ME 4761 – Sirius Piston Valve C**k up Corner

[Martin ConnellyParticipant @martinconnelly55370]

This one worked for my Sirius.

Martin C

[Charles LamontParticipant @charleslamont71117]

Dave, I did not criticise or point out drawing errors per-se, but rather the whole concept of the article.

By ‘sanity checking’ I meant that Martin should perhaps have thought to himself (as I did when I read it). “Hang on a mo, thousands and thousands of these things have been made over the best part of a century. Is it actually likely there is a design error?”

“Does this even sound right?” is always a good starting point in a world full of total BS.

[Charles LamontParticipant @charleslamont71117]

I have now been sent the relevant parts of the Sirius drawings, sufficient for a complete study of the valve gear.

I can confirm that there is nothing wrong with the original valve drawing as shown and mistakenly complained about in the article.

It does have lots of exhaust clearance, which I had not expected, but which I can see might well be desirable in such a high-speed engine with a small clearance volume. I will do myself a timing diagram sometime out of interest.

One sensible point in the article is that the little sleeve for properly locating the head on the cylinder really ought to be fitted. If the head is only a few thou out of place it significantly messes up the lead.

[Graham MeekParticipant @grahammeek88282]

“As we live in an imperfect world, I advise Model Engineers to assume all plans contain errors.  Never assume that a hobby plan has been sanity checked by someone else.”

Just to put the record straight I have not had any errors reported back to me by those who have built my designs to the drawing. The only time there have been problems is when the builder has decided his method is better and then come back to me to say it did not work.

I have always, always, built the item first, Drawings are amended in the workshop in RED and the computer master updated the same day. The only exception are the designs for the screwcutting clutches which were not built by me, but by friends. Yet none of them had any issues with the drawings.

Back some years ago the Stuart range could be purchased as fully machined kits for a builder to assemble. Clearly the drawings which were supplied for the un-machined kits were exactly the same as those used in the Works, except they all appear on one or two sheets.

From the text of the article through to some comments made on this site. There has been unfounded aspersions made about things in general. To the extent that it may put future constructors off building what is a sound engine.

There are three other points to consider, a slur has been made on the Sirius design, and a slur has been made on all the designs which appear in ME&W, plus this whole episode will do nothing to encourage new writers to the fold.

Regards

Gray,

[duncan webster 1Participant @duncanwebster1]

All this talk of issue 4761, my paper copy hasn’t arrived yet. Anyone else waiting?

[JasonBModerator @jasonb]

Four points if you consider that publishing a misleading and incorrect article will put purchasers off buying and or subscribing.

[Jon Lawes]

On Jon Lawes Said:

On John MC Said:

As an apprentice, late 1970’s, I helped build a Sirius engine.  My employer needed a generating plant that produced no electrical interference, other than that of the generator.    I think the WW2 Alco generator was the inspiration.  We got it machined and running in less than two weeks.  It engine ran most working days for about a year with no attention other than the usual checks.  At some point I think it’s power output was checked, can’t remember the output.  It turned a Lucas motorcycle 120W alternator at, I think, 2500rpm.   All this suggests to me that the drawings are correct, or were correct at the time.

After the work was completed I would see the engine sat on a shelf in the stores until, one day, it wasn’t there…

One thing I cannot remember much about was the steam generator.  It was gas fired and water pumped in manually.

 

I’d love to know what he was using it for!

Unfortunately I don’t remember the purpose of the experiments other than it may have been radio or radar related.

[duncan webster 1]

On duncan webster 1 Said:

All this talk of issue 4761, my paper copy hasn’t arrived yet. Anyone else waiting?

Latest copy dropped through my letterbox about 30 minutes after writing the above, so I can now see what the fuss is about. Mr Quayle has clearly misunderstood how it is meant to work, and his redesign appears to have no steam lap, but it does have exhaust lap. Most unconventional. However, the new scheme does significantly increase the clearance volume, which could have been an advantage if the engine was meant to run at short cutoff, not in this case. The fuss has had one effect, no more locos for me, I don’t have enough years left, but one of these looks like a nice project. Once my new PC arrives I’ll see if I scanned TCs articles and attempt a bar stock version.

