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[Solitary Sailor]

Thanks Bogs

A piece of advise to remember.  Being around this forum is a steep learning curve.

[gondolier88]

Ive got a blowdown valve gauge on order so you can have a look at it when it arrives and see if you like it.

Bigheadedness is never deserved- your engine is definitely something to be proud of!

Greg

[gondolier88]

PS won't give you any more tips on soldering- good to have another professional kinker of pipes onboard!

Greg

[Solitary Sailor]

Hey Greg

Always happy and willing to learn ... none of us know everything, nor anything near. Wasn't it Socrates, when asked what it was like to be so wise and know so much, replied ..."the only thing that I can know of for sure, is how little I know" ...humility never hurt no one ... hubris on the other hand ....

[gondolier88]

I always remember the addages-

'The more you know about something, the more you realise you don't know' and

'Never assume you know a lot about a lot- always remember you know very little about a lot, a lot about very little and you will never know everything'

Greg

[Solitary Sailor]

Well, from this little exchange, I think we can say ... we've both been there and done that 

I've lost count of the times I've made a prat of myself over something unknown ... but I'd far rather a silly question than a stupid mistake any day ... and that applies to which ever end of the question you are on too!

[gondolier88]

Here Here

[Solitary Sailor]

 I should add, I've most definitely had my share of silly mistakes ... which of course, if you are honest with yourself, soon strips you of any delusions of grandeur. Come to think of it, maybe that's what's wrong with our political elites ... they never get to face their own cock-ups  . Now if we can just figure a way to rub their noses in it 

[Solitary Sailor]

Oops! Just remembered, one other part I did not do on the Triple. The valve eccentrics, a very kind neighbor, did one of them completely, and marked out the other two, together with pre drilling the centres. Well, it was a long time ago ... that's my excuse 

Marking out was the hardest part for me, which truth be told I never really mastered all that well ... probably one of the reasons I never tried another project like this one.

[Solitary Sailor]

Just went digging through some old paperwork, and within 2 minutes I found the plans for the Stuart Triple. So here is a shot of part of one page of the plans, showing one of the eccentrics ... now remember, I have no engineering experience, at least in "Tool Making"

Actually, when I first opened up the plans after the kit arrived, I thought "oh my god, what have I done". The whole project could have very easily ended up being started ... followed by much confusion and frustration ... to be discarded as beyond my means. But somehow, for some reason - stubbornness I suppose, I stuck with it, and after much badgering for information and assistance, including one old codger, who kindly lent me the use of his nice big "Boxford" lathe upon which to machine the cylinder castings, (which after completion, he determined I was never going to complete it). The kind neighbor, who was actually often far to busy, but still helpful, and finally that wonderful machinist / shop owner on the Kingston Road, who was a true fount of information, and also, more importantly, full of encouragement for me to continue on, I finally did it. There's a moral there somewhere 

 Don't suppose Stuart Turner will be too upset if I just post one tiny bit of their plans, for illustration purposes.

[Solitary Sailor]

That picture above is of one of the eccentrics. What it doesn't show is that the eccentric for the intermediate cylinder must be split in order to mount it on the crankshaft, just to add to a mind bogglingly complex marking out process, at least to us non machinist / tool maker types. This was the one that my neighbor did for me...thank heavens. 

Talk about stretching your mind   

[gondolier88]

I don't know, and heres me thinking you did everything else!!!! 

I can see that being very difficult- split eccentrics are difficult enough to execute full size!!!

Heres something that you might want to attempt to make!! The slip eccentric reverse mechanism on SY Gondola- 3 concentric shafts- one moving with crankshaft throught the centre of it- with spigots following a helical groove milled into the crankshaft- the other on the outside bolted to the eccentrics acting as the rider for the eccentrics- when the intermediate shaft is pushed in, following the helical groove milled into the crankshaft, it rotates the eccentrics 1/3 turn, reversing the engine- VERY effective- never in 30 years had a problem with it!!

I'll try to find a pic for you!

