a lot of new info other than one small photo of the finished model, which is a very good job, especially considering the original was only partly deconcreted and still in the tank when the model was finished, though it may well have been updated in the last 20 years.  FYI, Bob Burgess' trunks were 8", crankpins 3/4" and mains 7/8" at 1/6 scale. He also wooded the cylinders, but I'm hoping that was an inaccuracy. Maybe the museum can help.

 It's possible that while they measured everything, they never did proper engineering drawings. just sketches. After all, why  go to the expense as long as the info is clear. I''ll find out soon.

[Pedro]

This is interesting:  http://search.informit.com.au/documentSummary;dn=741576178654316;res=IELENG

It's a preliminary report on recording the engine components with 3d laser scanning with a view to publishing on the net for academics and modellers. Being dated Nov 2013 it looks like it's work in progress, so at a guess will take some time.
I'll find out from the curator when he returns. This paper looks like it is restricted to academics and students so I could only read the precis.