[Martin ConnellyParticipant @martinconnelly55370]

The first thought I had when looking at the plans for this valve were that I would need to know where the exhaust ports were in the head and arrange everything to be symmetrical about them. After some thought and looking at other designs I realised that, in theory, this spool valve could be open to atmosphere at both ends and would still work and, as stated, as long as the exhaust ports were open it did not matter where they were positioned. The head is only there to collect and channel away the waste air or steam and do nothing else for the engine apart from making it look neat.

Martin C

[Dave HalfordParticipant @davehalford22513]

And so C**k Up Corner becomes Compost Corner. No doubt a simple sanity check of drawing ‘errors’ would prevent any further buckets of water flying.

 

[duncan webster 1]

On duncan webster 1 Said:

The fuss has had one effect, no more locos for me, I don’t have enough years left, but one of these looks like a nice project. Once my new PC arrives I’ll see if I scanned TCs articles and attempt a bar stock version

Although I generally like to see what is going on I have been thinking of doing one of these enclosed engines for a while and this thread has got me thinking about it a bit more. It was probably going to be based on the MTB 1b or possibly the 1a as the gears are exposed on those and I jave teh 1B drawings. But the Sirius would be another option, maybe a bit smaller like the 3/4″ bore Sun or smaller still if the Sirius was done at 1/16″ = 1mm and I would then have to call it “Twinkle”

[duncan webster 1]

On duncan webster 1 Said:

However, the new scheme does significantly increase the clearance volume, which could have been an advantage if the engine was meant to run at short cutoff, not in this case.

I don’t follow. The smallest clearance volume is normally best for efficiency, whatever the cut-off. However, I think it is the main reason for the large exhaust clearance on the Sirius, in order to avoid excessive compression. (The exhaust is open for about 215° of crank rotation.) I don’t think the concomitant early release would be needed for breathing, rather just an unfortunate consequence of the otherwise elegant (in the Heinz Wolff sense) simplicity of the design.

Out of interest, I have been looking at the timing in more detail. Because this is a single acting engine we don’t have the problem of con-rod angularity making it difficult to equalise events at both ends. It should not be difficult to design for the events for both cylinders to be identical. Even the effects of the angularity of the valve drive buckle can be dealt with pretty easily.

It turns out that, as designed, the events aren’t equal. For example, the flywheel end cylinder (call it F) has 1/64″ lead, and the other one (R) has almost exactly none. Admission, lead, and cutoff can all be made pretty much cock-on simply by shortening the valve length by 0.008″, taking the 2.7″ distance (shown in post #779423 above) to 2.692″, leaving all the other dimensions as drawn.

This alteration also improves the equality of release and compression points, but not quite exactly. These can be equalised by slightly altering the length of the central valve head, but I have not yet worked out by how much.

Equalising the events is a design exercise that may make an engine run more sweetly, but of course it tells us nothing about their suitability. An indicator diagram from one of these engines working at maximum power would be most interesting.

 

 

[John MCParticipant @johnmc39344]

After re-reading this thread my conclusion is that the article in question was one of those solutions to a problem that doesn’t exist.  It would be interesting to hear the authors views on this.

The answer to this and any other problems with published work would be to peer review.   It will not happen, peer reviewing is a long and difficult job to do properly.  Who’s going to do it and how much might it cost?  The lack of peer review is a big failing of the internet as well.

One other point, its been suggested that we should not criticise the article, it might put authors off submitting work for publication.  If one puts their work in to the public domain then criticism, if warranted, should be expected and acted on?

 

 

 

[JasonBModerator @jasonb]

Post Bag has been used for years if someone has a different view or to comment on something that was published. The forum is no different, just a bit faster.

[Graham Meek]

On Graham Meek Said:

“As we live in an imperfect world, I advise Model Engineers to assume all plans contain errors.  Never assume that a hobby plan has been sanity checked by someone else.”