Greg

[Solitary Sailor]

Mathematics was never going to be the love of my life, I realized that very early on in life, and nothing in the intervening years has done anything to budge that perception ... and yes, yes, I know, without it we'd still be stuck plowing the fields, but that obvious fact doesn't help my poor brain any 

Incidentally, that eccentric shown was one of the ones which slipped over the unobstructed end of the shaft, for the L.P. cylinder valve gear, so it wasn't the split one, which was offset at 15 degrees, at least if memory serves me right ... but there again, that's anybodies guess     

I've sent an email off to Mike at Maccsteam, asking about which boiler would be suitable to power this steam guzzler ... I suspect it's going to be the biggest one ...err, with the exchange rate where it is now, it may be a while before enough pennies roll in ...thanks Mr Politician and Mr Banker    I did try and follow his formula for calculating the required volume of steam output from a given boiler size, but given that this is an expansion engine, I am unsure if this formula holds true ... again, it's the  Maths.

If I recall, the triple was not a particularly fast revving engine, more along the lines of slow, steady and powerful ... it's been so long since I was really into this, I've forgotten most of the details. Whatever, I'm sure the cost of a boiler for this size engine will be more than I can afford right now 

If, however, I do decide to hide that little Puffin in a tug boat, it looks like one of Maccsteams excellent smaller boilers would do the trick, and at a price more to my bank balance's liking 

Finished pulling the little Puffin apart and cleaning her up a bit. The good news is that she went back together very well, and the main springs are still sound, though I think I will take Bogs advice and get a replacement set ... just in case.

Awaiting your piccies Greg.

[gondolier88]

Why not make your own boiler???

You've got all the skills you need.

Greg

[Solitary Sailor]

Wot ... and blow myself up 

Actually, I no longer have the tool set-up with which to prep the boiler before getting the torches out. Nor the space to put it should I go out and get it ... hell, I've run out of space to put the boats I'm building ... though so far that hasn't stopped my production slipways any 

[gondolier88]

  Ok!

Greg

[Solitary Sailor]

Well, little "Puffin" all cleaned up and shiny bright ... almost looks new ... ready for a hull to put her in, oh and maybe a horizontal boiler. Don't worry Greg, I will make the mounting plate so that it is easily removed, and so can be put in an open hull at a later date. Still a long way to go before that, and as my next project is likely to be "Mountfleets" "St Nectan" (with electric power to start with, though a sort of swap out set-up, so that eventually, depending on mood, I can run either/ or ...electric or steam) And no, I don't see this little Puffin pushing St Nectan, most likely a Monahan Heron ... so this little puffin is likely to end up in either an "Envoy or Cruiser Tug... for now ... see, I got grand plans      (on little budget    )

 

[kno3]

Cool Puffin you've got there, it must be one of the nicest oscillators ever built comercially.
I was most impressed with the quality of these little engines when I disassembled mine and stripped the old paint. i was planning to re-paint it, but seeing how perfect the casting was under that old paint, I left the bare metal, it looks so nice.

[AlexC]

Hi Guy's,

Solitary Sailor,

You have made a lovely job of your Stuart Triple, you can be proud of yourself.

A few notes which may be of some help: -

All Cheddar Models boilers use 1/4" x 32tpi ME threads for the water guage connections (boiler bushes).... not 1/4" x 40tpi.


As for the steam requirements of the TRIPLE..... you only need to calculate for the HP cylinder swept volume, since it is the only one actually fed from the boiler. The other cylinders receive steam from the preceding one.

A quick calculation using 600rpm gives approx 530cu in steam / minute required from the boiler.

Multi expansion engines work best with HIGHER pressure into the HP cylinder (usually somewhat superheated) to allow for the larger expansion requirements.

The MAccSteam 4" boiler running at 80psi will give you this with approx 560 cu in steam/minute.... so not as large a boiler as you perhaps anticipated.

Whilst it would be great to see your TRIPLE being used in a model it is not without it's problems.... not the least being: -

Multi expansion engines cannot be guaranteed to self start, and will normally have to be fitted with SIMPLING valves (as per full size) in order to supply steam directly to one, or both, of the lower pressure cylinders.... These would be shut off again immediately after the engine started....... not a problem in a full size vessel, where there is an engine room crew to operate this, but not quite so simple in a model.

It can be done, but it requires a good bit of thinking about in order to accomplish it.

The MaccSteam 3/12" boiler will be more than sufficient for your PUFFIN engine.

Hope this is of some help.

Best regards.

AlexC 



 

[gondolier88]

Hi,

Thanks for correcting me Alex, I thought the gauges were 40tpi.

You are correct in saying that only the swept volume of the HP cylinder needs to be calculated, however the engine would not be working expansively at 80psi- a triple needs at the VERY least 120psi to work as a true triple expansion- 80psi at the boiler would give you roughly 20-25 psi at the valvechest- once this has acted on the HP cylinder the IP will have about 5-15 psi working on it- the LP would then have 0-5psi max- really not working to it's full potential- though it would move it would be very lumpy and would need the cylinder drains open pretty much all the time- unless you could guarentee that you have enough superheat on the supply.

If you wanted to make your own boiler, for less money and with built in safety you could make a low water content watertube boiler, such as a Yarrow, easily run at 150psi- can be made using small bore (read less expense) copper tube, the largest being the header which would need to be roughly 1 1/2 inch- but that would be far less than 5 or 6 inch dia. shell boiler- would also give you less weight should you wish to power a model with it- put a dedicated feed pump on the engine, supply controlled by a water gauge reading bypass valve.

This setup is the safest- even if the worst happened you don't get an explosion- just a whoosh of steam. It's also the cheapest option- no big diameter copper tube- in fact the small bore high pressure tube i'm sure you'd be able to get something suitable through work. They are fast, efficient steam raisers and opperate at much higher pressures than shell boilers purely by their nature- most tests to destruction on Yarrow boilers failed at stupidly high pressures like 2000psi- even then it was the joints that failed not the tubes- thats what I recommend anyway!

Greg

[AlexC]

 

WHAT!!!!!

Sorry Gondolier88....would you care to explain your thinking/reasoning?

If you have the correct dia (bore) of connecting pipework, between the boiler and the HP steam chest, then the pressure at the steam chest will be within 1 PSI or so of that in the boiler (Unless you are using a pressure reducing regulator). The small pressure drop would be due to losses in the pipe work.

In order for the pressure to drop to 20-25psi from 80psi between the boiler and the HP steam chest there would need to be a very large restriction.

The pressure at the IP steam chest would be determined by the CUT-OFF of the HP cylinder valve gear (typically 50% - 90% this being the higher value at starting) so the pressure at the IP steam chest would not drop that much (perhaps down to 50psi from an initial 80psi, assuming the higher cut-off figure of the valve gear).
The same goes for the LP cylinder, which, whilst working at the lowest available input pressure (probably around 20psi at the highest cut-off), would also be working in to a vacuum condenser, and so would be (exhausting) below atmospheric.... as such it is more than capable of doing very useful work.

I think you are getting a bit confused between a YARROW water tube boiler and a MONO tube boiler.

A Yarrow is fitted with a steam drum (the top header) which is a true pressure vessel and it is just a dangerous as any other steam drum type of boiler.... when one of these goes/fails it most certainly will not result in JUST A WHOOSH of steam...... the LATENT energy stored in the top header drum (which would also normally be at least 1/3rd full of water if being fed correctly), and the water in the tubes and bottom headers, would result in the same kind of explosion that any other water drum boiler would produce.

A MONOTUBE (Flash) boiler will only contain a very small amount of water (sufficient only for the immediate steam requirement of the engine) and it does not have a steam reservoir or a water reservoir.... it only produces steam on demand from a controlled water pump system...... these, I will agree, will not normally explode.... but I certainly would not want to be close to one if /when it failed..... SUPERHEATED steam is not funny..... especially at 2000psi.