Just to put the record straight I have not had any errors reported back to me by those who have built my designs to the drawing. The only time there have been problems is when the builder has decided his method is …

Graham, I the point I’m making isn’t controversial.  Not a slur for me to discuss an actual real-world problem, of which the Sirius article is one of many examples.

Unfortunately, the reality is that many plans published since the hobby started in the 19th Century have errors.  That’s only to be expected, but unfortunately, there’s no way of recalling them.   Nor is there a system for cataloguing faults.   So if someone reads the ME4761 Sirius article in 2034, he will be misled, unless he finds this topic, or an errata in a later magazine.

If I may, Graham has misunderstood what I’m saying.

• I assert that the set of “all possible hobby plans” contains errors.  This is TRUE.  And by all I mean all, the entirety of hobby plans.
• Graham unilaterally changes my set to “hobby plans published in ME/MEW”, which is different, and uses this to declare a slur.   Graham has moved the goal posts and uses it to criticise me for something I didn’t say. which is unjust!  Nonetheless, this doesn’t change my case because a proportion of what’s published in ME/MEW is erroneous.  A mistake in ME4761 is the subject of this Topic.
• Graham changes the set again!   This time to “hobby plans prepared by Graham Meek”.  That’s miles away from the point I’m making about a massively larger set, and in doing so Graham introduces a serious logic error.  One author doing a good job does not mean everybody else is!

Applying formal logic is an important engineering technique, especially at the design stage.  Engineers have to be careful to solve the right problem.  Avoiding bad decisions due to untested assumptions saves time and money.   I put to readers that Graham’s comments are unhelpful; he turns an engineering issue (faulty plans and what to do about them) into politics (slur accusation, opinion piece, not engineering)   Acid test: does Graham really believe there’s no need for builders to check plans?

Errors aren’t specifically a ME/MEW problem.  They occur in plans published by other magazines, on the web and in  kits.  Fact is hobby plans are of mixed quality and there are no guarantees.  Therefore, I suggest it pays the builder to run his own sanity checks before sinking lots of time and money into making parts.

Simple as that.  No-one needs to follow my advice if they don’t want to.

Dave

PS.   The Sirius mistake is a variant.   By ‘correcting’ a mistake that never existed, seems the author has introduced a new one.   I throw no rocks.  It was done in good faith, and like as not the author had no-one to check it for him.  And it is a truth universally acknowledged that authors can’t see their own mistakes!

[duncan webster 1Participant @duncanwebster1]

Mr Lamont has answered his own question. On an engine with single valve controlling inlet and exhaust, if you run at short cutoff and have a small clearance volume you can get over-compression, where the residual steam is compressed to above boiler pressure. According to the books, GWR locos had ~7% clearance volume, and when running at short cut off would over-compress and discharge via the cylinder relief valves. LMS locos had ~10%and didn’t suffer from this. Clearance volume in this case is a necessary evil. None of this applies to Sirius, which clearly isn’t meant to run at short cutoff.

Something has to compress the residual steam back up to inlet pressure, either the piston or the incoming steam. If it’s the piston this takes energy out of the flywheel, hence tending to make the engine lumpy. How big an effect this is I don’t know. It’s tempting to think that you get this compression energy back as the steam expands, but expansion does not go down to atmospheric pressure before the exhaust opens, so you don’t get it all back.

With an engine with separate inlet and exhaust valves none of this applies and I would expect clearance volumes in big mill engines for instance to be smaller. Perversely, locos with poppet valve cylinders seem to have had larger clearance volumes. I suspect this was a result of the complicated steam passages, but I have no evidence for this.

As Mr Lamont says, an indicator diagram from  a Sirius would be most instructive. The late Prof Hall showed the way, and with more modern things like Arduino and Raspberry Pis it should now be easier. If anyone wants copies of his papers send me a pm, but don’t expect instant answer, my computer is still playing silly, waiting for a replacement

[SillyOldDuffer]

On SillyOldDuffer Said:

On Graham Meek Said:

“As we live in an imperfect world, I advise Model Engineers to assume all plans contain errors.  Never assume that a hobby plan has been sanity checked by someone else.”