I certainly agree that a Yarrow type would be a very fast steamer, but it MOST CERTAINLY does not have the built in safety you are suggesting....quite the opposite.
Neither are they operated at much above 500 psi.

Best regards.

AlexC. 

[Solitary Sailor]

Alex, Greg

You guys done yet  ? Now I am confused 

Anyway, hi again Alex, and thanks for the info and the compliment. I have been in touch with Mike at Maccsteam, after telling him about the 'Triple',  he recommends the 5" boiler with the double burner set up, and he agrees with you about the 3 1/2" for the 'Puffin' . He also put me straight about calculating the swept face value of the H.P. cylinder only on an expansion engine. The info about the self starting deficiencies of the 'Triple' are indeed, a little concerning. It seems I would need to look into Simpling valves. If I understand correctly this would be ... simply put ... a momentary injector into one or both of the larger cylinders, somehow timed to open after the H. P. cylinder had reached BDC, or would that be 'mid stroke' as the crankshaft had turned 45 degrees? As I said, I get confused easily 

After having heard of some horror stories of people with too little knowledge, but far too much confidence, where boilers are concerned, I think I'll pass on the homemade front for now ... besides which, there's no one around here who I can go and aggravate the hell out of extracting the much need knowledge and information from   

Greg .. no disrespect, but that's 2 to 1 against ya  . Being such a brave lad, I think I'll defer on the side of caution 

[Solitary Sailor]

Hi kno3

Yes they are nice little engines. I saw your little 'Puffin' getting its bath ... nice and messy 
I agree with some of the commenters on that discussion thread ... I think they look better painted, just something about the contrast between the paint and the bare brass faces and steel bolt heads ... but then again ... beauty is in the eye of the beholder 

[gondolier88]

Alex,

My reasoning is very simple- 'you cannot scale nature' to quote a certain well respected engineer!

In a full size plant you ALWAYS get a drop in pressure from the boiler to the pressure working on the piston- and it is NEVER just 1psi- if only it was!!!!!!

Typically it ranges anything between 20% at best through a typical 40% reduction to 60% in very badly designed pipework.

As for 'using a pressure reducing regulator'- every steam plant in the world has a pressure reducing valve- it's called pipework! This is a huge restriction to saturated steam- which in model plants, even if you have a small superheater, is still saturated- just carrying a bit more heat with it.

Next are all the bends that are incorporated into the pipework- each 90deg. bend will easily knock 3-4psi of the supply- more as the bore of pipes gets smaller- the bore of 3/16" pipe being about 1/6", 3/32" at the most- if you can get 80psi from the boiler through that with typically 3 90deg. bends, plus a main stop-valve at the point of supply, plus an isolation at the engine you'll be rich man mate!!

I have got the formulea somewhere for calculating these losses through resistance should you wish me to prove my reasoning!!

The next thing that impinges on the efficiency of the supply is thermal efficiency- of which i'm sure you'll be well aware practically doesn't exist at model engineering sizes- in a 4" steel pipe with 1 ½” lagging of super efficient heatproof lagging you can knock off 4-5% thermal efficiency. This is through ¼” steel plus 1 ½” mm lagging- giving an overall effective thickness of 1 ¾” from steam to atmosphere.

In a model with 1/16” copper- which dissipates heat quicker than steel- then a max. of 3/32” lagging giving an overall thickness of 5/32” between the steam and atmosphere- at that thickness the lagging serves more to stop us burning ourselves rather than keeping the steam at operating temperature.

As for being confused, I’m well aware of what a monotube boiler is and what the differences are!!!

“A Yarrow is fitted with a steam drum (the top header) which is a true pressure vessel and it is just a dangerous as any other steam drum type of boiler”

No it isn’t, simple as that!!! A typical shell boiler of the same output will contain anything from 150% to 400% more water by volume than a water tube boiler- that is the whole point in having water tubes, not fire tubes!!