Just to put the record straight I have not had any errors reported back to me by those who have built my designs to the drawing. The only time there have been problems is when the builder has decided his method is …

Graham, I the point I’m making isn’t controversial.  Not a slur for me to discuss an actual real-world problem, of which the Sirius article is one of many examples.

Unfortunately, the reality is that many plans published since the hobby started in the 19th Century have errors.  That’s only to be expected, but unfortunately, there’s no way of recalling them.   Nor is there a system for cataloguing faults.   So if someone reads the ME4761 Sirius article in 2034, he will be misled, unless he finds this topic, or an errata in a later magazine.

If I may, Graham has misunderstood what I’m saying.

• I assert that the set of “all possible hobby plans” contains errors.  This is TRUE.  And by all I mean all, the entirety of hobby plans.
• Graham unilaterally changes my set to “hobby plans published in ME/MEW”, which is different, and uses this to declare a slur.   Graham has moved the goal posts and uses it to criticise me for something I didn’t say. which is unjust!  Nonetheless, this doesn’t change my case because a proportion of what’s published in ME/MEW is erroneous.  A mistake in ME4761 is the subject of this Topic.
• Graham changes the set again!   This time to “hobby plans prepared by Graham Meek”.  That’s miles away from the point I’m making about a massively larger set, and in doing so Graham introduces a serious logic error.  One author doing a good job does not mean everybody else is!

Applying formal logic is an important engineering technique, especially at the design stage.  Engineers have to be careful to solve the right problem.  Avoiding bad decisions due to untested assumptions saves time and money.   I put to readers that Graham’s comments are unhelpful; he turns an engineering issue (faulty plans and what to do about them) into politics (slur accusation, opinion piece, not engineering)   Acid test: does Graham really believe there’s no need for builders to check plans?

Errors aren’t specifically a ME/MEW problem.  They occur in plans published by other magazines, on the web and in  kits.  Fact is hobby plans are of mixed quality and there are no guarantees.  Therefore, I suggest it pays the builder to run his own sanity checks before sinking lots of time and money into making parts.

Simple as that.  No-one needs to follow my advice if they don’t want to.

Dave

PS.   The Sirius mistake is a variant.   By ‘correcting’ a mistake that never existed, seems the author has introduced a new one.   I throw no rocks.  It was done in good faith, and like as not the author had no-one to check it for him.  And it is a truth universally acknowledged that authors can’t see their own mistakes!

At the risk of starting World War 3. You make a comment which states “all” plans. If you had said “some” plans I would not have an issue.

When you say “all” that includes my work, which has been proven to be otherwise.

As regards the rest of the above reply. Less is certainly more, as I get word blind by the length of some of the replies given lately.

Regards

Gray,

[noel shelleyParticipant @noelshelley55608]

Having for a while a soft spot for the SIRIUS engine I went up to the library last evening and got out the relevant issues of ME, that run from  V168, 3914 7 Feb 1992 to V170 3938 5 Feb 1993. One point that I had dwelt on was the valve timing,and it’s setting, this article details an eccentric bush in the valve coupling that solves this issue. For anybody wishing to build this engine I say that reading this series will be very helpful not least for the various jigs that aid construction.

As to authors of articles for publication being put off and peer review, the latter is always a wise precaution if possible. Having written a few, I have always tried to read up and check any facts and ask someone who knows hopefully better than me to run through what I have written to spot any obvious errors. I have 2 in the pipeline and I will be surprised if there are not at least differences of opinion, though I hope all errors will have been removed. Put off no, but I could see others being so !

As to what started this, I take it that the author had not seen the Tubal Cain series, as if he had his engine would have run well and had adjustable valve timing.    Ah well. Look forward to 4762 and ME & W. Noel.

[Charles LamontParticipant @charleslamont71117]

Ah, I see. Mr Webster is thinking mainly about variable valve gear, in which case his remarks in post #779651 are quite clear to me. Would not disagree with anything he says above, either. As I have said, the large exhaust clearance of the Sirius is probably necessary to delay the compression point.

First names are OK with me.

[Author]

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