Water at steam temperature expands into atmosphere at a ratio of 1600:1- so a model water tube boiler would have typically 300-500ml of water in it- say 400ml average would have a latent potential of;

400 X 1600 = 640000
1000 = 640litres

A typical shell boiler, scotch marine say, of the same output would have on average roughly 1.5-2 litres of water by volume, so the same treatment of this explosion gives;

 1750  X 1600 = 2800000
1000 = 2800 litres

That’s a hell of a lot more damage!!!!

Plus a shell boiler has inherent weaknesses built in- a much larger surface area that can fail- study any instance of boiler explosions and just about all of them are due to negligence, but the cause wasn’t the point of failing- in cases where an engineer would perhaps screw down a safety valve in order to squeeze that bit extra from the boiler, the safety valve would be intact- but it was typically the joint where the outer wrapper of the firebox, the throat plate and the barrel met on loco’ boilers, and on marine and stationary types it would typically be on the seam joint on the outer shell.

Perhaps on reading my post back you will notice I was also not talking about OPERATING these boilers at 2000psi that would be plain stupidity- I said that on TESTS to DESTRUCTION- a very necessary process in the design of any pressure vessel- that they typically failed at 2000psi- some even above that.

However, where they failed was at the joints between the downtubes and the header and mud tubes- but these were never catastrophic- because of the RELATIVE (in comparison) low water content- the water escaping would soon neutralise in pressure due to there not being enough volume behind to rip apart the boiler- only the joint. The other safety feature in this is that the water flashing into steam on escape is taken up through the boiler casing and out through the funnel- not in a massive cloud into atmosphere from the joint.

For operating in model sizes you wouldn’t need to go above 175psi to get the triple to work effectively.

Greg

[AlexC]

 

Hi SS,

Sorry, wasn't trying to start a war or anything, just trying to avoid a potential misconception as regards to safety.

Yes Mike is on the ball with his recommendations, however, I feel he is being just a little over cautious in recommending the 5" boiler.

His 4" boiler is capable (according to his figures) of producing 800 cu ins steam/minute @ 50psi which means the boiler is capable of evaporating just a little under 2 cu ins of water per minute at this pressure.
At 80psi (the max working pressure of the boiler) this same 2 cu ins water will produce 560 cu ins of steam.(Assuming the burner is capable of keeping up with the demand at this pressure)

Since your triple will only require 530 cu in steam/minute @ 600rpm then this should be more than enough for your engine.

Naturally though, should you wish to run faster than this (or the burner was not capable enough) then the larger boiler would be required.

The problem with starting a triple (or any compound engine for that matter) extends from the fact that the engine may STOP with the HP valve gear in such a position that the STEAM ports are CLOSED....... (a few degrees either side of TDC or BDC).... in these instances the engine will not start becouse the steam from the boiler cannot enter the engine and, since the engine was stoped, there would be no (or virtually none) available exhuast steam from the HP cylinder to enter the IP cylinder, or from the IP cylinder into the LP cylinder.

A simple expansion engine (multi cylinders all operating at std boiler pressure) does not suffer from this, since all cylinders are connected directly to the boiler steam feed.

SIMPLING valves are used to turn Compound engines into SIMPLE expansion engines (hence the name), for the purposes of starting them under such conditions and, just as you have said, they are only used to inject steam directly in to the IP and or/LP steam chests in order to drive the crank round to a position where the HP ports/valve is opened... at which point this then takes over and the SIMPLING valve/s can be closed.

On a small model engine, these could simply consist of a servo driven steam valve (operated from a spare channel with which you could momentarily inject steam to get going.... once running you would immediately close them again.

On FULL size ships/vessels... these may or may not include a pressure reducing stage (often included to avoid over pressure damage to the engine) and can be either manually operated (on smaller vessels) or mechanically/hydraulically linked to the normal regulator on larger vessels.

Regardless of the exact mechanism, the engine valve gear would always be placed into full FORWARDS or REVERSE (giving maximum cut-off) before attempting the start.

Once fully under way the valve gear can be backed off (notched up) to reduce the cut-off in order to get the best use of expansion from the steam.

Hope this helps explain things a bit more.

Best regards.

AlexC